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1 | =head1 NAME |
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2 | |
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3 | DBIx::Class::Manual::Cookbook - Miscellaneous recipes |
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4 | |
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5 | =head1 RECIPES |
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6 | |
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7 | =head2 Searching |
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8 | |
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9 | =head3 Paged results |
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10 | |
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11 | When you expect a large number of results, you can ask L<DBIx::Class> for a |
12 | paged resultset, which will fetch only a small number of records at a time: |
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13 | |
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14 | my $rs = $schema->resultset('Artist')->search( |
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15 | undef, |
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16 | { |
17 | page => 1, # page to return (defaults to 1) |
18 | rows => 10, # number of results per page |
19 | }, |
20 | ); |
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21 | |
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22 | return $rs->all(); # all records for page 1 |
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23 | |
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24 | The C<page> attribute does not have to be specified in your search: |
25 | |
26 | my $rs = $schema->resultset('Artist')->search( |
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27 | undef, |
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28 | { |
29 | rows => 10, |
30 | } |
31 | ); |
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32 | |
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33 | return $rs->page(1); # DBIx::Class::ResultSet containing first 10 records |
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34 | |
35 | In either of the above cases, you can return a L<Data::Page> object for the |
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36 | resultset (suitable for use in e.g. a template) using the C<pager> method: |
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37 | |
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38 | return $rs->pager(); |
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39 | |
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40 | =head3 Complex WHERE clauses |
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41 | |
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42 | Sometimes you need to formulate a query using specific operators: |
43 | |
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44 | my @albums = $schema->resultset('Album')->search({ |
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45 | artist => { 'like', '%Lamb%' }, |
46 | title => { 'like', '%Fear of Fours%' }, |
47 | }); |
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48 | |
49 | This results in something like the following C<WHERE> clause: |
50 | |
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51 | WHERE artist LIKE '%Lamb%' AND title LIKE '%Fear of Fours%' |
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52 | |
53 | Other queries might require slightly more complex logic: |
54 | |
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55 | my @albums = $schema->resultset('Album')->search({ |
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56 | -or => [ |
57 | -and => [ |
58 | artist => { 'like', '%Smashing Pumpkins%' }, |
59 | title => 'Siamese Dream', |
60 | ], |
61 | artist => 'Starchildren', |
62 | ], |
63 | }); |
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64 | |
65 | This results in the following C<WHERE> clause: |
66 | |
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67 | WHERE ( artist LIKE '%Smashing Pumpkins%' AND title = 'Siamese Dream' ) |
68 | OR artist = 'Starchildren' |
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69 | |
70 | For more information on generating complex queries, see |
71 | L<SQL::Abstract/WHERE CLAUSES>. |
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72 | |
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73 | =head3 Using specific columns |
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74 | |
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75 | When you only want specific columns from a table, you can use |
76 | C<columns> to specify which ones you need. This is useful to avoid |
77 | loading columns with large amounts of data that you aren't about to |
78 | use anyway: |
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79 | |
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80 | my $rs = $schema->resultset('Artist')->search( |
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81 | undef, |
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82 | { |
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83 | columns => [qw/ name /] |
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84 | } |
85 | ); |
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86 | |
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87 | # Equivalent SQL: |
88 | # SELECT artist.name FROM artist |
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89 | |
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90 | This is a shortcut for C<select> and C<as>, see below. C<columns> |
91 | cannot be used together with C<select> and C<as>. |
92 | |
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93 | =head3 Using database functions or stored procedures |
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94 | |
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95 | The combination of C<select> and C<as> can be used to return the result of a |
96 | database function or stored procedure as a column value. You use C<select> to |
97 | specify the source for your column value (e.g. a column name, function, or |
98 | stored procedure name). You then use C<as> to set the column name you will use |
99 | to access the returned value: |
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100 | |
