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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 | |
87980de7 |
422 | =head2 Transactions |
423 | |
424 | As of version 0.04001, there is improved transaction support in |
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425 | L<DBIx::Class::Storage::DBI> and L<DBIx::Class::Schema>. Here is an |
426 | example of the recommended way to use it: |
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427 | |
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428 | my $genus = $schema->resultset('Genus')->find(12); |
429 | |
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430 | my $coderef2 = sub { |
431 | $genus->extinct(1); |
432 | $genus->update; |
433 | }; |
434 | |
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435 | my $coderef1 = sub { |
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436 | $genus->add_to_species({ name => 'troglodyte' }); |
437 | $genus->wings(2); |
438 | $genus->update; |
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439 | $schema->txn_do($coderef2); # Can have a nested transaction |
181a28f4 |
440 | return $genus->species; |
441 | }; |
442 | |
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443 | my $rs; |
444 | eval { |
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445 | $rs = $schema->txn_do($coderef1); |
181a28f4 |
446 | }; |
447 | |
448 | if ($@) { # Transaction failed |
449 | die "the sky is falling!" # |
450 | if ($@ =~ /Rollback failed/); # Rollback failed |
451 | |
452 | deal_with_failed_transaction(); |
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453 | } |
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454 | |
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455 | Nested transactions will work as expected. That is, only the outermost |
456 | transaction will actually issue a commit to the $dbh, and a rollback |
457 | at any level of any transaction will cause the entire nested |
458 | transaction to fail. Support for savepoints and for true nested |
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459 | transactions (for databases that support them) will hopefully be added |
460 | in the future. |
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461 | |
130c6439 |
462 | =head2 Many-to-many relationships |
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463 | |
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464 | This is straightforward using L<DBIx::Class::Relationship::ManyToMany>: |
465 | |
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466 | package My::DB; |
467 | # ... set up connection ... |
468 | |
469 | package My::User; |
470 | use base 'My::DB'; |
471 | __PACKAGE__->table('user'); |
472 | __PACKAGE__->add_columns(qw/id name/); |
473 | __PACKAGE__->set_primary_key('id'); |
474 | __PACKAGE__->has_many('user_address' => 'My::UserAddress', 'user'); |
475 | __PACKAGE__->many_to_many('addresses' => 'user_address', 'address'); |
476 | |
477 | package My::UserAddress; |
478 | use base 'My::DB'; |
479 | __PACKAGE__->table('user_address'); |
480 | __PACKAGE__->add_columns(qw/user address/); |
481 | __PACKAGE__->set_primary_key(qw/user address/); |
482 | __PACKAGE__->belongs_to('user' => 'My::User'); |
483 | __PACKAGE__->belongs_to('address' => 'My::Address'); |
484 | |
485 | package My::Address; |
486 | use base 'My::DB'; |
487 | __PACKAGE__->table('address'); |
488 | __PACKAGE__->add_columns(qw/id street town area_code country/); |
489 | __PACKAGE__->set_primary_key('id'); |
490 | __PACKAGE__->has_many('user_address' => 'My::UserAddress', 'address'); |
491 | __PACKAGE__->many_to_many('users' => 'user_address', 'user'); |
492 | |
493 | $rs = $user->addresses(); # get all addresses for a user |
494 | $rs = $address->users(); # get all users for an address |
495 | |
496 | =head2 Setting default values for a row |
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497 | |
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498 | It's as simple as overriding the C<new> method. Note the use of |
40dbc108 |
499 | C<next::method>. |
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500 | |
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501 | sub new { |
502 | my ( $class, $attrs ) = @_; |
40dbc108 |
503 | |
35d4fe78 |
504 | $attrs->{foo} = 'bar' unless defined $attrs->{foo}; |
40dbc108 |
505 | |
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506 | $class->next::method($attrs); |
507 | } |
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508 | |
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509 | For more information about C<next::method>, look in the L<Class::C3> |
