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1 | =head1 NAME |
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2 | |
40dbc108 |
3 | DBIx::Class::Manual::Cookbook - Miscellaneous recipes |
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4 | |
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5 | =head1 SEARCHING |
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6 | |
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7 | =head2 Paged results |
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8 | |
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9 | When you expect a large number of results, you can ask L<DBIx::Class> for a |
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10 | paged resultset, which will fetch only a defined number of records at a time: |
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11 | |
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12 | my $rs = $schema->resultset('Artist')->search( |
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13 | undef, |
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14 | { |
15 | page => 1, # page to return (defaults to 1) |
16 | rows => 10, # number of results per page |
17 | }, |
18 | ); |
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19 | |
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20 | return $rs->all(); # all records for page 1 |
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21 | |
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22 | The C<page> attribute does not have to be specified in your search: |
23 | |
24 | my $rs = $schema->resultset('Artist')->search( |
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25 | undef, |
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26 | { |
27 | rows => 10, |
28 | } |
29 | ); |
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30 | |
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31 | return $rs->page(1); # DBIx::Class::ResultSet containing first 10 records |
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32 | |
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33 | In either of the above cases, you can get a L<Data::Page> object for the |
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34 | resultset (suitable for use in e.g. a template) using the C<pager> method: |
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35 | |
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36 | return $rs->pager(); |
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37 | |
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38 | =head2 Complex WHERE clauses |
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39 | |
40dbc108 |
40 | Sometimes you need to formulate a query using specific operators: |
41 | |
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42 | my @albums = $schema->resultset('Album')->search({ |
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43 | artist => { 'like', '%Lamb%' }, |
44 | title => { 'like', '%Fear of Fours%' }, |
45 | }); |
40dbc108 |
46 | |
47 | This results in something like the following C<WHERE> clause: |
48 | |
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49 | WHERE artist LIKE '%Lamb%' AND title LIKE '%Fear of Fours%' |
40dbc108 |
50 | |
51 | Other queries might require slightly more complex logic: |
52 | |
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53 | my @albums = $schema->resultset('Album')->search({ |
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54 | -or => [ |
55 | -and => [ |
56 | artist => { 'like', '%Smashing Pumpkins%' }, |
57 | title => 'Siamese Dream', |
58 | ], |
59 | artist => 'Starchildren', |
60 | ], |
61 | }); |
40dbc108 |
62 | |
63 | This results in the following C<WHERE> clause: |
64 | |
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65 | WHERE ( artist LIKE '%Smashing Pumpkins%' AND title = 'Siamese Dream' ) |
66 | OR artist = 'Starchildren' |
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67 | |
68 | For more information on generating complex queries, see |
69 | L<SQL::Abstract/WHERE CLAUSES>. |
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70 | |
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71 | =head2 Arbitrary SQL through a custom ResultSource |
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72 | |
73 | Sometimes you have to run arbitrary SQL because your query is too complex |
74 | (e.g. it contains Unions, Sub-Selects, Stored Procedures, etc.) or has to |
75 | be optimized for your database in a special way, but you still want to |
76 | get the results as a L<DBIx::Class::ResultSet>. |
77 | The recommended way to accomplish this is by defining a separate ResultSource |
78 | for your query. You can then inject complete SQL statements using a scalar |
79 | reference (this is a feature of L<SQL::Abstract>). |
80 | |
81 | Say you want to run a complex custom query on your user data, here's what |
82 | you have to add to your User class: |
83 | |
84 | package My::Schema::User; |
85 | |
86 | use base qw/DBIx::Class/; |
87 | |
88 | # ->load_components, ->table, ->add_columns, etc. |
89 | |
90 | # Make a new ResultSource based on the User class |
91 | my $source = __PACKAGE__->result_source_instance(); |
92 | my $new_source = $source->new( $source ); |
93 | $new_source->source_name( 'UserFriendsComplex' ); |
94 | |
95 | # Hand in your query as a scalar reference |
96 | # It will be added as a sub-select after FROM, |
97 | # so pay attention to the surrounding brackets! |
98 | $new_source->name( \<<SQL ); |
99 | ( SELECT u.* FROM user u |
100 | INNER JOIN user_friends f ON u.id = f.user_id |
101 | WHERE f.friend_user_id = ? |
102 | UNION |
103 | SELECT u.* FROM user u |
104 | INNER JOIN user_friends f ON u.id = f.friend_user_id |
105 | WHERE f.user_id = ? ) |
106 | SQL |
107 | |
108 | # Finally, register your new ResultSource with your Schema |
109 | My::Schema->register_source( 'UserFriendsComplex' => $new_source ); |
110 | |
111 | Next, you can execute your complex query using bind parameters like this: |
112 | |
113 | my $friends = [ $schema->resultset( 'UserFriendsComplex' )->search( {}, |
114 | { |
115 | bind => [ 12345, 12345 ] |
116 | } |
117 | ) ]; |
118 | |
119 | ... and you'll get back a perfect L<DBIx::Class::ResultSet>. |
120 | |
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121 | =head2 Using specific columns |
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122 | |
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123 | When you only want specific columns from a table, you can use |
124 | C<columns> to specify which ones you need. This is useful to avoid |
125 | loading columns with large amounts of data that you aren't about to |
126 | use anyway: |
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127 | |
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128 | my $rs = $schema->resultset('Artist')->search( |
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129 | undef, |
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130 | { |
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131 | columns => [qw/ name /] |
bade79c4 |
132 | } |
133 | ); |
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134 | |
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135 | # Equivalent SQL: |
136 | # SELECT artist.name FROM artist |
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137 | |
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138 | This is a shortcut for C<select> and C<as>, see below. C<columns> |