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101 | my $rs = $schema->resultset('Artist')->search( |
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102 | {}, |
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103 | { |
104 | select => [ 'name', { LENGTH => 'name' } ], |
105 | as => [qw/ name name_length /], |
106 | } |
107 | ); |
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108 | |
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109 | # Equivalent SQL: |
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110 | # SELECT name name, LENGTH( name ) |
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111 | # FROM artist |
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112 | |
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113 | Note that the C< as > attribute has absolutely nothing to with the sql |
114 | syntax C< SELECT foo AS bar > (see the documentation in |
115 | L<DBIx::Class::ResultSet/ATTRIBUTES>). If your alias exists as a |
116 | column in your base class (i.e. it was added with C<add_columns>), you |
117 | just access it as normal. Our C<Artist> class has a C<name> column, so |
118 | we just use the C<name> accessor: |
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119 | |
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120 | my $artist = $rs->first(); |
121 | my $name = $artist->name(); |
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122 | |
123 | If on the other hand the alias does not correspond to an existing column, you |
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124 | have to fetch the value using the C<get_column> accessor: |
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125 | |
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126 | my $name_length = $artist->get_column('name_length'); |
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127 | |
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128 | If you don't like using C<get_column>, you can always create an accessor for |
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129 | any of your aliases using either of these: |
130 | |
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131 | # Define accessor manually: |
132 | sub name_length { shift->get_column('name_length'); } |
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133 | |
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134 | # Or use DBIx::Class::AccessorGroup: |
135 | __PACKAGE__->mk_group_accessors('column' => 'name_length'); |
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136 | |
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137 | =head3 SELECT DISTINCT with multiple columns |
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138 | |
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139 | my $rs = $schema->resultset('Foo')->search( |
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140 | {}, |
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141 | { |
142 | select => [ |
143 | { distinct => [ $source->columns ] } |
144 | ], |
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145 | as => [ $source->columns ] # remember 'as' is not the same as SQL AS :-) |
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146 | } |
147 | ); |
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148 | |
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149 | my $count = $rs->next->get_column('count'); |
150 | |
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151 | =head3 SELECT COUNT(DISTINCT colname) |
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152 | |
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153 | my $rs = $schema->resultset('Foo')->search( |
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154 | {}, |
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155 | { |
156 | select => [ |
157 | { count => { distinct => 'colname' } } |
158 | ], |
159 | as => [ 'count' ] |
160 | } |
161 | ); |
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162 | |
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163 | =head3 Grouping results |
164 | |
165 | L<DBIx::Class> supports C<GROUP BY> as follows: |
166 | |
167 | my $rs = $schema->resultset('Artist')->search( |
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168 | {}, |
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169 | { |
170 | join => [qw/ cds /], |
171 | select => [ 'name', { count => 'cds.cdid' } ], |
172 | as => [qw/ name cd_count /], |
173 | group_by => [qw/ name /] |
174 | } |
175 | ); |
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176 | |
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177 | # Equivalent SQL: |
178 | # SELECT name, COUNT( cds.cdid ) FROM artist me |
179 | # LEFT JOIN cd cds ON ( cds.artist = me.artistid ) |
180 | # GROUP BY name |
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181 | |
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182 | Please see L<DBIx::Class::ResultSet/ATTRIBUTES> documentation if you |
183 | are in any way unsure about the use of the attributes above (C< join |
184 | >, C< select >, C< as > and C< group_by >). |
185 | |
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186 | =head3 Predefined searches |
187 | |
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188 | You can write your own L<DBIx::Class::ResultSet> class by inheriting from it |
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189 | and define often used searches as methods: |
190 | |
191 | package My::DBIC::ResultSet::CD; |
192 | use strict; |
193 | use warnings; |
194 | use base 'DBIx::Class::ResultSet'; |
195 | |
196 | sub search_cds_ordered { |
197 | my ($self) = @_; |
198 | |
199 | return $self->search( |
200 | {}, |
201 | { order_by => 'name DESC' }, |
202 | ); |
203 | } |
204 | |
205 | 1; |
206 | |
207 | To use your resultset, first tell DBIx::Class to create an instance of it |
208 | for you, in your My::DBIC::Schema::CD class: |
209 | |
210 | __PACKAGE__->resultset_class('My::DBIC::ResultSet::CD'); |
211 | |
212 | Then call your new method in your code: |
213 | |
214 | my $ordered_cds = $schema->resultset('CD')->search_cds_ordered(); |
215 | |
216 | |
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217 | =head3 Predefined searches without writing a ResultSet class |
218 | |
219 | Alternatively you can automatically generate a DBIx::Class::ResultSet |
220 | class by using the ResultSetManager component and tagging your method |
221 | as ResultSet: |