510 | documentation. See also L<DBIx::Class::Manual::Component> for more |
511 | ways to write your own base classes to do this. |
512 | |
513 | People looking for ways to do "triggers" with DBIx::Class are probably |
514 | just looking for this. |
515 | |
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516 | =head2 Stringification |
517 | |
40dbc108 |
518 | Employ the standard stringification technique by using the C<overload> |
35d4fe78 |
519 | module. Replace C<foo> with the column/method of your choice. |
25af00d7 |
520 | |
35d4fe78 |
521 | use overload '""' => 'foo', fallback => 1; |
25af00d7 |
522 | |
bade79c4 |
523 | =head2 Disconnecting cleanly |
524 | |
525 | If you find yourself quitting an app with Control-C a lot during |
526 | development, you might like to put the following signal handler in |
527 | your main database class to make sure it disconnects cleanly: |
528 | |
529 | $SIG{INT} = sub { |
6d1bf0a9 |
530 | __PACKAGE__->storage->disconnect; |
bade79c4 |
531 | }; |
532 | |
362500af |
533 | =head2 Schema import/export |
534 | |
535 | This functionality requires you to have L<SQL::Translator> (also known as |
536 | "SQL Fairy") installed. |
537 | |
538 | To create a DBIx::Class schema from an existing database: |
539 | |
540 | sqlt --from DBI |
541 | --to DBIx::Class::File |
542 | --prefix "MySchema" > MySchema.pm |
543 | |
544 | To create a MySQL database from an existing L<DBIx::Class> schema, convert the |
545 | schema to MySQL's dialect of SQL: |
546 | |
547 | sqlt --from DBIx::Class --to MySQL --DBIx::Class "MySchema.pm" > Schema1.sql |
548 | |
549 | And import using the mysql client: |
550 | |
551 | mysql -h "host" -D "database" -u "user" -p < Schema1.sql |
552 | |
b0a20454 |
553 | =head2 Easy migration from class-based to schema-based setup |
554 | |
555 | You want to start using the schema-based approach to L<DBIx::Class> |
556 | (see L<SchemaIntro.pod>), but have an established class-based setup with lots |
557 | of existing classes that you don't want to move by hand. Try this nifty script |
558 | instead: |
559 | |
560 | use MyDB; |
561 | use SQL::Translator; |
562 | |
563 | my $schema = MyDB->schema_instance; |
564 | |
565 | my $translator = SQL::Translator->new( |
566 | debug => $debug || 0, |
567 | trace => $trace || 0, |
568 | no_comments => $no_comments || 0, |
569 | show_warnings => $show_warnings || 0, |
570 | add_drop_table => $add_drop_table || 0, |
571 | validate => $validate || 0, |
572 | parser_args => { |
573 | 'DBIx::Schema' => $schema, |
c5f36986 |
574 | }, |
b0a20454 |
575 | producer_args => { |
576 | 'prefix' => 'My::Schema', |
c5f36986 |
577 | }, |
b0a20454 |
578 | ); |
579 | |
d240abac |
580 | $translator->parser('SQL::Translator::Parser::DBIx::Class'); |
581 | $translator->producer('SQL::Translator::Producer::DBIx::Class::File'); |
b0a20454 |
582 | |
583 | my $output = $translator->translate(@args) or die |
584 | "Error: " . $translator->error; |
585 | |
586 | print $output; |
587 | |
588 | You could use L<Module::Find> to search for all subclasses in the MyDB::* |
880a1a0c |
589 | namespace, which is currently left as an exercise for the reader. |
b0a20454 |
590 | |
362500af |
591 | =head2 Schema versioning |
592 | |
593 | The following example shows simplistically how you might use DBIx::Class to |
594 | deploy versioned schemas to your customers. The basic process is as follows: |
595 | |
da4779ad |
596 | =over 4 |
597 | |
598 | =item 1. |
599 | |
600 | Create a DBIx::Class schema |
601 | |
602 | =item 2. |
603 | |
604 | Save the schema |
605 | |
606 | =item 3. |
607 | |
608 | Deploy to customers |
609 | |
610 | =item 4. |
611 | |
612 | Modify schema to change functionality |
613 | |
614 | =item 5. |
615 | |
616 | Deploy update to customers |
617 | |
618 | =back |
362500af |
619 | |
620 | =head3 Create a DBIx::Class schema |
621 | |
622 | This can either be done manually, or generated from an existing database as |
623 | described under C<Schema import/export>. |
624 | |
625 | =head3 Save the schema |
626 | |
627 | Use C<sqlt> to transform your schema into an SQL script suitable for your |
628 | customer's database. E.g. for MySQL: |
629 | |
630 | sqlt --from DBIx::Class |
631 | --to MySQL |
632 | --DBIx::Class "MySchema.pm" > Schema1.mysql.sql |
633 | |
634 | If you need to target databases from multiple vendors, just generate an SQL |
635 | script suitable for each. To support PostgreSQL too: |
636 | |
637 | sqlt --from DBIx::Class |
638 | --to PostgreSQL |
639 | --DBIx::Class "MySchema.pm" > Schema1.pgsql.sql |