139 | cannot be used together with C<select> and C<as>. |
140 | |
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141 | =head2 Using database functions or stored procedures |
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142 | |
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143 | The combination of C<select> and C<as> can be used to return the result of a |
144 | database function or stored procedure as a column value. You use C<select> to |
145 | specify the source for your column value (e.g. a column name, function, or |
146 | stored procedure name). You then use C<as> to set the column name you will use |
147 | to access the returned value: |
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148 | |
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149 | my $rs = $schema->resultset('Artist')->search( |
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150 | {}, |
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151 | { |
152 | select => [ 'name', { LENGTH => 'name' } ], |
153 | as => [qw/ name name_length /], |
154 | } |
155 | ); |
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156 | |
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157 | # Equivalent SQL: |
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158 | # SELECT name name, LENGTH( name ) |
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159 | # FROM artist |
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160 | |
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161 | Note that the C< as > attribute has absolutely nothing to with the sql |
162 | syntax C< SELECT foo AS bar > (see the documentation in |
163 | L<DBIx::Class::ResultSet/ATTRIBUTES>). If your alias exists as a |
164 | column in your base class (i.e. it was added with C<add_columns>), you |
165 | just access it as normal. Our C<Artist> class has a C<name> column, so |
166 | we just use the C<name> accessor: |
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167 | |
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168 | my $artist = $rs->first(); |
169 | my $name = $artist->name(); |
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170 | |
171 | If on the other hand the alias does not correspond to an existing column, you |
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172 | have to fetch the value using the C<get_column> accessor: |
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173 | |
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174 | my $name_length = $artist->get_column('name_length'); |
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175 | |
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176 | If you don't like using C<get_column>, you can always create an accessor for |
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177 | any of your aliases using either of these: |
178 | |
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179 | # Define accessor manually: |
180 | sub name_length { shift->get_column('name_length'); } |
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181 | |
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182 | # Or use DBIx::Class::AccessorGroup: |
183 | __PACKAGE__->mk_group_accessors('column' => 'name_length'); |
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184 | |
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185 | =head2 SELECT DISTINCT with multiple columns |
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186 | |
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187 | my $rs = $schema->resultset('Foo')->search( |
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188 | {}, |
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189 | { |
190 | select => [ |
191 | { distinct => [ $source->columns ] } |
192 | ], |
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193 | as => [ $source->columns ] # remember 'as' is not the same as SQL AS :-) |
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194 | } |
195 | ); |
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196 | |
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197 | my $count = $rs->next->get_column('count'); |
198 | |
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199 | =head2 SELECT COUNT(DISTINCT colname) |
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200 | |
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201 | my $rs = $schema->resultset('Foo')->search( |
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202 | {}, |
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203 | { |
204 | select => [ |
205 | { count => { distinct => 'colname' } } |
206 | ], |
207 | as => [ 'count' ] |
208 | } |
209 | ); |
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210 | |
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211 | =head2 Grouping results |
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212 | |
213 | L<DBIx::Class> supports C<GROUP BY> as follows: |
214 | |
215 | my $rs = $schema->resultset('Artist')->search( |
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216 | {}, |
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217 | { |
218 | join => [qw/ cds /], |
219 | select => [ 'name', { count => 'cds.cdid' } ], |
220 | as => [qw/ name cd_count /], |
221 | group_by => [qw/ name /] |
222 | } |
223 | ); |
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224 | |
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225 | # Equivalent SQL: |
226 | # SELECT name, COUNT( cds.cdid ) FROM artist me |
227 | # LEFT JOIN cd cds ON ( cds.artist = me.artistid ) |
228 | # GROUP BY name |
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229 | |
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230 | Please see L<DBIx::Class::ResultSet/ATTRIBUTES> documentation if you |
231 | are in any way unsure about the use of the attributes above (C< join |
232 | >, C< select >, C< as > and C< group_by >). |
233 | |
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234 | =head2 Predefined searches |
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235 | |
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236 | You can write your own L<DBIx::Class::ResultSet> class by inheriting from it |
74dc2edc |
237 | and define often used searches as methods: |
238 | |
239 | package My::DBIC::ResultSet::CD; |
240 | use strict; |
241 | use warnings; |
242 | use base 'DBIx::Class::ResultSet'; |
243 | |
244 | sub search_cds_ordered { |
245 | my ($self) = @_; |
246 | |
247 | return $self->search( |
248 | {}, |
249 | { order_by => 'name DESC' }, |
250 | ); |
251 | } |
252 | |
253 | 1; |
254 | |
255 | To use your resultset, first tell DBIx::Class to create an instance of it |
256 | for you, in your My::DBIC::Schema::CD class: |
257 | |
258 | __PACKAGE__->resultset_class('My::DBIC::ResultSet::CD'); |
259 | |
260 | Then call your new method in your code: |
261 | |
262 | my $ordered_cds = $schema->resultset('CD')->search_cds_ordered(); |
263 | |
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264 | =head2 Using SQL functions on the left hand side of a comparison |
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265 | |
266 | Using SQL functions on the left hand side of a comparison is generally |
267 | not a good idea since it requires a scan of the entire table. However, |
268 | it can be accomplished with C<DBIx::Class> when necessary. |
269 | |
270 | If you do not have quoting on, simply include the function in your search |