222 | |
223 | __PACKAGE__->load_components(qw/ ResultSetManager Core /); |
224 | |
225 | sub search_cds_ordered : ResultSet { |
226 | my ($self) = @_; |
227 | return $self->search( |
228 | {}, |
229 | { order_by => 'name DESC' }, |
230 | ); |
231 | } |
232 | |
233 | Then call your method in the same way from your code: |
234 | |
235 | my $ordered_cds = $schema->resultset('CD')->search_cds_ordered(); |
236 | |
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237 | =head2 Using joins and prefetch |
238 | |
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239 | You can use the C<join> attribute to allow searching on, or sorting your |
240 | results by, one or more columns in a related table. To return all CDs matching |
241 | a particular artist name: |
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242 | |
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243 | my $rs = $schema->resultset('CD')->search( |
244 | { |
245 | 'artist.name' => 'Bob Marley' |
246 | }, |
247 | { |
248 | join => [qw/artist/], # join the artist table |
249 | } |
250 | ); |
251 | |
252 | # Equivalent SQL: |
253 | # SELECT cd.* FROM cd |
254 | # JOIN artist ON cd.artist = artist.id |
255 | # WHERE artist.name = 'Bob Marley' |
256 | |
257 | If required, you can now sort on any column in the related tables by including |
258 | it in your C<order_by> attribute: |
259 | |
260 | my $rs = $schema->resultset('CD')->search( |
261 | { |
262 | 'artist.name' => 'Bob Marley' |
263 | }, |
264 | { |
265 | join => [qw/ artist /], |
266 | order_by => [qw/ artist.name /] |
267 | } |
268 | }; |
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269 | |
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270 | # Equivalent SQL: |
271 | # SELECT cd.* FROM cd |
272 | # JOIN artist ON cd.artist = artist.id |
273 | # WHERE artist.name = 'Bob Marley' |
274 | # ORDER BY artist.name |
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275 | |
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276 | Note that the C<join> attribute should only be used when you need to search or |
277 | sort using columns in a related table. Joining related tables when you only |
278 | need columns from the main table will make performance worse! |
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279 | |
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280 | Now let's say you want to display a list of CDs, each with the name of the |
281 | artist. The following will work fine: |
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282 | |
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283 | while (my $cd = $rs->next) { |
284 | print "CD: " . $cd->title . ", Artist: " . $cd->artist->name; |
285 | } |
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286 | |
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287 | There is a problem however. We have searched both the C<cd> and C<artist> tables |
288 | in our main query, but we have only returned data from the C<cd> table. To get |
289 | the artist name for any of the CD objects returned, L<DBIx::Class> will go back |
290 | to the database: |
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291 | |
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292 | SELECT artist.* FROM artist WHERE artist.id = ? |
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293 | |
294 | A statement like the one above will run for each and every CD returned by our |
295 | main query. Five CDs, five extra queries. A hundred CDs, one hundred extra |
296 | queries! |
297 | |
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298 | Thankfully, L<DBIx::Class> has a C<prefetch> attribute to solve this problem. |
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299 | This allows you to fetch results from related tables in advance: |
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300 | |
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301 | my $rs = $schema->resultset('CD')->search( |
302 | { |
303 | 'artist.name' => 'Bob Marley' |
304 | }, |
305 | { |
306 | join => [qw/ artist /], |
307 | order_by => [qw/ artist.name /], |
308 | prefetch => [qw/ artist /] # return artist data too! |
309 | } |
310 | ); |
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311 | |
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312 | # Equivalent SQL (note SELECT from both "cd" and "artist"): |
313 | # SELECT cd.*, artist.* FROM cd |
314 | # JOIN artist ON cd.artist = artist.id |
315 | # WHERE artist.name = 'Bob Marley' |
316 | # ORDER BY artist.name |
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317 | |
318 | The code to print the CD list remains the same: |
319 | |
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320 | while (my $cd = $rs->next) { |
321 | print "CD: " . $cd->title . ", Artist: " . $cd->artist->name; |
322 | } |
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323 | |
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324 | L<DBIx::Class> has now prefetched all matching data from the C<artist> table, |
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325 | so no additional SQL statements are executed. You now have a much more |
326 | efficient query. |
327 | |
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328 | Note that as of L<DBIx::Class> 0.05999_01, C<prefetch> I<can> be used with |
329 | C<has_many> relationships. |
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330 | |
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331 | Also note that C<prefetch> should only be used when you know you will |
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332 | definitely use data from a related table. Pre-fetching related tables when you |
333 | only need columns from the main table will make performance worse! |
334 | |
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335 | =head3 Multi-step joins |
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336 | |
337 | Sometimes you want to join more than one relationship deep. In this example, |
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338 | we want to find all C<Artist> objects who have C<CD>s whose C<LinerNotes> |
339 | contain a specific string: |
340 | |
341 | # Relationships defined elsewhere: |
342 | # Artist->has_many('cds' => 'CD', 'artist'); |
343 | # CD->has_one('liner_notes' => 'LinerNotes', 'cd'); |
344 | |
345 | my $rs = $schema->resultset('Artist')->search( |