640 | |
641 | =head3 Deploy to customers |
642 | |
643 | There are several ways you could deploy your schema. These are probably |
644 | beyond the scope of this recipe, but might include: |
645 | |
da4779ad |
646 | =over 4 |
647 | |
648 | =item 1. |
649 | |
650 | Require customer to apply manually using their RDBMS. |
651 | |
652 | =item 2. |
653 | |
654 | Package along with your app, making database dump/schema update/tests |
362500af |
655 | all part of your install. |
656 | |
da4779ad |
657 | =back |
658 | |
362500af |
659 | =head3 Modify the schema to change functionality |
660 | |
661 | As your application evolves, it may be necessary to modify your schema to |
662 | change functionality. Once the changes are made to your schema in DBIx::Class, |
663 | export the modified schema as before, taking care not to overwrite the original: |
664 | |
665 | sqlt --from DBIx::Class |
666 | --to MySQL |
667 | --DBIx::Class "Anything.pm" > Schema2.mysql.sql |
668 | |
669 | Next, use sqlt-diff to create an SQL script that will update the customer's |
670 | database schema: |
671 | |
672 | sqlt-diff --to MySQL Schema1=MySQL Schema2=MySQL > SchemaUpdate.mysql.sql |
673 | |
674 | =head3 Deploy update to customers |
675 | |
676 | The schema update can be deployed to customers using the same method as before. |
677 | |
7be93b07 |
678 | =head2 Setting limit dialect for SQL::Abstract::Limit |
679 | |
680 | In some cases, SQL::Abstract::Limit cannot determine the dialect of the remote |
681 | SQL-server by looking at the database-handle. This is a common problem when |
682 | using the DBD::JDBC, since the DBD-driver only know that in has a Java-driver |
683 | available, not which JDBC-driver the Java component has loaded. |
684 | This specifically sets the limit_dialect to Microsoft SQL-server (Se more names |
685 | in SQL::Abstract::Limit -documentation. |
686 | |
687 | __PACKAGE__->storage->sql_maker->limit_dialect('mssql'); |
688 | |
689 | The JDBC-bridge is one way of getting access to a MSSQL-server from a platform |
690 | that Microsoft doesn't deliver native client libraries for. (e.g. Linux) |
691 | |
2437a1e3 |
692 | =head2 Setting quotes for the generated SQL. |
693 | |
694 | If the database contains columnames with spaces and/or reserved words, the |
695 | SQL-query needs to be quoted. This is done using: |
696 | |
697 | __PACKAGE__->storage->sql_maker->quote_char([ qw/[ ]/] ); |
698 | __PACKAGE__->storage->sql_maker->name_sep('.'); |
699 | |
700 | The first sets the quotesymbols. If the quote i "symmetric" as " or ' |
701 | |
702 | __PACKAGE__->storage->sql_maker->quote_char('"'); |
703 | |
880a1a0c |
704 | is enough. If the left quote differs form the right quote, the first |
2437a1e3 |
705 | notation should be used. name_sep needs to be set to allow the |
706 | SQL generator to put the quotes the correct place. |
707 | |
086b93a2 |
708 | =head2 Overloading methods |
709 | |
710 | L<DBIx::Class> uses the L<Class::C3> package, which provides for redispatch of |
711 | method calls. You have to use calls to C<next::method> to overload methods. |
712 | More information on using L<Class::C3> with L<DBIx::Class> can be found in |
713 | L<DBIx::Class::Manual::Component>. |
714 | |
715 | =head3 Changing one field whenever another changes |
716 | |
717 | For example, say that you have three columns, C<id>, C<number>, and |
718 | C<squared>. You would like to make changes to C<number> and have |
719 | C<squared> be automagically set to the value of C<number> squared. |
720 | You can accomplish this by overriding C<store_column>: |
721 | |
722 | sub store_column { |
723 | my ( $self, $name, $value ) = @_; |
724 | if ($name eq 'number') { |
725 | $self->squared($value * $value); |
726 | } |
727 | $self->next::method($name, $value); |
728 | } |
729 | |
730 | Note that the hard work is done by the call to C<next::method>, which |
731 | redispatches your call to store_column to the superclass(es). |
732 | |
733 | =head3 Automatically creating related objects |
734 | |
735 | You might have a class C<Artist> which has many C<CD>s. Further, you |
736 | want to create a C<CD> object every time you insert an C<Artist> object. |
ccbebdbc |
737 | You can accomplish this by overriding C<insert> on your objects: |
086b93a2 |
738 | |
739 | sub insert { |
ccbebdbc |
740 | my ( $self, @args ) = @_; |
741 | $self->next::method(@args); |
086b93a2 |
742 | $self->cds->new({})->fill_from_artist($self)->insert; |
743 | return $self; |
744 | } |
745 | |
746 | where C<fill_from_artist> is a method you specify in C<CD> which sets |