271 | specification as you would any column: |
272 | |
273 | $rs->search({ 'YEAR(date_of_birth)' => 1979 }); |
274 | |
275 | With quoting on, or for a more portable solution, use the C<where> |
276 | attribute: |
277 | |
278 | $rs->search({}, { where => \'YEAR(date_of_birth) = 1979' }); |
279 | |
280 | =begin hidden |
281 | |
282 | (When the bind args ordering bug is fixed, this technique will be better |
283 | and can replace the one above.) |
284 | |
285 | With quoting on, or for a more portable solution, use the C<where> and |
286 | C<bind> attributes: |
287 | |
288 | $rs->search({}, { |
289 | where => \'YEAR(date_of_birth) = ?', |
290 | bind => [ 1979 ] |
291 | }); |
292 | |
293 | =end hidden |
294 | |
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295 | =head1 JOINS AND PREFETCHING |
296 | |
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297 | =head2 Using joins and prefetch |
298 | |
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299 | You can use the C<join> attribute to allow searching on, or sorting your |
300 | results by, one or more columns in a related table. To return all CDs matching |
301 | a particular artist name: |
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302 | |
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303 | my $rs = $schema->resultset('CD')->search( |
304 | { |
305 | 'artist.name' => 'Bob Marley' |
306 | }, |
307 | { |
308 | join => [qw/artist/], # join the artist table |
309 | } |
310 | ); |
311 | |
312 | # Equivalent SQL: |
313 | # SELECT cd.* FROM cd |
314 | # JOIN artist ON cd.artist = artist.id |
315 | # WHERE artist.name = 'Bob Marley' |
316 | |
317 | If required, you can now sort on any column in the related tables by including |
318 | it in your C<order_by> attribute: |
319 | |
320 | my $rs = $schema->resultset('CD')->search( |
321 | { |
322 | 'artist.name' => 'Bob Marley' |
323 | }, |
324 | { |
325 | join => [qw/ artist /], |
326 | order_by => [qw/ artist.name /] |
327 | } |
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328 | ); |
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329 | |
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330 | # Equivalent SQL: |
331 | # SELECT cd.* FROM cd |
332 | # JOIN artist ON cd.artist = artist.id |
333 | # WHERE artist.name = 'Bob Marley' |
334 | # ORDER BY artist.name |
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335 | |
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336 | Note that the C<join> attribute should only be used when you need to search or |
337 | sort using columns in a related table. Joining related tables when you only |
338 | need columns from the main table will make performance worse! |
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339 | |
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340 | Now let's say you want to display a list of CDs, each with the name of the |
341 | artist. The following will work fine: |
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342 | |
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343 | while (my $cd = $rs->next) { |
344 | print "CD: " . $cd->title . ", Artist: " . $cd->artist->name; |
345 | } |
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346 | |
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347 | There is a problem however. We have searched both the C<cd> and C<artist> tables |
348 | in our main query, but we have only returned data from the C<cd> table. To get |
349 | the artist name for any of the CD objects returned, L<DBIx::Class> will go back |
350 | to the database: |
ea6309e2 |
351 | |
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352 | SELECT artist.* FROM artist WHERE artist.id = ? |
ea6309e2 |
353 | |
354 | A statement like the one above will run for each and every CD returned by our |
355 | main query. Five CDs, five extra queries. A hundred CDs, one hundred extra |
356 | queries! |
357 | |
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358 | Thankfully, L<DBIx::Class> has a C<prefetch> attribute to solve this problem. |
897342e4 |
359 | This allows you to fetch results from related tables in advance: |
ea6309e2 |
360 | |
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361 | my $rs = $schema->resultset('CD')->search( |
362 | { |
363 | 'artist.name' => 'Bob Marley' |
364 | }, |
365 | { |
366 | join => [qw/ artist /], |
367 | order_by => [qw/ artist.name /], |
368 | prefetch => [qw/ artist /] # return artist data too! |
369 | } |
370 | ); |
ea6309e2 |
371 | |
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372 | # Equivalent SQL (note SELECT from both "cd" and "artist"): |
373 | # SELECT cd.*, artist.* FROM cd |
374 | # JOIN artist ON cd.artist = artist.id |
375 | # WHERE artist.name = 'Bob Marley' |
376 | # ORDER BY artist.name |
ea6309e2 |
377 | |
378 | The code to print the CD list remains the same: |
379 | |
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380 | while (my $cd = $rs->next) { |
381 | print "CD: " . $cd->title . ", Artist: " . $cd->artist->name; |
382 | } |
ea6309e2 |
383 | |
bade79c4 |
384 | L<DBIx::Class> has now prefetched all matching data from the C<artist> table, |
ea6309e2 |
385 | so no additional SQL statements are executed. You now have a much more |
386 | efficient query. |
387 | |
77d6b403 |
388 | Note that as of L<DBIx::Class> 0.05999_01, C<prefetch> I<can> be used with |
389 | C<has_many> relationships. |
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390 | |
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391 | Also note that C<prefetch> should only be used when you know you will |
ea6309e2 |
392 | definitely use data from a related table. Pre-fetching related tables when you |
393 | only need columns from the main table will make performance worse! |
394 | |
d2f3e87b |
395 | =head2 Multi-step joins |
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396 | |
397 | Sometimes you want to join more than one relationship deep. In this example, |
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398 | we want to find all C<Artist> objects who have C<CD>s whose C<LinerNotes> |
399 | contain a specific string: |
400 | |
401 | # Relationships defined elsewhere: |
402 | # Artist->has_many('cds' => 'CD', 'artist'); |
403 | # CD->has_one('liner_notes' => 'LinerNotes', 'cd'); |
404 | |
405 | my $rs = $schema->resultset('Artist')->search( |
406 | { |
407 | 'liner_notes.notes' => { 'like', '%some text%' }, |
408 | }, |
409 | { |
410 | join => { |
411 | 'cds' => 'liner_notes' |
412 | } |
413 | } |
414 | ); |
ea6309e2 |
415 | |
bade79c4 |
416 | # Equivalent SQL: |
417 | # SELECT artist.* FROM artist |
418 | # JOIN ( cd ON artist.id = cd.artist ) |
419 | # JOIN ( liner_notes ON cd.id = liner_notes.cd ) |
420 | # WHERE liner_notes.notes LIKE '%some text%' |
ea6309e2 |
421 | |
422 | Joins can be nested to an arbitrary level. So if we decide later that we |
423 | want to reduce the number of Artists returned based on who wrote the liner |
424 | notes: |
425 | |
bade79c4 |
426 | # Relationship defined elsewhere: |
427 | # LinerNotes->belongs_to('author' => 'Person'); |
428 | |
429 | my $rs = $schema->resultset('Artist')->search( |
430 | { |
431 | 'liner_notes.notes' => { 'like', '%some text%' }, |
432 | 'author.name' => 'A. Writer' |
433 | }, |
434 | { |
435 | join => { |
436 | 'cds' => { |
437 | 'liner_notes' => 'author' |
ea6309e2 |
438 | } |
bade79c4 |
439 | } |
440 | } |
441 | ); |
ea6309e2 |
442 | |
bade79c4 |
443 | # Equivalent SQL: |