346 | { |
347 | 'liner_notes.notes' => { 'like', '%some text%' }, |
348 | }, |
349 | { |
350 | join => { |
351 | 'cds' => 'liner_notes' |
352 | } |
353 | } |
354 | ); |
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355 | |
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356 | # Equivalent SQL: |
357 | # SELECT artist.* FROM artist |
358 | # JOIN ( cd ON artist.id = cd.artist ) |
359 | # JOIN ( liner_notes ON cd.id = liner_notes.cd ) |
360 | # WHERE liner_notes.notes LIKE '%some text%' |
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361 | |
362 | Joins can be nested to an arbitrary level. So if we decide later that we |
363 | want to reduce the number of Artists returned based on who wrote the liner |
364 | notes: |
365 | |
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366 | # Relationship defined elsewhere: |
367 | # LinerNotes->belongs_to('author' => 'Person'); |
368 | |
369 | my $rs = $schema->resultset('Artist')->search( |
370 | { |
371 | 'liner_notes.notes' => { 'like', '%some text%' }, |
372 | 'author.name' => 'A. Writer' |
373 | }, |
374 | { |
375 | join => { |
376 | 'cds' => { |
377 | 'liner_notes' => 'author' |
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378 | } |
bade79c4 |
379 | } |
380 | } |
381 | ); |
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382 | |
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383 | # Equivalent SQL: |
384 | # SELECT artist.* FROM artist |
385 | # JOIN ( cd ON artist.id = cd.artist ) |
386 | # JOIN ( liner_notes ON cd.id = liner_notes.cd ) |
387 | # JOIN ( author ON author.id = liner_notes.author ) |
388 | # WHERE liner_notes.notes LIKE '%some text%' |
389 | # AND author.name = 'A. Writer' |
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390 | |
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391 | =head2 Multi-step prefetch |
392 | |
393 | From 0.04999_05 onwards, C<prefetch> can be nested more than one relationship |
394 | deep using the same syntax as a multi-step join: |
395 | |
396 | my $rs = $schema->resultset('Tag')->search( |
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397 | {}, |
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398 | { |
399 | prefetch => { |
400 | cd => 'artist' |
401 | } |
402 | } |
403 | ); |
404 | |
405 | # Equivalent SQL: |
406 | # SELECT tag.*, cd.*, artist.* FROM tag |
407 | # JOIN cd ON tag.cd = cd.cdid |
408 | # JOIN artist ON cd.artist = artist.artistid |
409 | |
410 | Now accessing our C<cd> and C<artist> relationships does not need additional |
411 | SQL statements: |
412 | |
413 | my $tag = $rs->first; |
414 | print $tag->cd->artist->name; |
415 | |
ac2803ef |
416 | =head2 Columns of data |
417 | |
418 | If you want to find the sum of a particular column there are several |
419 | ways, the obvious one is to use search: |
420 | |
421 | my $rs = $schema->resultset('Items')->search( |
422 | {}, |
423 | { |
424 | select => [ { sum => 'Cost' } ], |
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425 | as => [ 'total_cost' ], # remember this 'as' is for DBIx::Class::ResultSet not SQL |
ac2803ef |
426 | } |
427 | ); |
428 | my $tc = $rs->first->get_column('total_cost'); |
429 | |
430 | Or, you can use the L<DBIx::Class::ResultSetColumn>, which gets |
431 | returned when you ask the C<ResultSet> for a column using |
432 | C<get_column>: |
433 | |
434 | my $cost = $schema->resultset('Items')->get_column('Cost'); |
435 | my $tc = $cost->sum; |
436 | |
437 | With this you can also do: |
438 | |
439 | my $minvalue = $cost->min; |
440 | my $maxvalue = $cost->max; |
441 | |
442 | Or just iterate through the values of this column only: |
443 | |
444 | while ( my $c = $cost->next ) { |
445 | print $c; |
446 | } |
447 | |
448 | foreach my $c ($cost->all) { |
449 | print $c; |
450 | } |
451 | |
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452 | C<ResultSetColumn> only has a limited number of built-in functions, if |
453 | you need one that it doesn't have, then you can use the C<func> method |
454 | instead: |
455 | |
456 | my $avg = $cost->func('AVERAGE'); |
457 | |
458 | This will cause the following SQL statement to be run: |
459 | |
460 | SELECT AVERAGE(Cost) FROM Items me |
461 | |
462 | Which will of course only work if your database supports this function. |
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463 | See L<DBIx::Class::ResultSetColumn> for more documentation. |
464 | |
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465 | =head2 Using relationships |
466 | |
467 | =head3 Create a new row in a related table |
468 | |
469 | my $book->create_related('author', { name => 'Fred'}); |
470 | |
471 | =head3 Search in a related table |
472 | |
473 | Only searches for books named 'Titanic' by the author in $author. |
474 | |
475 | my $author->search_related('books', { name => 'Titanic' }); |
476 | |
477 | =head3 Delete data in a related table |
478 | |
479 | Deletes only the book named Titanic by the author in $author. |
480 | |
481 | my $author->delete_related('books', { name => 'Titanic' }); |
482 | |
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483 | =head3 Ordering a relationship result set |
484 | |
485 | If you always want a relation to be ordered, you can specify this when you |
486 | create the relationship. |
487 | |
488 | To order C<< $book->pages >> by descending page_number. |
489 | |
490 | Book->has_many('pages' => 'Page', 'book', { order_by => \'page_number DESC'} ); |
491 | |
492 | |
493 | |
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494 | =head2 Transactions |
495 | |
496 | As of version 0.04001, there is improved transaction support in |
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497 | L<DBIx::Class::Storage> and L<DBIx::Class::Schema>. Here is an |
181a28f4 |
498 | example of the recommended way to use it: |
87980de7 |
499 | |
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500 | my $genus = $schema->resultset('Genus')->find(12); |
501 | |
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502 | my $coderef2 = sub { |
503 | $genus->extinct(1); |
504 | $genus->update; |
505 | }; |
506 | |
181a28f4 |
507 | my $coderef1 = sub { |
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508 | $genus->add_to_species({ name => 'troglodyte' }); |
509 | $genus->wings(2); |
510 | $genus->update; |
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511 | $schema->txn_do($coderef2); # Can have a nested transaction |