747 | values in C<CD> based on the data in the C<Artist> object you pass in. |
748 | |
1def3451 |
749 | =head2 Debugging DBIx::Class objects with Data::Dumper |
750 | |
751 | L<Data::Dumper> can be a very useful tool for debugging, but sometimes it can |
752 | be hard to find the pertinent data in all the data it can generate. |
753 | Specifically, if one naively tries to use it like so, |
754 | |
755 | use Data::Dumper; |
756 | |
757 | my $cd = $schema->resultset('CD')->find(1); |
758 | print Dumper($cd); |
759 | |
760 | several pages worth of data from the CD object's schema and result source will |
761 | be dumped to the screen. Since usually one is only interested in a few column |
762 | values of the object, this is not very helpful. |
763 | |
764 | Luckily, it is possible to modify the data before L<Data::Dumper> outputs |
765 | it. Simply define a hook that L<Data::Dumper> will call on the object before |
766 | dumping it. For example, |
767 | |
768 | package My::DB::CD; |
769 | |
770 | sub _dumper_hook { |
99fb1058 |
771 | $_[0] = bless { |
772 | %{ $_[0] }, |
1def3451 |
773 | result_source => undef, |
99fb1058 |
774 | }, ref($_[0]); |
1def3451 |
775 | } |
776 | |
777 | [...] |
778 | |
779 | use Data::Dumper; |
780 | |
781 | $Data::Dumper::Freezer = '_dumper_hook'; |
782 | |
783 | my $cd = $schema->resultset('CD')->find(1); |
784 | print Dumper($cd); |
785 | # dumps $cd without its ResultSource |
786 | |
787 | If the structure of your schema is such that there is a common base class for |
788 | all your table classes, simply put a method similar to C<_dumper_hook> in the |
789 | base class and set C<$Data::Dumper::Freezer> to its name and L<Data::Dumper> |
790 | will automagically clean up your data before printing it. See |
791 | L<Data::Dumper/EXAMPLES> for more information. |
792 | |
1def3451 |
793 | =head2 Retrieving a row object's Schema |
794 | |
795 | It is possible to get a Schema object from a row object like so, |
796 | |
797 | my $schema = $cd->result_source->schema; |
798 | my $artist_rs = $schema->resultset('Artist'); |
799 | # for example |
800 | |
801 | This can be useful when you don't want to pass around a Schema object to every |
802 | method. |
803 | |
4c248161 |
804 | =head2 Profiling |
805 | |
806 | When you enable L<DBIx::Class::Storage::DBI>'s debugging it prints the SQL |
807 | executed as well as notifications of query completion and transaction |
808 | begin/commit. If you'd like to profile the SQL you can subclass the |
809 | L<DBIx::Class::Storage::Statistics> class and write your own profiling |
810 | mechanism: |
811 | |
812 | package My::Profiler; |
813 | use strict; |
814 | |
815 | use base 'DBIx::Class::Storage::Statistics'; |
816 | |
817 | use Time::HiRes qw(time); |
818 | |
819 | my $start; |
820 | |
821 | sub query_start { |
822 | my $self = shift(); |
823 | my $sql = shift(); |
824 | my $params = @_; |
825 | |
826 | print "Executing $sql: ".join(', ', @params)."\n"; |
827 | $start = time(); |
828 | } |
829 | |
830 | sub query_end { |
831 | my $self = shift(); |
832 | my $sql = shift(); |
833 | my @params = @_; |
834 | |
835 | printf("Execution took %0.4f seconds.\n", time() - $start); |
836 | $start = undef; |
837 | } |
838 | |
839 | 1; |
840 | |
841 | You can then install that class as the debugging object: |
842 | |
843 | __PACKAGE__->storage()->debugobj(new My::Profiler()); |
844 | __PACKAGE__->storage()->debug(1); |
845 | |
846 | A more complicated example might involve storing each execution of SQL in an |
847 | array: |
848 | |
849 | sub query_end { |
850 | my $self = shift(); |
851 | my $sql = shift(); |
852 | my @params = @_; |
853 | |
854 | my $elapsed = time() - $start; |
855 | push(@{ $calls{$sql} }, { |
856 | params => \@params, |
857 | elapsed => $elapsed |
858 | }); |
859 | } |
860 | |
861 | You could then create average, high and low execution times for an SQL |
862 | statement and dig down to see if certain parameters cause aberrant behavior. |
863 | |
e8e9e5c7 |
864 | =head2 Getting the value of the primary key for the last database insert |
865 | |
74413b83 |
866 | AKA getting last_insert_id |
867 | |
e8e9e5c7 |
868 | If you are using PK::Auto, this is straightforward: |
869 | |
74413b83 |
870 | my $foo = $rs->create(\%blah); |
e8e9e5c7 |
871 | # do more stuff |
872 | my $id = $foo->id; # foo->my_primary_key_field will also work. |
873 | |
874 | If you are not using autoincrementing primary keys, this will probably |
875 | not work, but then you already know the value of the last primary key anyway. |
876 | |
40dbc108 |
877 | =cut |