444 | # SELECT artist.* FROM artist |
445 | # JOIN ( cd ON artist.id = cd.artist ) |
446 | # JOIN ( liner_notes ON cd.id = liner_notes.cd ) |
447 | # JOIN ( author ON author.id = liner_notes.author ) |
448 | # WHERE liner_notes.notes LIKE '%some text%' |
449 | # AND author.name = 'A. Writer' |
87980de7 |
450 | |
897342e4 |
451 | =head2 Multi-step prefetch |
452 | |
453 | From 0.04999_05 onwards, C<prefetch> can be nested more than one relationship |
454 | deep using the same syntax as a multi-step join: |
455 | |
456 | my $rs = $schema->resultset('Tag')->search( |
ac2803ef |
457 | {}, |
897342e4 |
458 | { |
459 | prefetch => { |
460 | cd => 'artist' |
461 | } |
462 | } |
463 | ); |
464 | |
465 | # Equivalent SQL: |
466 | # SELECT tag.*, cd.*, artist.* FROM tag |
467 | # JOIN cd ON tag.cd = cd.cdid |
468 | # JOIN artist ON cd.artist = artist.artistid |
469 | |
470 | Now accessing our C<cd> and C<artist> relationships does not need additional |
471 | SQL statements: |
472 | |
473 | my $tag = $rs->first; |
474 | print $tag->cd->artist->name; |
475 | |
d2f3e87b |
476 | =head1 ROW-LEVEL OPERATIONS |
477 | |
478 | =head2 Retrieving a row object's Schema |
479 | |
480 | It is possible to get a Schema object from a row object like so: |
481 | |
482 | my $schema = $cd->result_source->schema; |
483 | # use the schema as normal: |
484 | my $artist_rs = $schema->resultset('Artist'); |
485 | |
486 | This can be useful when you don't want to pass around a Schema object to every |
487 | method. |
488 | |
489 | =head2 Getting the value of the primary key for the last database insert |
490 | |
491 | AKA getting last_insert_id |
492 | |
493 | If you are using PK::Auto (which is a core component as of 0.07), this is |
494 | straightforward: |
495 | |
496 | my $foo = $rs->create(\%blah); |
497 | # do more stuff |
498 | my $id = $foo->id; # foo->my_primary_key_field will also work. |
499 | |
500 | If you are not using autoincrementing primary keys, this will probably |
501 | not work, but then you already know the value of the last primary key anyway. |
502 | |
503 | =head2 Stringification |
504 | |
505 | Employ the standard stringification technique by using the C<overload> |
506 | module. |
507 | |
508 | To make an object stringify itself as a single column, use something |
509 | like this (replace C<foo> with the column/method of your choice): |
510 | |
511 | use overload '""' => sub { shift->name}, fallback => 1; |
512 | |
513 | For more complex stringification, you can use an anonymous subroutine: |
514 | |
515 | use overload '""' => sub { $_[0]->name . ", " . |
516 | $_[0]->address }, fallback => 1; |
517 | |
518 | =head3 Stringification Example |
519 | |
520 | Suppose we have two tables: C<Product> and C<Category>. The table |
521 | specifications are: |
522 | |
523 | Product(id, Description, category) |
524 | Category(id, Description) |
525 | |
526 | C<category> is a foreign key into the Category table. |
527 | |
528 | If you have a Product object C<$obj> and write something like |
529 | |
530 | print $obj->category |
531 | |
532 | things will not work as expected. |
533 | |
534 | To obtain, for example, the category description, you should add this |
535 | method to the class defining the Category table: |
536 | |
537 | use overload "" => sub { |
538 | my $self = shift; |
539 | |
540 | return $self->Description; |
541 | }, fallback => 1; |
542 | |
543 | =head2 Want to know if find_or_create found or created a row? |
544 | |
545 | Just use C<find_or_new> instead, then check C<in_storage>: |
546 | |
547 | my $obj = $rs->find_or_new({ blah => 'blarg' }); |
548 | unless ($obj->in_storage) { |
549 | $obj->insert; |
550 | # do whatever else you wanted if it was a new row |
551 | } |
552 | |
553 | =head2 Dynamic Sub-classing DBIx::Class proxy classes |
554 | |
555 | AKA multi-class object inflation from one table |
556 | |
557 | L<DBIx::Class> classes are proxy classes, therefore some different |
558 | techniques need to be employed for more than basic subclassing. In |
559 | this example we have a single user table that carries a boolean bit |
560 | for admin. We would like like to give the admin users |
561 | objects(L<DBIx::Class::Row>) the same methods as a regular user but |
562 | also special admin only methods. It doesn't make sense to create two |
563 | seperate proxy-class files for this. We would be copying all the user |
564 | methods into the Admin class. There is a cleaner way to accomplish |
565 | this. |
566 | |
567 | Overriding the C<inflate_result> method within the User proxy-class |
568 | gives us the effect we want. This method is called by |
569 | L<DBIx::Class::ResultSet> when inflating a result from storage. So we |
570 | grab the object being returned, inspect the values we are looking for, |
571 | bless it if it's an admin object, and then return it. See the example |
572 | below: |
573 | |
574 | B<Schema Definition> |
575 | |
576 | package DB::Schema; |
577 | |
578 | use base qw/DBIx::Class::Schema/; |
579 | |
580 | __PACKAGE__->load_classes(qw/User/); |
581 | |
582 | |
583 | B<Proxy-Class definitions> |
584 | |
585 | package DB::Schema::User; |
586 | |
587 | use strict; |
588 | use warnings; |
589 | use base qw/DBIx::Class/; |
590 | |
591 | ### Defined what our admin class is for ensure_class_loaded |
592 | my $admin_class = __PACKAGE__ . '::Admin'; |
593 | |
594 | __PACKAGE__->load_components(qw/Core/); |
595 | |
596 | __PACKAGE__->table('users'); |
597 | |
598 | __PACKAGE__->add_columns(qw/user_id email password |
599 | firstname lastname active |
600 | admin/); |
601 | |
602 | __PACKAGE__->set_primary_key('user_id'); |
603 | |
604 | sub inflate_result { |
605 | my $self = shift; |
606 | my $ret = $self->next::method(@_); |
607 | if( $ret->admin ) {### If this is an admin rebless for extra functions |
608 | $self->ensure_class_loaded( $admin_class ); |
609 | bless $ret, $admin_class; |
610 | } |
611 | return $ret; |
612 | } |
613 | |
614 | sub hello { |
615 | print "I am a regular user.\n"; |
616 | return ; |
617 | } |
618 | |
619 | |
620 | package DB::Schema::User::Admin; |
621 | |
622 | use strict; |
623 | use warnings; |
624 | use base qw/DB::Schema::User/; |
625 | |
626 | sub hello |
627 | { |
628 | print "I am an admin.\n"; |
629 | return; |
630 | } |
631 | |
632 | sub do_admin_stuff |
633 | { |
634 | print "I am doing admin stuff\n"; |
635 | return ; |
636 | } |
637 | |
638 | B<Test File> test.pl |
639 | |
640 | use warnings; |
641 | use strict; |
642 | use DB::Schema; |
643 | |
644 | my $user_data = { email => 'someguy@place.com', |
645 | password => 'pass1', |
646 | admin => 0 }; |
647 | |
648 | my $admin_data = { email => 'someadmin@adminplace.com', |
649 | password => 'pass2', |
650 | admin => 1 }; |
651 | |
652 | my $schema = DB::Schema->connection('dbi:Pg:dbname=test'); |
653 | |
654 | $schema->resultset('User')->create( $user_data ); |
655 | $schema->resultset('User')->create( $admin_data ); |
656 | |
657 | ### Now we search for them |
658 | my $user = $schema->resultset('User')->single( $user_data ); |
659 | my $admin = $schema->resultset('User')->single( $admin_data ); |
660 | |
661 | print ref $user, "\n"; |
662 | print ref $admin, "\n"; |
663 | |
664 | print $user->password , "\n"; # pass1 |
665 | print $admin->password , "\n";# pass2; inherited from User |
666 | print $user->hello , "\n";# I am a regular user. |
667 | print $admin->hello, "\n";# I am an admin. |
668 | |
669 | ### The statement below will NOT print |