181a28f4 |
512 | return $genus->species; |
513 | }; |
514 | |
181a28f4 |
515 | my $rs; |
516 | eval { |
70634260 |
517 | $rs = $schema->txn_do($coderef1); |
181a28f4 |
518 | }; |
519 | |
520 | if ($@) { # Transaction failed |
521 | die "the sky is falling!" # |
522 | if ($@ =~ /Rollback failed/); # Rollback failed |
523 | |
524 | deal_with_failed_transaction(); |
35d4fe78 |
525 | } |
87980de7 |
526 | |
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527 | Nested transactions will work as expected. That is, only the outermost |
528 | transaction will actually issue a commit to the $dbh, and a rollback |
529 | at any level of any transaction will cause the entire nested |
530 | transaction to fail. Support for savepoints and for true nested |
40dbc108 |
531 | transactions (for databases that support them) will hopefully be added |
532 | in the future. |
ee38fa40 |
533 | |
130c6439 |
534 | =head2 Many-to-many relationships |
ee38fa40 |
535 | |
787d6a29 |
536 | This is straightforward using L<ManyToMany|DBIx::Class::Relationship/many_to_many>: |
ea6309e2 |
537 | |
bade79c4 |
538 | package My::DB; |
539 | # ... set up connection ... |
540 | |
541 | package My::User; |
542 | use base 'My::DB'; |
543 | __PACKAGE__->table('user'); |
544 | __PACKAGE__->add_columns(qw/id name/); |
545 | __PACKAGE__->set_primary_key('id'); |
546 | __PACKAGE__->has_many('user_address' => 'My::UserAddress', 'user'); |
547 | __PACKAGE__->many_to_many('addresses' => 'user_address', 'address'); |
548 | |
549 | package My::UserAddress; |
550 | use base 'My::DB'; |
551 | __PACKAGE__->table('user_address'); |
552 | __PACKAGE__->add_columns(qw/user address/); |
553 | __PACKAGE__->set_primary_key(qw/user address/); |
554 | __PACKAGE__->belongs_to('user' => 'My::User'); |
555 | __PACKAGE__->belongs_to('address' => 'My::Address'); |
556 | |
557 | package My::Address; |
558 | use base 'My::DB'; |
559 | __PACKAGE__->table('address'); |
560 | __PACKAGE__->add_columns(qw/id street town area_code country/); |
561 | __PACKAGE__->set_primary_key('id'); |
562 | __PACKAGE__->has_many('user_address' => 'My::UserAddress', 'address'); |
563 | __PACKAGE__->many_to_many('users' => 'user_address', 'user'); |
564 | |
565 | $rs = $user->addresses(); # get all addresses for a user |
566 | $rs = $address->users(); # get all users for an address |
567 | |
568 | =head2 Setting default values for a row |
a00e1684 |
569 | |
35d4fe78 |
570 | It's as simple as overriding the C<new> method. Note the use of |
40dbc108 |
571 | C<next::method>. |
a00e1684 |
572 | |
35d4fe78 |
573 | sub new { |
574 | my ( $class, $attrs ) = @_; |
40dbc108 |
575 | |
35d4fe78 |
576 | $attrs->{foo} = 'bar' unless defined $attrs->{foo}; |
40dbc108 |
577 | |
df65edd2 |
578 | my $new = $class->next::method($attrs); |
8b50216e |
579 | |
df65edd2 |
580 | return $new; |
35d4fe78 |
581 | } |
a00e1684 |
582 | |
4a3c6354 |
583 | For more information about C<next::method>, look in the L<Class::C3> |
584 | documentation. See also L<DBIx::Class::Manual::Component> for more |
585 | ways to write your own base classes to do this. |
586 | |
587 | People looking for ways to do "triggers" with DBIx::Class are probably |
588 | just looking for this. |
589 | |
25af00d7 |
590 | =head2 Stringification |
591 | |
40dbc108 |
592 | Employ the standard stringification technique by using the C<overload> |
462bb847 |
593 | module. |
594 | |
595 | To make an object stringify itself as a single column, use something |
596 | like this (replace C<foo> with the column/method of your choice): |
25af00d7 |
597 | |
0472cc04 |
598 | use overload '""' => sub { shift->name}, fallback => 1; |
25af00d7 |
599 | |
462bb847 |
600 | For more complex stringification, you can use an anonymous subroutine: |
601 | |
602 | use overload '""' => sub { $_[0]->name . ", " . |
603 | $_[0]->address }, fallback => 1; |
604 | |
324572ca |
605 | =head3 Stringification Example |
462bb847 |
606 | |
607 | Suppose we have two tables: C<Product> and C<Category>. The table |
608 | specifications are: |
609 | |
610 | Product(id, Description, category) |
611 | Category(id, Description) |
612 | |
613 | C<category> is a foreign key into the Category table. |
614 | |
615 | If you have a Product object C<$obj> and write something like |
616 | |
617 | print $obj->category |
618 | |
619 | things will not work as expected. |
620 | |
621 | To obtain, for example, the category description, you should add this |
622 | method to the class defining the Category table: |
623 | |
624 | use overload "" => sub { |
625 | my $self = shift; |
626 | |
627 | return $self->Description; |
77713550 |
628 | }, fallback => 1; |
462bb847 |
629 | |
bade79c4 |
630 | =head2 Disconnecting cleanly |
631 | |
632 | If you find yourself quitting an app with Control-C a lot during |
633 | development, you might like to put the following signal handler in |
634 | your main database class to make sure it disconnects cleanly: |
635 | |
636 | $SIG{INT} = sub { |
6d1bf0a9 |
637 | __PACKAGE__->storage->disconnect; |
bade79c4 |
638 | }; |
639 | |
362500af |
640 | =head2 Schema import/export |
641 | |
642 | This functionality requires you to have L<SQL::Translator> (also known as |
643 | "SQL Fairy") installed. |
644 | |
645 | To create a DBIx::Class schema from an existing database: |
646 | |
647 | sqlt --from DBI |
648 | --to DBIx::Class::File |
649 | --prefix "MySchema" > MySchema.pm |
650 | |
651 | To create a MySQL database from an existing L<DBIx::Class> schema, convert the |
652 | schema to MySQL's dialect of SQL: |
653 | |
54c30987 |
654 | sqlt --from SQL::Translator::Parser::DBIx::Class |
655 | --to MySQL |
656 | --DBIx::Class "MySchema.pm" > Schema1.sql |
362500af |
657 | |
658 | And import using the mysql client: |
659 | |
660 | mysql -h "host" -D "database" -u "user" -p < Schema1.sql |
661 | |
b0a20454 |
662 | =head2 Easy migration from class-based to schema-based setup |
663 | |
664 | You want to start using the schema-based approach to L<DBIx::Class> |
665 | (see L<SchemaIntro.pod>), but have an established class-based setup with lots |
666 | of existing classes that you don't want to move by hand. Try this nifty script |
667 | instead: |
668 | |
669 | use MyDB; |
670 | use SQL::Translator; |
671 | |
672 | my $schema = MyDB->schema_instance; |
673 | |
674 | my $translator = SQL::Translator->new( |
675 | debug => $debug || 0, |
676 | trace => $trace || 0, |
