1Rose::DB::Object::MetadUasRteoars:e:C:Ro:enDltBar:ti:ibOoubntjseehdcitpP::e::rMMleatnDayodTcaoutMmaae:nn:ytR(ae3tl)iaotnionship::ManyToMany(3)
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NAME

6       Rose::DB::Object::Metadata::Relationship::ManyToMany - Many to many
7       table relationship metadata object.
8

SYNOPSIS

10         use Rose::DB::Object::Metadata::Relationship::ManyToMany;
11
12         $rel = Rose::DB::Object::Metadata::Relationship::ManyToMany->new(...);
13         $rel->make_methods(...);
14         ...
15

DESCRIPTION

17       Objects of this class store and manipulate metadata for relationships
18       in which rows from one table are connected to rows in another table
19       through an intermediate table that maps between them.
20
21       This class inherits from Rose::DB::Object::Metadata::Relationship.
22       Inherited methods that are not overridden will not be documented a
23       second time here.  See the Rose::DB::Object::Metadata::Relationship
24       documentation for more information.
25

EXAMPLE

27       Consider the following tables.
28
29           CREATE TABLE widgets
30           (
31             id    SERIAL PRIMARY KEY,
32             name  VARCHAR(255)
33           );
34
35           CREATE TABLE colors
36           (
37             id    SERIAL PRIMARY KEY,
38             name  VARCHAR(255)
39           );
40
41           CREATE TABLE widget_color_map
42           (
43             id         SERIAL PRIMARY KEY,
44             widget_id  INT NOT NULL REFERENCES widgets (id),
45             color_id   INT NOT NULL REFERENCES colors (id),
46             UNIQUE(widget_id, color_id)
47           );
48
49       Given these tables, each widget can have zero or more colors, and each
50       color can be applied to zero or more widgets.  This is the type of
51       "many to many" relationship that this class is designed to handle.
52
53       In order to do so, each of the three of the tables that participate in
54       the relationship must be fronted by its own Rose::DB::Object-derived
55       class.  Let's call those classes "Widget", "Color", and
56       "WidgetColorMap".
57
58       The class that maps between the other two classes is called the "map
59       class."  In this example, it's "WidgetColorMap".  The map class must
60       have a foreign key and/or "many to one" relationship pointing to each
61       of the two classes that it maps between.
62
63       When it comes to actually creating the three classes that participate
64       in a "many to many" relationship, there's a bit of a "chicken and egg"
65       problem.  All these classes need to know about each other more or less
66       "simultaneously," but they must be defined in a serial fashion, and may
67       be loaded in any order by the user.
68
69       In order to account for this, method creation may be deferred for any
70       foreign key or relationship that does not yet have all the information
71       it requires to do its job.  This should be transparent to the
72       developer.
73
74       Here's a complete example using the "Widget", "Color", and
75       "WidgetColorMap" classes.  First, the "Widget" class which has a "many
76       to many" relationship through which it can retrieve its colors.
77
78         package Widget;
79
80         use base 'Rose::DB::Object';
81
82         __PACKAGE__->meta->setup
83         (
84           table => 'widgets',
85
86           columns =>
87           [
88             id   => { type => 'int', primary_key => 1 },
89             name => { type => 'varchar', length => 255 },
90           ],
91
92           relationships =>
93           [
94             # Define "many to many" relationship to get colors
95             colors =>
96             {
97               type      => 'many to many',
98               map_class => 'WidgetColorMap',
99
100               # These are only necessary if the relationship is ambiguous
101               #map_from  => 'widget',
102               #map_to    => 'color',
103             },
104           ],
105         );
106
107         1;
108
109       Next, the "Color" class which has a "many to many" relationship through
110       which it can retrieve all the widgets that have this color.
111
112         package Color;
113
114         use base 'Rose::DB::Object';
115
116         __PACKAGE__->meta->setup
117         (
118           table => 'colors',
119
120           columns =>
121           [
122             id   => { type => 'int', primary_key => 1 },
123             name => { type => 'varchar', length => 255 },
124           ],
125
126           relationships =>
127           [
128             # Define "many to many" relationship to get widgets
129             widgets =>
130             {
131               type      => 'many to many',
132               map_class => 'WidgetColorMap',
133
134               # These are only necessary if the relationship is ambiguous
135               #map_from  => 'color',
136               #map_to    => 'widget',
137             },
138           ],
139         );
140
141         1;
142
143       Finally, the "WidgetColorMap" class must have a foreign key or "many to
144       one" relationship for each of the two classes that it maps between
145       ("Widget" and "Color").
146
147         package WidgetColorMap;
148
149         use base 'Rose::DB::Object';
150
151         __PACKAGE__->meta->setup
152         (
153           table => 'widget_color_map',
154
155           columns =>
156           [
157             id        => { type => 'int', primary_key => 1 },
158             widget_id => { type => 'int' },
159             color_id  => { type => 'int' },
160           ],
161
162           foreign_keys =>
163           [
164             # Define foreign keys that point to each of the two classes
165             # that this class maps between.
166             color =>
167             {
168               class => 'Color',
169               key_columns => { color_id => 'id' },
170             },
171
172             widget =>
173             {
174               class => 'Widget',
175               key_columns => { widget_id => 'id' },
176             },
177           ],
178         );
179
180         1;
181
182       Here's an initial set of data and some examples of the above classes in
183       action.  First, the data:
184
185         INSERT INTO widgets (id, name) VALUES (1, 'Sprocket');
186         INSERT INTO widgets (id, name) VALUES (2, 'Flange');
187
188         INSERT INTO colors (id, name) VALUES (1, 'Red');
189         INSERT INTO colors (id, name) VALUES (2, 'Green');
190         INSERT INTO colors (id, name) VALUES (3, 'Blue');
191
192         INSERT INTO widget_color_map (widget_id, color_id) VALUES (1, 1);
193         INSERT INTO widget_color_map (widget_id, color_id) VALUES (1, 2);
194         INSERT INTO widget_color_map (widget_id, color_id) VALUES (2, 3);
195
196       Now the code:
197
198         use Widget;
199         use Color;
200
201         $widget = Widget->new(id => 1);
202         $widget->load;
203
204         @colors = map { $_->name } $widget->colors; # ('Red', 'Green')
205
206         $color = Color->new(id => 1);
207         $color->load;
208
209         @widgets = map { $_->name } $color->widgets; # ('Sprocket')
210