670 | print "I can do admin stuff\n" if $user->can('do_admin_stuff'); |
671 | ### The statement below will print |
672 | print "I can do admin stuff\n" if $admin->can('do_admin_stuff'); |
673 | |
674 | =head2 Skip object creation for faster results |
675 | |
676 | DBIx::Class is not built for speed, it's built for convenience and |
677 | ease of use, but sometimes you just need to get the data, and skip the |
678 | fancy objects. |
679 | |
680 | To do this simply use L<DBIx::Class::ResultClass::HashRefInflator>. |
681 | |
682 | my $rs = $schema->resultset('CD'); |
683 | |
684 | $rs->result_class('DBIx::Class::ResultClass::HashRefInflator'); |
685 | |
686 | my $hash_ref = $rs->find(1); |
687 | |
688 | Wasn't that easy? |
689 | |
690 | =head2 Get raw data for blindingly fast results |
691 | |
692 | If the L<HashRefInflator|DBIx::Class::ResultClass::HashRefInflator> solution |
693 | above is not fast enough for you, you can use a DBIx::Class to return values |
694 | exactly as they come out of the data base with none of the convenience methods |
695 | wrapped round them. |
696 | |
697 | This is used like so:- |
698 | |
699 | my $cursor = $rs->cursor |
700 | while (my @vals = $cursor->next) { |
701 | # use $val[0..n] here |
702 | } |
703 | |
704 | You will need to map the array offsets to particular columns (you can |
705 | use the I<select> attribute of C<search()> to force ordering). |
706 | |
707 | =head1 RESULTSET OPERATIONS |
708 | |
709 | =head2 Getting Schema from a ResultSet |
710 | |
711 | To get the schema object from a result set, do the following: |
712 | |
713 | $rs->result_source->schema |
714 | |
715 | =head2 Getting Columns Of Data |
716 | |
717 | AKA Aggregating Data |
ac2803ef |
718 | |
719 | If you want to find the sum of a particular column there are several |
720 | ways, the obvious one is to use search: |
721 | |
722 | my $rs = $schema->resultset('Items')->search( |
723 | {}, |
724 | { |
725 | select => [ { sum => 'Cost' } ], |
d676881f |
726 | as => [ 'total_cost' ], # remember this 'as' is for DBIx::Class::ResultSet not SQL |
ac2803ef |
727 | } |
728 | ); |
729 | my $tc = $rs->first->get_column('total_cost'); |
730 | |
731 | Or, you can use the L<DBIx::Class::ResultSetColumn>, which gets |
732 | returned when you ask the C<ResultSet> for a column using |
733 | C<get_column>: |
734 | |
735 | my $cost = $schema->resultset('Items')->get_column('Cost'); |
736 | my $tc = $cost->sum; |
737 | |
738 | With this you can also do: |
739 | |
740 | my $minvalue = $cost->min; |
741 | my $maxvalue = $cost->max; |
742 | |
743 | Or just iterate through the values of this column only: |
744 | |
745 | while ( my $c = $cost->next ) { |
746 | print $c; |
747 | } |
748 | |
749 | foreach my $c ($cost->all) { |
750 | print $c; |
751 | } |
752 | |
709353af |
753 | C<ResultSetColumn> only has a limited number of built-in functions, if |
754 | you need one that it doesn't have, then you can use the C<func> method |
755 | instead: |
756 | |
757 | my $avg = $cost->func('AVERAGE'); |
758 | |
759 | This will cause the following SQL statement to be run: |
760 | |
761 | SELECT AVERAGE(Cost) FROM Items me |
762 | |
763 | Which will of course only work if your database supports this function. |
ac2803ef |
764 | See L<DBIx::Class::ResultSetColumn> for more documentation. |
765 | |
d2f3e87b |
766 | =head1 USING RELATIONSHIPS |
acee4e4d |
767 | |
d2f3e87b |
768 | =head2 Create a new row in a related table |
acee4e4d |
769 | |
6f1434fd |
770 | my $author = $book->create_related('author', { name => 'Fred'}); |
acee4e4d |
771 | |
d2f3e87b |
772 | =head2 Search in a related table |
acee4e4d |
773 | |
774 | Only searches for books named 'Titanic' by the author in $author. |
775 | |
6f1434fd |
776 | my $books_rs = $author->search_related('books', { name => 'Titanic' }); |
acee4e4d |
777 | |
d2f3e87b |
778 | =head2 Delete data in a related table |
acee4e4d |
779 | |
780 | Deletes only the book named Titanic by the author in $author. |
781 | |
6f1434fd |
782 | $author->delete_related('books', { name => 'Titanic' }); |
acee4e4d |
783 | |
d2f3e87b |
784 | =head2 Ordering a relationship result set |
f8bad769 |
785 | |
786 | If you always want a relation to be ordered, you can specify this when you |
787 | create the relationship. |
788 | |
6f1434fd |
789 | To order C<< $book->pages >> by descending page_number, create the relation |
790 | as follows: |
f8bad769 |
791 | |
6f1434fd |
792 | __PACKAGE__->has_many('pages' => 'Page', 'book', { order_by => \'page_number DESC'} ); |
f8bad769 |
793 | |
d2f3e87b |
794 | =head2 Many-to-many relationships |
f8bad769 |
795 | |
d2f3e87b |
796 | This is straightforward using L<ManyToMany|DBIx::Class::Relationship/many_to_many>: |
f8bad769 |
797 | |
d2f3e87b |
798 | package My::User; |
6f1434fd |
799 | use base 'DBIx::Class'; |
800 | __PACKAGE__->load_components('Core'); |
d2f3e87b |
801 | __PACKAGE__->table('user'); |
802 | __PACKAGE__->add_columns(qw/id name/); |
803 | __PACKAGE__->set_primary_key('id'); |
804 | __PACKAGE__->has_many('user_address' => 'My::UserAddress', 'user'); |
805 | __PACKAGE__->many_to_many('addresses' => 'user_address', 'address'); |
87980de7 |
806 | |
d2f3e87b |
807 | package My::UserAddress; |
6f1434fd |
808 | use base 'DBIx::Class'; |
809 | __PACKAGE__->load_components('Core'); |
d2f3e87b |
810 | __PACKAGE__->table('user_address'); |
811 | __PACKAGE__->add_columns(qw/user address/); |
812 | __PACKAGE__->set_primary_key(qw/user address/); |
813 | __PACKAGE__->belongs_to('user' => 'My::User'); |
814 | __PACKAGE__->belongs_to('address' => 'My::Address'); |
181a28f4 |
815 | |
d2f3e87b |
816 | package My::Address; |
6f1434fd |
817 | use base 'DBIx::Class'; |
818 | __PACKAGE__->load_components('Core'); |
d2f3e87b |
819 | __PACKAGE__->table('address'); |
820 | __PACKAGE__->add_columns(qw/id street town area_code country/); |
821 | __PACKAGE__->set_primary_key('id'); |
822 | __PACKAGE__->has_many('user_address' => 'My::UserAddress', 'address'); |
823 | __PACKAGE__->many_to_many('users' => 'user_address', 'user'); |
824 | |
825 | $rs = $user->addresses(); # get all addresses for a user |
826 | $rs = $address->users(); # get all users for an address |
827 | |
828 | =head1 TRANSACTIONS |
829 | |
830 | As of version 0.04001, there is improved transaction support in |
831 | L<DBIx::Class::Storage> and L<DBIx::Class::Schema>. Here is an |
832 | example of the recommended way to use it: |
833 | |
834 | my $genus = $schema->resultset('Genus')->find(12); |
835 | |
836 | my $coderef2 = sub { |
837 | $genus->extinct(1); |
838 | $genus->update; |
839 | }; |
70634260 |
840 | |
181a28f4 |
841 | my $coderef1 = sub { |
35d4fe78 |
842 | $genus->add_to_species({ name => 'troglodyte' }); |
843 | $genus->wings(2); |
844 | $genus->update; |
6f1434fd |
845 | $schema->txn_do($coderef2); # Can have a nested transaction. Only the outer will actualy commit |
181a28f4 |
846 | return $genus->species; |
847 | }; |
848 | |
181a28f4 |
849 | my $rs; |
850 | eval { |
70634260 |
851 | $rs = $schema->txn_do($coderef1); |
181a28f4 |
852 | }; |
853 | |
854 | if ($@) { # Transaction failed |
855 | die "the sky is falling!" # |
856 | if ($@ =~ /Rollback failed/); # Rollback failed |
857 | |
858 | deal_with_failed_transaction(); |
35d4fe78 |
859 | } |
87980de7 |
860 | |
181a28f4 |
861 | Nested transactions will work as expected. That is, only the outermost |
862 | transaction will actually issue a commit to the $dbh, and a rollback |