677 | no_comments => $no_comments || 0, |
678 | show_warnings => $show_warnings || 0, |
679 | add_drop_table => $add_drop_table || 0, |
680 | validate => $validate || 0, |
681 | parser_args => { |
682 | 'DBIx::Schema' => $schema, |
c5f36986 |
683 | }, |
b0a20454 |
684 | producer_args => { |
685 | 'prefix' => 'My::Schema', |
c5f36986 |
686 | }, |
b0a20454 |
687 | ); |
688 | |
d240abac |
689 | $translator->parser('SQL::Translator::Parser::DBIx::Class'); |
690 | $translator->producer('SQL::Translator::Producer::DBIx::Class::File'); |
b0a20454 |
691 | |
692 | my $output = $translator->translate(@args) or die |
693 | "Error: " . $translator->error; |
694 | |
695 | print $output; |
696 | |
697 | You could use L<Module::Find> to search for all subclasses in the MyDB::* |
880a1a0c |
698 | namespace, which is currently left as an exercise for the reader. |
b0a20454 |
699 | |
362500af |
700 | =head2 Schema versioning |
701 | |
702 | The following example shows simplistically how you might use DBIx::Class to |
703 | deploy versioned schemas to your customers. The basic process is as follows: |
704 | |
da4779ad |
705 | =over 4 |
706 | |
707 | =item 1. |
708 | |
709 | Create a DBIx::Class schema |
710 | |
711 | =item 2. |
712 | |
713 | Save the schema |
714 | |
715 | =item 3. |
716 | |
717 | Deploy to customers |
718 | |
719 | =item 4. |
720 | |
721 | Modify schema to change functionality |
722 | |
723 | =item 5. |
724 | |
725 | Deploy update to customers |
726 | |
727 | =back |
362500af |
728 | |
729 | =head3 Create a DBIx::Class schema |
730 | |
731 | This can either be done manually, or generated from an existing database as |
732 | described under C<Schema import/export>. |
733 | |
734 | =head3 Save the schema |
735 | |
736 | Use C<sqlt> to transform your schema into an SQL script suitable for your |
737 | customer's database. E.g. for MySQL: |
738 | |
54c30987 |
739 | sqlt --from SQL::Translator::Parser::DBIx::Class |
362500af |
740 | --to MySQL |
741 | --DBIx::Class "MySchema.pm" > Schema1.mysql.sql |
742 | |
743 | If you need to target databases from multiple vendors, just generate an SQL |
744 | script suitable for each. To support PostgreSQL too: |
745 | |
54c30987 |
746 | sqlt --from SQL::Translator::DBIx::Class |
362500af |
747 | --to PostgreSQL |
748 | --DBIx::Class "MySchema.pm" > Schema1.pgsql.sql |
749 | |
750 | =head3 Deploy to customers |
751 | |
752 | There are several ways you could deploy your schema. These are probably |
753 | beyond the scope of this recipe, but might include: |
754 | |
da4779ad |
755 | =over 4 |
756 | |
757 | =item 1. |
758 | |
759 | Require customer to apply manually using their RDBMS. |
760 | |
761 | =item 2. |
762 | |
763 | Package along with your app, making database dump/schema update/tests |
362500af |
764 | all part of your install. |
765 | |
da4779ad |
766 | =back |
767 | |
362500af |
768 | =head3 Modify the schema to change functionality |
769 | |
770 | As your application evolves, it may be necessary to modify your schema to |
771 | change functionality. Once the changes are made to your schema in DBIx::Class, |
772 | export the modified schema as before, taking care not to overwrite the original: |
773 | |
54c30987 |
774 | sqlt --from SQL::Translator::DBIx::Class |
362500af |
775 | --to MySQL |
776 | --DBIx::Class "Anything.pm" > Schema2.mysql.sql |
777 | |
778 | Next, use sqlt-diff to create an SQL script that will update the customer's |
779 | database schema: |
780 | |
781 | sqlt-diff --to MySQL Schema1=MySQL Schema2=MySQL > SchemaUpdate.mysql.sql |
782 | |
783 | =head3 Deploy update to customers |
784 | |
785 | The schema update can be deployed to customers using the same method as before. |
786 | |
7be93b07 |
787 | =head2 Setting limit dialect for SQL::Abstract::Limit |
788 | |
324572ca |
789 | In some cases, SQL::Abstract::Limit cannot determine the dialect of |
790 | the remote SQL server by looking at the database handle. This is a |
791 | common problem when using the DBD::JDBC, since the DBD-driver only |
792 | know that in has a Java-driver available, not which JDBC driver the |
793 | Java component has loaded. This specifically sets the limit_dialect |
794 | to Microsoft SQL-server (See more names in SQL::Abstract::Limit |
795 | -documentation. |
7be93b07 |
796 | |
797 | __PACKAGE__->storage->sql_maker->limit_dialect('mssql'); |
798 | |
324572ca |
799 | The JDBC bridge is one way of getting access to a MSSQL server from a platform |
7be93b07 |
800 | that Microsoft doesn't deliver native client libraries for. (e.g. Linux) |
801 | |
324572ca |
802 | =head2 Setting quoting for the generated SQL. |
2437a1e3 |
803 | |
324572ca |
804 | If the database contains column names with spaces and/or reserved words, they |
805 | need to be quoted in the SQL queries. This is done using: |
2437a1e3 |
806 | |
807 | __PACKAGE__->storage->sql_maker->quote_char([ qw/[ ]/] ); |
808 | __PACKAGE__->storage->sql_maker->name_sep('.'); |
809 | |
324572ca |
810 | The first sets the quote characters. Either a pair of matching |
811 | brackets, or a C<"> or C<'>: |
2437a1e3 |
812 | |
813 | __PACKAGE__->storage->sql_maker->quote_char('"'); |
814 | |
324572ca |
815 | Check the documentation of your database for the correct quote |
816 | characters to use. C<name_sep> needs to be set to allow the SQL |
817 | generator to put the quotes the correct place. |
2437a1e3 |
818 | |
086b93a2 |
819 | =head2 Overloading methods |
820 | |
821 | L<DBIx::Class> uses the L<Class::C3> package, which provides for redispatch of |
822 | method calls. You have to use calls to C<next::method> to overload methods. |
823 | More information on using L<Class::C3> with L<DBIx::Class> can be found in |
824 | L<DBIx::Class::Manual::Component>. |
825 | |
826 | =head3 Changing one field whenever another changes |
827 | |
828 | For example, say that you have three columns, C<id>, C<number>, and |
829 | C<squared>. You would like to make changes to C<number> and have |
830 | C<squared> be automagically set to the value of C<number> squared. |
831 | You can accomplish this by overriding C<store_column>: |
832 | |
833 | sub store_column { |
834 | my ( $self, $name, $value ) = @_; |
835 | if ($name eq 'number') { |
836 | $self->squared($value * $value); |
837 | } |
838 | $self->next::method($name, $value); |
839 | } |
840 | |
841 | Note that the hard work is done by the call to C<next::method>, which |
