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