863 | at any level of any transaction will cause the entire nested |
864 | transaction to fail. Support for savepoints and for true nested |
40dbc108 |
865 | transactions (for databases that support them) will hopefully be added |
866 | in the future. |
ee38fa40 |
867 | |
d2f3e87b |
868 | =head1 SQL |
ee38fa40 |
869 | |
d2f3e87b |
870 | =head2 Creating Schemas From An Existing Database |
ea6309e2 |
871 | |
d2f3e87b |
872 | L<DBIx::Class::Schema::Loader> will connect to a database and create a |
873 | L<DBIx::Class::Schema> and associated sources by examining the database. |
bade79c4 |
874 | |
d2f3e87b |
875 | The recommend way of achieving this is to use the |
876 | L<make_schema_at|DBIx::Class::Schema::Loader/make_schema_at> method: |
bade79c4 |
877 | |
6f1434fd |
878 | perl -MDBIx::Class::Schema::Loader=make_schema_at,dump_to_dir:./lib \ |
879 | -e 'make_schema_at("My::Schema", { debug => 1 }, [ "dbi:Pg:dbname=foo","postgres" ])' |
362500af |
880 | |
d2f3e87b |
881 | This will create a tree of files rooted at C<./lib/My/Schema/> containing |
882 | source definitions for all the tables found in the C<foo> database. |
362500af |
883 | |
d2f3e87b |
884 | =head2 Creating DDL SQL |
362500af |
885 | |
264f1571 |
886 | The following functionality requires you to have L<SQL::Translator> |
887 | (also known as "SQL Fairy") installed. |
362500af |
888 | |
264f1571 |
889 | To create a set of database-specific .sql files for the above schema: |
362500af |
890 | |
264f1571 |
891 | my $schema = My::Schema->connect($dsn); |
892 | $schema->create_ddl_dir(['MySQL', 'SQLite', 'PostgreSQL'], |
893 | '0.1', |
d2f3e87b |
894 | './dbscriptdir/' |
264f1571 |
895 | ); |
896 | |
897 | By default this will create schema files in the current directory, for |
898 | MySQL, SQLite and PostgreSQL, using the $VERSION from your Schema.pm. |
899 | |
900 | To create a new database using the schema: |
901 | |
902 | my $schema = My::Schema->connect($dsn); |
903 | $schema->deploy({ add_drop_tables => 1}); |
904 | |
905 | To import created .sql files using the mysql client: |
906 | |
907 | mysql -h "host" -D "database" -u "user" -p < My_Schema_1.0_MySQL.sql |
908 | |
909 | To create C<ALTER TABLE> conversion scripts to update a database to a |
910 | newer version of your schema at a later point, first set a new |
d2f3e87b |
911 | C<$VERSION> in your Schema file, then: |
264f1571 |
912 | |
913 | my $schema = My::Schema->connect($dsn); |
914 | $schema->create_ddl_dir(['MySQL', 'SQLite', 'PostgreSQL'], |
915 | '0.2', |
916 | '/dbscriptdir/', |
917 | '0.1' |
918 | ); |
919 | |
920 | This will produce new database-specific .sql files for the new version |
921 | of the schema, plus scripts to convert from version 0.1 to 0.2. This |
922 | requires that the files for 0.1 as created above are available in the |
923 | given directory to diff against. |
362500af |
924 | |
6f1434fd |
925 | =head2 Select from dual |
16cd5b28 |
926 | |
927 | Dummy tables are needed by some databases to allow calling functions |
928 | or expressions that aren't based on table content, for examples of how |
929 | this applies to various database types, see: |
930 | L<http://troels.arvin.dk/db/rdbms/#other-dummy_table>. |
931 | |
932 | Note: If you're using Oracles dual table don't B<ever> do anything |
933 | other than a select, if you CRUD on your dual table you *will* break |
934 | your database. |
935 | |
936 | Make a table class as you would for any other table |
937 | |
938 | package MyAppDB::Dual; |
939 | use strict; |
940 | use warnings; |
941 | use base 'DBIx::Class'; |
942 | __PACKAGE__->load_components("Core"); |
943 | __PACKAGE__->table("Dual"); |
944 | __PACKAGE__->add_columns( |
945 | "dummy", |
946 | { data_type => "VARCHAR2", is_nullable => 0, size => 1 }, |
947 | ); |
948 | |
949 | Once you've loaded your table class select from it using C<select> |
950 | and C<as> instead of C<columns> |
951 | |
952 | my $rs = $schema->resultset('Dual')->search(undef, |
953 | { select => [ 'sydate' ], |
954 | as => [ 'now' ] |
955 | }, |
956 | ); |
957 | |
958 | All you have to do now is be careful how you access your resultset, the below |
959 | will not work because there is no column called 'now' in the Dual table class |
960 | |
961 | while (my $dual = $rs->next) { |
962 | print $dual->now."\n"; |
963 | } |
6f1434fd |
964 | # Can't locate object method "now" via package "MyAppDB::Dual" at headshot.pl line 23. |
16cd5b28 |
965 | |
966 | You could of course use 'dummy' in C<as> instead of 'now', or C<add_columns> to |
967 | your Dual class for whatever you wanted to select from dual, but that's just |
968 | silly, instead use C<get_column> |
969 | |
970 | while (my $dual = $rs->next) { |
971 | print $dual->get_column('now')."\n"; |
972 | } |
973 | |
974 | Or use C<cursor> |
975 | |
976 | my $cursor = $rs->cursor; |
977 | while (my @vals = $cursor->next) { |
978 | print $vals[0]."\n"; |
979 | } |
980 | |
981 | Or use L<DBIx::Class::ResultClass::HashRefInflator> |
982 | |
983 | $rs->result_class('DBIx::Class::ResultClass::HashRefInflator'); |
984 | while ( my $dual = $rs->next ) { |
985 | print $dual->{now}."\n"; |
986 | } |
987 | |
988 | Here are some example C<select> conditions to illustrate the different syntax |
989 | you could use for doing stuff like |
990 | C<oracles.heavily(nested(functions_can('take', 'lots'), OF), 'args')> |
991 | |
992 | # get a sequence value |
993 | select => [ 'A_SEQ.nextval' ], |
994 | |
995 | # get create table sql |
996 | select => [ { 'dbms_metadata.get_ddl' => [ "'TABLE'", "'ARTIST'" ]} ], |
997 | |
998 | # get a random num between 0 and 100 |
999 | select => [ { "trunc" => [ { "dbms_random.value" => [0,100] } ]} ], |
1000 | |
1001 | # what year is it? |
1002 | select => [ { 'extract' => [ \'year from sysdate' ] } ], |
1003 | |
1004 | # do some math |
1005 | select => [ {'round' => [{'cos' => [ \'180 * 3.14159265359/180' ]}]}], |
1006 | |
1007 | # which day of the week were you born on? |
6f1434fd |
1008 | select => [{'to_char' => [{'to_date' => [ "'25-DEC-1980'", "'dd-mon-yyyy'" ]}, "'day'"]}], |
16cd5b28 |
1009 | |
1010 | # select 16 rows from dual |
1011 | select => [ "'hello'" ], |
1012 | as => [ 'world' ], |
1013 | group_by => [ 'cube( 1, 2, 3, 4 )' ], |
1014 | |
1015 | |
1016 | |
d2f3e87b |
1017 | =head2 Adding Indexes And Functions To Your SQL |
362500af |
1018 | |
d2f3e87b |
1019 | Often you will want indexes on columns on your table to speed up searching. To |
1020 | do this, create a method called C<sqlt_deploy_hook> in the relevant source |
1021 | class: |
b0a20454 |
1022 | |
d2f3e87b |
1023 | package My::Schema::Artist; |
b0a20454 |
1024 | |
d2f3e87b |
1025 | __PACKAGE__->table('artist'); |
1026 | __PACKAGE__->add_columns(id => { ... }, name => { ... }) |
b0a20454 |
1027 | |
d2f3e87b |
1028 | sub sqlt_deploy_hook { |
1029 | my ($self, $sqlt_table) = @_; |
1030 | |
1031 | $sqlt_table->add_index(name => 'idx_name', fields => ['name']); |
1032 | } |
1033 | |
1034 | 1; |
1035 | |
1036 | Sometimes you might want to change the index depending on the type of the |
1037 | database for which SQL is being generated: |
1038 | |
1039 | my ($db_type = $sqlt_table->schema->translator->producer_type) |
1040 | =~ s/^SQL::Translator::Producer:://; |
1041 | |
1042 | You can also add hooks to the schema level to stop certain tables being |
1043 | created: |
1044 | |
1045 | package My::Schema; |
1046 | |
1047 | ... |
1048 | |
1049 | sub sqlt_deploy_hook { |
1050 | my ($self, $sqlt_schema) = @_; |