METHOD MAP

212       "count"
213           Rose::DB::Object::MakeMethods::Generic, objects_by_map, "interface
214           => 'count'" ...
215
216       "find"
217           Rose::DB::Object::MakeMethods::Generic, objects_by_map, "interface
218           => 'find'" ...
219
220       "iterator"
221           Rose::DB::Object::MakeMethods::Generic, objects_by_map, "interface
222           => 'iterator'" ...
223
224       "get_set"
225           Rose::DB::Object::MakeMethods::Generic, objects_by_map, "interface
226           => 'get_set'" ...
227
228       "get_set_now"
229           Rose::DB::Object::MakeMethods::Generic, objects_by_map, "interface
230           => 'get_set_now'" ...
231
232       "get_set_on_save"
233           Rose::DB::Object::MakeMethods::Generic, objects_by_map, "interface
234           => 'get_set_on_save'" ...
235
236       "add_now"
237           Rose::DB::Object::MakeMethods::Generic, objects_by_map, "interface
238           => 'add_now'" ...
239
240       "add_on_save"
241           Rose::DB::Object::MakeMethods::Generic, objects_by_map, "interface
242           => 'add_on_save'" ...
243
244       See the Rose::DB::Object::Metadata::Relationship documentation for an
245       explanation of this method map.
246

CLASS METHODS

248       default_auto_method_types [TYPES]
249           Get or set the default list of auto_method_types.   TYPES should be
250           a list of relationship method types.  Returns the list of default
251           relationship method types (in list context) or a reference to an
252           array of the default relationship method types (in scalar context).
253           The default list contains  "get_set_on_save" and "add_on_save".
254