324572ca |
842 | redispatches your call to store_column in the superclass(es). |
086b93a2 |
843 | |
844 | =head3 Automatically creating related objects |
845 | |
324572ca |
846 | You might have a class C<Artist> which has many C<CD>s. Further, if you |
086b93a2 |
847 | want to create a C<CD> object every time you insert an C<Artist> object. |
ccbebdbc |
848 | You can accomplish this by overriding C<insert> on your objects: |
086b93a2 |
849 | |
850 | sub insert { |
ccbebdbc |
851 | my ( $self, @args ) = @_; |
852 | $self->next::method(@args); |
086b93a2 |
853 | $self->cds->new({})->fill_from_artist($self)->insert; |
854 | return $self; |
855 | } |
856 | |
857 | where C<fill_from_artist> is a method you specify in C<CD> which sets |
858 | values in C<CD> based on the data in the C<Artist> object you pass in. |
859 | |
1def3451 |
860 | =head2 Debugging DBIx::Class objects with Data::Dumper |
861 | |
862 | L<Data::Dumper> can be a very useful tool for debugging, but sometimes it can |
863 | be hard to find the pertinent data in all the data it can generate. |
864 | Specifically, if one naively tries to use it like so, |
865 | |
866 | use Data::Dumper; |
867 | |
868 | my $cd = $schema->resultset('CD')->find(1); |
869 | print Dumper($cd); |
870 | |
871 | several pages worth of data from the CD object's schema and result source will |
872 | be dumped to the screen. Since usually one is only interested in a few column |
873 | values of the object, this is not very helpful. |
874 | |
875 | Luckily, it is possible to modify the data before L<Data::Dumper> outputs |
876 | it. Simply define a hook that L<Data::Dumper> will call on the object before |
877 | dumping it. For example, |
878 | |
879 | package My::DB::CD; |
880 | |
881 | sub _dumper_hook { |
99fb1058 |
882 | $_[0] = bless { |
883 | %{ $_[0] }, |
1def3451 |
884 | result_source => undef, |
99fb1058 |
885 | }, ref($_[0]); |
1def3451 |
886 | } |
887 | |
888 | [...] |
889 | |
890 | use Data::Dumper; |
891 | |
22139027 |
892 | local $Data::Dumper::Freezer = '_dumper_hook'; |
1def3451 |
893 | |
894 | my $cd = $schema->resultset('CD')->find(1); |
895 | print Dumper($cd); |
896 | # dumps $cd without its ResultSource |
897 | |
898 | If the structure of your schema is such that there is a common base class for |
899 | all your table classes, simply put a method similar to C<_dumper_hook> in the |
900 | base class and set C<$Data::Dumper::Freezer> to its name and L<Data::Dumper> |
901 | will automagically clean up your data before printing it. See |
902 | L<Data::Dumper/EXAMPLES> for more information. |
903 | |
1def3451 |
904 | =head2 Retrieving a row object's Schema |
905 | |
324572ca |
906 | It is possible to get a Schema object from a row object like so: |
1def3451 |
907 | |
908 | my $schema = $cd->result_source->schema; |
324572ca |
909 | # use the schema as normal: |
910 | my $artist_rs = $schema->resultset('Artist'); |
1def3451 |
911 | |
912 | This can be useful when you don't want to pass around a Schema object to every |
913 | method. |
914 | |
4c248161 |
915 | =head2 Profiling |
916 | |
85f78622 |
917 | When you enable L<DBIx::Class::Storage>'s debugging it prints the SQL |
4c248161 |
918 | executed as well as notifications of query completion and transaction |
919 | begin/commit. If you'd like to profile the SQL you can subclass the |
920 | L<DBIx::Class::Storage::Statistics> class and write your own profiling |
921 | mechanism: |
922 | |
923 | package My::Profiler; |
924 | use strict; |
925 | |
926 | use base 'DBIx::Class::Storage::Statistics'; |
927 | |
928 | use Time::HiRes qw(time); |
929 | |
930 | my $start; |
931 | |
932 | sub query_start { |
933 | my $self = shift(); |
934 | my $sql = shift(); |
935 | my $params = @_; |
936 | |
937 | print "Executing $sql: ".join(', ', @params)."\n"; |
938 | $start = time(); |
939 | } |
940 | |
941 | sub query_end { |
942 | my $self = shift(); |
943 | my $sql = shift(); |
944 | my @params = @_; |
945 | |
946 | printf("Execution took %0.4f seconds.\n", time() - $start); |
947 | $start = undef; |
948 | } |
949 | |
950 | 1; |
951 | |
952 | You can then install that class as the debugging object: |
953 | |
954 | __PACKAGE__->storage()->debugobj(new My::Profiler()); |
955 | __PACKAGE__->storage()->debug(1); |
956 | |
957 | A more complicated example might involve storing each execution of SQL in an |
958 | array: |
959 | |
960 | sub query_end { |
961 | my $self = shift(); |
962 | my $sql = shift(); |
963 | my @params = @_; |
964 | |
965 | my $elapsed = time() - $start; |
966 | push(@{ $calls{$sql} }, { |
967 | params => \@params, |
968 | elapsed => $elapsed |
969 | }); |
970 | } |
971 | |
972 | You could then create average, high and low execution times for an SQL |
973 | statement and dig down to see if certain parameters cause aberrant behavior. |
974 | |
e8e9e5c7 |
975 | =head2 Getting the value of the primary key for the last database insert |
976 | |
74413b83 |
977 | AKA getting last_insert_id |
978 | |
e8e9e5c7 |
979 | If you are using PK::Auto, this is straightforward: |
980 | |
74413b83 |
981 | my $foo = $rs->create(\%blah); |
e8e9e5c7 |
982 | # do more stuff |
983 | my $id = $foo->id; # foo->my_primary_key_field will also work. |
984 | |
985 | If you are not using autoincrementing primary keys, this will probably |
986 | not work, but then you already know the value of the last primary key anyway. |
987 | |
824f4422 |
988 | =head2 Dynamic Sub-classing DBIx::Class proxy classes |
989 | (AKA multi-class object inflation from one table) |
990 | |
324572ca |
991 | L<DBIx::Class> classes are proxy classes, therefore some different |
992 | techniques need to be employed for more than basic subclassing. In |
993 | this example we have a single user table that carries a boolean bit |
994 | for admin. We would like like to give the admin users |
995 | objects(L<DBIx::Class::Row>) the same methods as a regular user but |
996 | also special admin only methods. It doesn't make sense to create two |
997 | seperate proxy-class files for this. We would be copying all the user |
998 | methods into the Admin class. There is a cleaner way to accomplish |
999 | this. |
1000 | |
c6d147b6 |
1001 | Overriding the C<inflate_result> method within the User proxy-class |
324572ca |
1002 | gives us the effect we want. This method is called by |
1003 | L<DBIx::Class::ResultSet> when inflating a result from storage. So we |