1051 | |
1052 | $sqlt_schema->drop_table('table_name'); |
1053 | } |
1054 | |
1055 | You could also add views or procedures to the output using |
1056 | L<SQL::Translator::Schema/add_view> or |
1057 | L<SQL::Translator::Schema/add_procedure>. |
b0a20454 |
1058 | |
362500af |
1059 | =head2 Schema versioning |
1060 | |
1061 | The following example shows simplistically how you might use DBIx::Class to |
1062 | deploy versioned schemas to your customers. The basic process is as follows: |
1063 | |
da4779ad |
1064 | =over 4 |
1065 | |
1066 | =item 1. |
1067 | |
1068 | Create a DBIx::Class schema |
1069 | |
1070 | =item 2. |
1071 | |
1072 | Save the schema |
1073 | |
1074 | =item 3. |
1075 | |
1076 | Deploy to customers |
1077 | |
1078 | =item 4. |
1079 | |
1080 | Modify schema to change functionality |
1081 | |
1082 | =item 5. |
1083 | |
1084 | Deploy update to customers |
1085 | |
1086 | =back |
362500af |
1087 | |
d2f3e87b |
1088 | B<Create a DBIx::Class schema> |
362500af |
1089 | |
1090 | This can either be done manually, or generated from an existing database as |
d2f3e87b |
1091 | described under L</Creating Schemas From An Existing Database> |
362500af |
1092 | |
d2f3e87b |
1093 | B<Save the schema> |
362500af |
1094 | |
d2f3e87b |
1095 | Call L<DBIx::Class::Schema/create_ddl_dir> as above under L</Creating DDL SQL>. |
362500af |
1096 | |
d2f3e87b |
1097 | B<Deploy to customers> |
362500af |
1098 | |
1099 | There are several ways you could deploy your schema. These are probably |
1100 | beyond the scope of this recipe, but might include: |
1101 | |
da4779ad |
1102 | =over 4 |
1103 | |
1104 | =item 1. |
1105 | |
1106 | Require customer to apply manually using their RDBMS. |
1107 | |
1108 | =item 2. |
1109 | |
1110 | Package along with your app, making database dump/schema update/tests |
362500af |
1111 | all part of your install. |
1112 | |
da4779ad |
1113 | =back |
1114 | |
d2f3e87b |
1115 | B<Modify the schema to change functionality> |
362500af |
1116 | |
264f1571 |
1117 | As your application evolves, it may be necessary to modify your schema |
1118 | to change functionality. Once the changes are made to your schema in |
1119 | DBIx::Class, export the modified schema and the conversion scripts as |
d2f3e87b |
1120 | in L</Creating DDL SQL>. |
362500af |
1121 | |
d2f3e87b |
1122 | B<Deploy update to customers> |
362500af |
1123 | |
264f1571 |
1124 | Add the L<DBIx::Class::Schema::Versioned> schema component to your |
1125 | Schema class. This will add a new table to your database called |
1126 | C<SchemaVersions> which will keep track of which version is installed |
1127 | and warn if the user trys to run a newer schema version than the |
1128 | database thinks it has. |
1129 | |
1130 | Alternatively, you can send the conversion sql scripts to your |
1131 | customers as above. |
362500af |
1132 | |
d2f3e87b |
1133 | =head2 Setting quoting for the generated SQL. |
1134 | |
1135 | If the database contains column names with spaces and/or reserved words, they |
1136 | need to be quoted in the SQL queries. This is done using: |
1137 | |
1138 | __PACKAGE__->storage->sql_maker->quote_char([ qw/[ ]/] ); |
1139 | __PACKAGE__->storage->sql_maker->name_sep('.'); |
1140 | |
1141 | The first sets the quote characters. Either a pair of matching |
1142 | brackets, or a C<"> or C<'>: |
1143 | |
1144 | __PACKAGE__->storage->sql_maker->quote_char('"'); |
1145 | |
1146 | Check the documentation of your database for the correct quote |
1147 | characters to use. C<name_sep> needs to be set to allow the SQL |
1148 | generator to put the quotes the correct place. |
1149 | |
1150 | In most cases you should set these as part of the arguments passed to |
1151 | L<DBIx::Class::Schema/conect>: |
1152 | |
1153 | my $schema = My::Schema->connect( |
1154 | 'dbi:mysql:my_db', |
1155 | 'db_user', |
1156 | 'db_password', |
1157 | { |
1158 | quote_char => '"', |
1159 | name_sep => '.' |
1160 | } |
1161 | ) |
1162 | |
7be93b07 |
1163 | =head2 Setting limit dialect for SQL::Abstract::Limit |
1164 | |
324572ca |
1165 | In some cases, SQL::Abstract::Limit cannot determine the dialect of |
1166 | the remote SQL server by looking at the database handle. This is a |
1167 | common problem when using the DBD::JDBC, since the DBD-driver only |
1168 | know that in has a Java-driver available, not which JDBC driver the |
1169 | Java component has loaded. This specifically sets the limit_dialect |
1170 | to Microsoft SQL-server (See more names in SQL::Abstract::Limit |
1171 | -documentation. |
7be93b07 |
1172 | |
1173 | __PACKAGE__->storage->sql_maker->limit_dialect('mssql'); |
1174 | |
324572ca |
1175 | The JDBC bridge is one way of getting access to a MSSQL server from a platform |
7be93b07 |
1176 | that Microsoft doesn't deliver native client libraries for. (e.g. Linux) |
1177 | |
d2f3e87b |
1178 | The limit dialect can also be set at connect time by specifying a |
1179 | C<limit_dialect> key in the final hash as shown above. |
2437a1e3 |
1180 | |
d2f3e87b |
1181 | =head1 BOOTSTRAPPING/MIGRATING |
2437a1e3 |
1182 | |
d2f3e87b |
1183 | =head2 Easy migration from class-based to schema-based setup |
2437a1e3 |
1184 | |
d2f3e87b |
1185 | You want to start using the schema-based approach to L<DBIx::Class> |
1186 | (see L<SchemaIntro.pod>), but have an established class-based setup with lots |
1187 | of existing classes that you don't want to move by hand. Try this nifty script |
1188 | instead: |
1189 | |
1190 | use MyDB; |
1191 | use SQL::Translator; |
1192 | |
1193 | my $schema = MyDB->schema_instance; |
2437a1e3 |
1194 | |
d2f3e87b |
1195 | my $translator = SQL::Translator->new( |
1196 | debug => $debug || 0, |
1197 | trace => $trace || 0, |
1198 | no_comments => $no_comments || 0, |
1199 | show_warnings => $show_warnings || 0, |
1200 | add_drop_table => $add_drop_table || 0, |
1201 | validate => $validate || 0, |
1202 | parser_args => { |
1203 | 'DBIx::Schema' => $schema, |
1204 | }, |
1205 | producer_args => { |
1206 | 'prefix' => 'My::Schema', |
1207 | }, |
1208 | ); |
1209 | |
1210 | $translator->parser('SQL::Translator::Parser::DBIx::Class'); |
1211 | $translator->producer('SQL::Translator::Producer::DBIx::Class::File'); |
1212 | |
1213 | my $output = $translator->translate(@args) or die |
1214 | "Error: " . $translator->error; |
1215 | |
1216 | print $output; |
2437a1e3 |
1217 | |
d2f3e87b |
1218 | You could use L<Module::Find> to search for all subclasses in the MyDB::* |
1219 | namespace, which is currently left as an exercise for the reader. |
2437a1e3 |
1220 | |
d2f3e87b |
1221 | =head1 OVERLOADING METHODS |
086b93a2 |
1222 | |
ab872312 |
1223 | L<DBIx::Class> uses the L<Class::C3> package, which provides for redispatch of |
1224 | method calls, useful for things like default values and triggers. You have to |
1225 | use calls to C<next::method> to overload methods. More information on using |
1226 | L<Class::C3> with L<DBIx::Class> can be found in |
086b93a2 |
1227 | L<DBIx::Class::Manual::Component>. |
1228 | |
d2f3e87b |
1229 | =head2 Setting default values for a row |
1230 | |
1231 | It's as simple as overriding the C<new> method. Note the use of |
1232 | C<next::method>. |
1233 | |
1234 | sub new { |
1235 | my ( $class, $attrs ) = @_; |
1236 | |
1237 | $attrs->{foo} = 'bar' unless defined $attrs->{foo}; |
1238 | |
1239 | my $new = $class->next::method($attrs); |
1240 | |
1241 | return $new; |
1242 | } |
1243 | |
1244 | For more information about C<next::method>, look in the L<Class::C3> |