OBJECT METHODS

256       build_method_name_for_type TYPE
257           Return a method name for the relationship method type TYPE.
258
259           For the method types "get_set", "get_set_now", and
260           "get_set_on_save", the relationship's name is returned.
261
262           For the method types "add_now" and "add_on_save", the
263           relationship's  name prefixed with "add_" is returned.
264
265           For the method type "find", the relationship's name prefixed with
266           "find_" is returned.
267
268           For the method type "count", the relationship's name suffixed with
269           "_count" is returned.
270
271           For the method type "iterator", the relationship's name suffixed
272           with "_iterator" is returned.
273
274           Otherwise, undef is returned.
275
276       is_singular
277           Returns false.
278
279       manager_class [CLASS]
280           Get or set the name of the Rose::DB::Object::Manager-derived class
281           that the map_class will use to fetch records.  The make_methods
282           method will use Rose::DB::Object::Manager if this value is left
283           undefined.
284
285       manager_method [METHOD]
286           Get or set the name of the manager_class class method to call when
287           fetching records.  The make_methods method will use get_objects if
288           this value is left undefined.
289
290       manager_count_method [METHOD]
291           Get or set the name of the manager_class class method to call when
292           counting objects.  The make_methods method will use
293           get_objects_count if this value is left undefined.
294
295       manager_iterator_method [METHOD]
296           Get or set the name of the manager_class class method to call when
297           creating an iterator.  The make_methods method will use
298           get_objects_iterator if this value is left undefined.
299
300       manager_args [HASHREF]
301           Get or set a reference to a hash of name/value arguments to pass to
302           the manager_method when fetching objects.  For example, this can be
303           used to enforce a particular sort order for objects fetched via
304           this relationship.  Modifying the example above:
305
306             Widget->meta->add_relationship
307             (
308               colors =>
309               {
310                 type         => 'many to many',
311                 map_class    => 'WidgetColorMap',
312                 manager_args => { sort_by => Color->meta->table . '.name' },
313               },
314             );
315
316           This would ensure that a "Widget"'s "colors()" are listed in
317           alphabetical order.  Note that the "name" column is prefixed by the
318           name of the table fronted by the "Color" class.  This is important
319           because several tables may have a column named "name."  If this
320           relationship is used to form a JOIN in a query along with one of
321           those tables, then the "name" column will be ambiguous.  Adding a
322           table name prefix disambiguates the column name.
323
324           Also note that the table name is not hard-coded.  Instead, it is
325           fetched from the Rose::DB::Object-derived class that fronts the
326           table.  This is more verbose, but is a much better choice than
327           including the literal table name when it comes to long-term
328           maintenance of the code.
329
330           See the documentation for Rose::DB::Object::Manager's get_objects
331           method for a full list of valid arguments for use with the
332           "manager_args" parameter, but remember that you can define your own
333           custom manager_class and thus can also define what kinds of
334           arguments "manager_args" will accept.
335
336           Note: when the name of a relationship that has "manager_args" is
337           used in a Rose::DB::Object::Manager with_objects or require_objects
338           parameter value, only the sort_by argument will be copied from
339           "manager_args" and incorporated into the query.
340
341       map_class [CLASS]
342           Get or set the name of the Rose::DB::Object-derived class that
343           fronts the table that maps between the other two tables.  This
344           class must have a foreign key and/or "many to one" relationship for
345           each of the two tables that it maps between.
346
347           In the example above, the map class is "WidgetColorMap".
348
349       map_from [NAME]
350           Get or set the name of the "many to one" relationship or foreign
351           key in map_class that points to the object of the current class.
352           Setting this value is only necessary if the map class has more than
353           one foreign key or "many to one" relationship that points to one of
354           the classes that it maps between.
355
356           In the example above, the value of map_from would be "widget" when
357           defining the "many to many" relationship in the "Widget" class, or
358           "color" when defining the "many to many" relationship in the
359           "Color" class.  Neither of these settings is necessary in the
360           example because the "WidgetColorMap" class has one foreign key that
361           points to each class, so there is no ambiguity.
362
363       map_to [NAME]
364           Get or set the name of the "many to one" relationship or foreign
365           key in map_class that points to the "foreign" object to be fetched.
366           Setting this value is only necessary if the map class has more than
367           one foreign key or "many to one" relationship that points to one of
368           the classes that it maps between.
369
370           In the example above, the value of map_from would be "color" when
371           defining the "many to many" relationship in the "Widget" class, or
372           "widget" when defining the "many to many" relationship in the
373           "Color" class.  Neither of these settings is necessary in the
374           example because the "WidgetColorMap" class has one foreign key that
375           points to each class, so there is no ambiguity.
376
377       query_args [ARRAYREF]
378           Get or set a reference to an array of query arguments to add to the
379           query passed to the manager_method when fetching objects.
380
381           This can be used to limit the objects fetched via this
382           relationship.  For example, modifying the example above:
383
384             Widget->meta->add_relationship
385             (
386               colors =>
387               {
388                 type       => 'many to many',
389                 map_class  => 'WidgetColorMap',
390                 query_args => [ name => { like => '%e%' } ],
391               },
392             );
393
394           See the documentation for Rose::DB::Object::Manager's get_objects
395           method for a full list of valid "query" arguments.
396
397       share_db [BOOL]
398           Get or set a boolean flag that indicates whether or not all of the
399           classes involved in fetching objects via this relationship
400           (including the objects themselves) will share the same
401           Rose::DB-derived db object.  Defaults to true.
402
403       type
404           Returns "many to many".
405

AUTHOR

407       John C. Siracusa (siracusa@gmail.com)
408

LICENSE

410       Copyright (c) 2010 by John C. Siracusa.  All rights reserved.  This
411       program is free software; you can redistribute it and/or modify it
412       under the same terms as Perl itself.
413
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416perl v5.30.0           Rose::DB::O2b0j1e9c-t0:7:-M2e6tadata::Relationship::ManyToMany(3)
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