1004 | grab the object being returned, inspect the values we are looking for, |
1005 | bless it if it's an admin object, and then return it. See the example |
1006 | below: |
824f4422 |
1007 | |
1008 | B<Schema Definition> |
1009 | |
1010 | package DB::Schema; |
1011 | |
1012 | use base qw/DBIx::Class::Schema/; |
1013 | |
1014 | __PACKAGE__->load_classes(qw/User/); |
1015 | |
1016 | |
1017 | B<Proxy-Class definitions> |
1018 | |
1019 | package DB::Schema::User; |
1020 | |
1021 | use strict; |
1022 | use warnings; |
1023 | use base qw/DBIx::Class/; |
1024 | |
1025 | ### Defined what our admin class is for ensure_class_loaded |
1026 | my $admin_class = __PACKAGE__ . '::Admin'; |
1027 | |
324572ca |
1028 | __PACKAGE__->load_components(qw/Core/); |
824f4422 |
1029 | |
1030 | __PACKAGE__->table('users'); |
1031 | |
1032 | __PACKAGE__->add_columns(qw/user_id email password |
1033 | firstname lastname active |
1034 | admin/); |
1035 | |
1036 | __PACKAGE__->set_primary_key('user_id'); |
1037 | |
1038 | sub inflate_result { |
1039 | my $self = shift; |
1040 | my $ret = $self->next::method(@_); |
1041 | if( $ret->admin ) {### If this is an admin rebless for extra functions |
1042 | $self->ensure_class_loaded( $admin_class ); |
1043 | bless $ret, $admin_class; |
1044 | } |
1045 | return $ret; |
1046 | } |
1047 | |
1048 | sub hello { |
1049 | print "I am a regular user.\n"; |
1050 | return ; |
1051 | } |
1052 | |
1053 | |
1054 | package DB::Schema::User::Admin; |
1055 | |
1056 | use strict; |
1057 | use warnings; |
1058 | use base qw/DB::Schema::User/; |
1059 | |
1060 | sub hello |
1061 | { |
1062 | print "I am an admin.\n"; |
1063 | return; |
1064 | } |
1065 | |
1066 | sub do_admin_stuff |
1067 | { |
1068 | print "I am doing admin stuff\n"; |
1069 | return ; |
1070 | } |
1071 | |
1072 | B<Test File> test.pl |
1073 | |
1074 | use warnings; |
1075 | use strict; |
1076 | use DB::Schema; |
1077 | |
1078 | my $user_data = { email => 'someguy@place.com', |
1079 | password => 'pass1', |
1080 | admin => 0 }; |
1081 | |
1082 | my $admin_data = { email => 'someadmin@adminplace.com', |
1083 | password => 'pass2', |
1084 | admin => 1 }; |
1085 | |
1086 | my $schema = DB::Schema->connection('dbi:Pg:dbname=test'); |
1087 | |
1088 | $schema->resultset('User')->create( $user_data ); |
1089 | $schema->resultset('User')->create( $admin_data ); |
1090 | |
1091 | ### Now we search for them |
1092 | my $user = $schema->resultset('User')->single( $user_data ); |
1093 | my $admin = $schema->resultset('User')->single( $admin_data ); |
1094 | |
1095 | print ref $user, "\n"; |
1096 | print ref $admin, "\n"; |
1097 | |
1098 | print $user->password , "\n"; # pass1 |
1099 | print $admin->password , "\n";# pass2; inherited from User |
1100 | print $user->hello , "\n";# I am a regular user. |
1101 | print $admin->hello, "\n";# I am an admin. |
1102 | |
1103 | ### The statement below will NOT print |
1104 | print "I can do admin stuff\n" if $user->can('do_admin_stuff'); |
1105 | ### The statement below will print |
1106 | print "I can do admin stuff\n" if $admin->can('do_admin_stuff'); |
1107 | |
fe5cf259 |
1108 | =head2 Skip object creation for faster results |
1109 | |
1110 | DBIx::Class is not built for speed, it's built for convenience and |
1111 | ease of use, but sometimes you just need to get the data, and skip the |
137c657c |
1112 | fancy objects. |
1113 | |
1114 | To do this simply use L<DBIx::Class::ResultClass::HashRefInflator>. |
1115 | |
1116 | my $rs = $schema->resultset('CD'); |
1117 | |
1118 | $rs->result_class('DBIx::Class::ResultClass::HashRefInflator'); |
1119 | |
1120 | my $hash_ref = $rs->find(1); |
1121 | |
1122 | Wasn't that easy? |
1123 | |
685dad64 |
1124 | =head2 Get raw data for blindingly fast results |
1125 | |
1126 | If the C<inflate_result> solution above is not fast enough for you, you |
1127 | can use a DBIx::Class to return values exactly as they come out of the |
1128 | data base with none of the convenience methods wrapped round them. |
1129 | |
1130 | This is used like so:- |
1131 | |
1132 | my $cursor = $rs->cursor |
1133 | while (my @vals = $cursor->next) { |
1134 | # use $val[0..n] here |
1135 | } |
1136 | |
1137 | You will need to map the array offsets to particular columns (you can |
1138 | use the I<select> attribute of C<search()> to force ordering). |
1139 | |
9e4c2514 |
1140 | =head2 Want to know if find_or_create found or created a row? |
1141 | |
1142 | Just use C<find_or_new> instead, then check C<in_storage>: |
fe5cf259 |
1143 | |
9e4c2514 |
1144 | my $obj = $rs->find_or_new({ blah => 'blarg' }); |
1145 | unless ($obj->in_storage) { |
1146 | $obj->insert; |
1147 | # do whatever else you wanted if it was a new row |
1148 | } |
1149 | |
7aaec96c |
1150 | =head3 Wrapping/overloading a column accessor |
1151 | |
1152 | Problem: Say you have a table "Camera" and want to associate a description |
1153 | with each camera. For most cameras, you'll be able to generate the description from |
1154 | the other columns. However, in a few special cases you may want to associate a |
1155 | custom description with a camera. |
1156 | |
1157 | Solution: |
1158 | |
1159 | In your database schema, define a description field in the "Camera" table that |
1160 | can contain text and null values. |
1161 | |
1162 | In DBIC, we'll overload the column accessor to provide a sane default if no |
1163 | custom description is defined. The accessor will either return or generate the |
1164 | description, depending on whether the field is null or not. |
1165 | |
1166 | First, in your "Camera" schema class, define the description field as follows: |
1167 | |
1168 | __PACKAGE__->add_columns(description => { accessor => '_description' }); |
1169 | |
1170 | Next, we'll define the accessor-wrapper subroutine: |
1171 | |
1172 | sub description { |
1173 | my $self = shift; |
1174 | |
1175 | # If there is an update to the column, we'll let the original accessor |
1176 | # deal with it. |
1177 | return $self->_description(@_) if @_; |
1178 | |
1179 | # Fetch the column value. |
1180 | my $description = $self->_description; |
1181 | |
1182 | # If there's something in the description field, then just return that. |
1183 | return $description if defined $description && length $descripton; |
1184 | |
1185 | # Otherwise, generate a description. |
1186 | return $self->generate_description; |
1187 | } |
1188 | |
40dbc108 |
1189 | =cut |