1245 | documentation. See also L<DBIx::Class::Manual::Component> for more |
1246 | ways to write your own base classes to do this. |
1247 | |
1248 | People looking for ways to do "triggers" with DBIx::Class are probably |
1249 | just looking for this. |
1250 | |
1251 | =head2 Changing one field whenever another changes |
086b93a2 |
1252 | |
1253 | For example, say that you have three columns, C<id>, C<number>, and |
1254 | C<squared>. You would like to make changes to C<number> and have |
1255 | C<squared> be automagically set to the value of C<number> squared. |
1256 | You can accomplish this by overriding C<store_column>: |
1257 | |
1258 | sub store_column { |
1259 | my ( $self, $name, $value ) = @_; |
1260 | if ($name eq 'number') { |
1261 | $self->squared($value * $value); |
1262 | } |
1263 | $self->next::method($name, $value); |
1264 | } |
1265 | |
1266 | Note that the hard work is done by the call to C<next::method>, which |
324572ca |
1267 | redispatches your call to store_column in the superclass(es). |
086b93a2 |
1268 | |
d2f3e87b |
1269 | =head2 Automatically creating related objects |
086b93a2 |
1270 | |
324572ca |
1271 | You might have a class C<Artist> which has many C<CD>s. Further, if you |
086b93a2 |
1272 | want to create a C<CD> object every time you insert an C<Artist> object. |
ccbebdbc |
1273 | You can accomplish this by overriding C<insert> on your objects: |
086b93a2 |
1274 | |
1275 | sub insert { |
ccbebdbc |
1276 | my ( $self, @args ) = @_; |
1277 | $self->next::method(@args); |
086b93a2 |
1278 | $self->cds->new({})->fill_from_artist($self)->insert; |
1279 | return $self; |
1280 | } |
1281 | |
1282 | where C<fill_from_artist> is a method you specify in C<CD> which sets |
1283 | values in C<CD> based on the data in the C<Artist> object you pass in. |
1284 | |
d2f3e87b |
1285 | =head2 Wrapping/overloading a column accessor |
1286 | |
1287 | B<Problem:> |
1288 | |
1289 | Say you have a table "Camera" and want to associate a description |
1290 | with each camera. For most cameras, you'll be able to generate the description from |
1291 | the other columns. However, in a few special cases you may want to associate a |
1292 | custom description with a camera. |
1293 | |
1294 | B<Solution:> |
1295 | |
1296 | In your database schema, define a description field in the "Camera" table that |
1297 | can contain text and null values. |
1298 | |
1299 | In DBIC, we'll overload the column accessor to provide a sane default if no |
1300 | custom description is defined. The accessor will either return or generate the |
1301 | description, depending on whether the field is null or not. |
1302 | |
1303 | First, in your "Camera" schema class, define the description field as follows: |
1304 | |
1305 | __PACKAGE__->add_columns(description => { accessor => '_description' }); |
1306 | |
1307 | Next, we'll define the accessor-wrapper subroutine: |
1308 | |
1309 | sub description { |
1310 | my $self = shift; |
1311 | |
1312 | # If there is an update to the column, we'll let the original accessor |
1313 | # deal with it. |
1314 | return $self->_description(@_) if @_; |
1315 | |
1316 | # Fetch the column value. |
1317 | my $description = $self->_description; |
1318 | |
1319 | # If there's something in the description field, then just return that. |
1320 | return $description if defined $description && length $descripton; |
1321 | |
1322 | # Otherwise, generate a description. |
1323 | return $self->generate_description; |
1324 | } |
1325 | |
1326 | =head1 DEBUGGING AND PROFILING |
1327 | |
1328 | =head2 DBIx::Class objects with Data::Dumper |
1def3451 |
1329 | |
1330 | L<Data::Dumper> can be a very useful tool for debugging, but sometimes it can |
1331 | be hard to find the pertinent data in all the data it can generate. |
1332 | Specifically, if one naively tries to use it like so, |
1333 | |
1334 | use Data::Dumper; |
1335 | |
1336 | my $cd = $schema->resultset('CD')->find(1); |
1337 | print Dumper($cd); |
1338 | |
1339 | several pages worth of data from the CD object's schema and result source will |
1340 | be dumped to the screen. Since usually one is only interested in a few column |
1341 | values of the object, this is not very helpful. |
1342 | |
1343 | Luckily, it is possible to modify the data before L<Data::Dumper> outputs |
1344 | it. Simply define a hook that L<Data::Dumper> will call on the object before |
1345 | dumping it. For example, |
1346 | |
1347 | package My::DB::CD; |
1348 | |
1349 | sub _dumper_hook { |
99fb1058 |
1350 | $_[0] = bless { |
1351 | %{ $_[0] }, |
1def3451 |
1352 | result_source => undef, |
99fb1058 |
1353 | }, ref($_[0]); |
1def3451 |
1354 | } |
1355 | |
1356 | [...] |
1357 | |
1358 | use Data::Dumper; |
1359 | |
22139027 |
1360 | local $Data::Dumper::Freezer = '_dumper_hook'; |
1def3451 |
1361 | |
1362 | my $cd = $schema->resultset('CD')->find(1); |
1363 | print Dumper($cd); |
1364 | # dumps $cd without its ResultSource |
1365 | |
1366 | If the structure of your schema is such that there is a common base class for |
1367 | all your table classes, simply put a method similar to C<_dumper_hook> in the |
1368 | base class and set C<$Data::Dumper::Freezer> to its name and L<Data::Dumper> |
1369 | will automagically clean up your data before printing it. See |
1370 | L<Data::Dumper/EXAMPLES> for more information. |
1371 | |
4c248161 |
1372 | =head2 Profiling |
1373 | |
85f78622 |
1374 | When you enable L<DBIx::Class::Storage>'s debugging it prints the SQL |
4c248161 |
1375 | executed as well as notifications of query completion and transaction |
1376 | begin/commit. If you'd like to profile the SQL you can subclass the |
1377 | L<DBIx::Class::Storage::Statistics> class and write your own profiling |
1378 | mechanism: |
1379 | |
1380 | package My::Profiler; |
1381 | use strict; |
1382 | |
1383 | use base 'DBIx::Class::Storage::Statistics'; |
1384 | |
1385 | use Time::HiRes qw(time); |
1386 | |
1387 | my $start; |
1388 | |
1389 | sub query_start { |
1390 | my $self = shift(); |
1391 | my $sql = shift(); |
1392 | my $params = @_; |
1393 | |
70f39278 |
1394 | $self->print("Executing $sql: ".join(', ', @params)."\n"); |
4c248161 |
1395 | $start = time(); |
1396 | } |
1397 | |
1398 | sub query_end { |
1399 | my $self = shift(); |
1400 | my $sql = shift(); |
1401 | my @params = @_; |
1402 | |
70f39278 |
1403 | my $elapsed = sprintf("%0.4f", time() - $start); |
1404 | $self->print("Execution took $elapsed seconds.\n"); |
4c248161 |
1405 | $start = undef; |
1406 | } |
1407 | |
1408 | 1; |
1409 | |
1410 | You can then install that class as the debugging object: |
1411 | |
70f39278 |
1412 | __PACKAGE__->storage->debugobj(new My::Profiler()); |
1413 | __PACKAGE__->storage->debug(1); |
4c248161 |
1414 | |
1415 | A more complicated example might involve storing each execution of SQL in an |
1416 | array: |
1417 | |
1418 | sub query_end { |
1419 | my $self = shift(); |
1420 | my $sql = shift(); |
1421 | my @params = @_; |
1422 | |
1423 | my $elapsed = time() - $start; |
1424 | push(@{ $calls{$sql} }, { |
1425 | params => \@params, |
1426 | elapsed => $elapsed |
1427 | }); |
1428 | } |
1429 | |
1430 | You could then create average, high and low execution times for an SQL |
1431 | statement and dig down to see if certain parameters cause aberrant behavior. |
70f39278 |
1432 | You might want to check out L<DBIx::Class::QueryLog> as well. |
4c248161 |
1433 | |
7aaec96c |
1434 | |
40dbc108 |
1435 | =cut |