Provided by: librose-db-object-perl_0.815-1_all 
NAME
Rose::DB::Object::Metadata::Relationship::ManyToMany - Many to many table relationship
metadata object.
SYNOPSIS
use Rose::DB::Object::Metadata::Relationship::ManyToMany;
$rel = Rose::DB::Object::Metadata::Relationship::ManyToMany->new(...);
$rel->make_methods(...);
...
DESCRIPTION
Objects of this class store and manipulate metadata for relationships in which rows from
one table are connected to rows in another table through an intermediate table that maps
between them.
This class inherits from Rose::DB::Object::Metadata::Relationship. Inherited methods that
are not overridden will not be documented a second time here. See the
Rose::DB::Object::Metadata::Relationship documentation for more information.
EXAMPLE
Consider the following tables.
CREATE TABLE widgets
(
id SERIAL PRIMARY KEY,
name VARCHAR(255)
);
CREATE TABLE colors
(
id SERIAL PRIMARY KEY,
name VARCHAR(255)
);
CREATE TABLE widget_color_map
(
id SERIAL PRIMARY KEY,
widget_id INT NOT NULL REFERENCES widgets (id),
color_id INT NOT NULL REFERENCES colors (id),
UNIQUE(widget_id, color_id)
);
Given these tables, each widget can have zero or more colors, and each color can be
applied to zero or more widgets. This is the type of "many to many" relationship that
this class is designed to handle.
In order to do so, each of the three of the tables that participate in the relationship
must be fronted by its own Rose::DB::Object-derived class. Let's call those classes
"Widget", "Color", and "WidgetColorMap".
The class that maps between the other two classes is called the "map class." In this
example, it's "WidgetColorMap". The map class must have a foreign key and/or "many to
one" relationship pointing to each of the two classes that it maps between.
When it comes to actually creating the three classes that participate in a "many to many"
relationship, there's a bit of a "chicken and egg" problem. All these classes need to
know about each other more or less "simultaneously," but they must be defined in a serial
fashion, and may be loaded in any order by the user.
In order to account for this, method creation may be deferred for any foreign key or
relationship that does not yet have all the information it requires to do its job. This
should be transparent to the developer.
Here's a complete example using the "Widget", "Color", and "WidgetColorMap" classes.
First, the "Widget" class which has a "many to many" relationship through which it can
retrieve its colors.
package Widget;
use base 'Rose::DB::Object';
__PACKAGE__->meta->setup
(
table => 'widgets',
columns =>
[
id => { type => 'int', primary_key => 1 },
name => { type => 'varchar', length => 255 },
],
relationships =>
[
# Define "many to many" relationship to get colors
colors =>
{
type => 'many to many',
map_class => 'WidgetColorMap',
# These are only necessary if the relationship is ambiguous
#map_from => 'widget',
#map_to => 'color',
},
],
);
1;
Next, the "Color" class which has a "many to many" relationship through which it can
retrieve all the widgets that have this color.
package Color;
use base 'Rose::DB::Object';
__PACKAGE__->meta->setup
(
table => 'colors',
columns =>
[
id => { type => 'int', primary_key => 1 },
name => { type => 'varchar', length => 255 },
],
relationships =>
[
# Define "many to many" relationship to get widgets
widgets =>
{
type => 'many to many',
map_class => 'WidgetColorMap',
# These are only necessary if the relationship is ambiguous
#map_from => 'color',
#map_to => 'widget',
},
],
);
1;
Finally, the "WidgetColorMap" class must have a foreign key or "many to one" relationship
for each of the two classes that it maps between ("Widget" and "Color").
package WidgetColorMap;
use base 'Rose::DB::Object';
__PACKAGE__->meta->setup
(
table => 'widget_color_map',
columns =>
[
id => { type => 'int', primary_key => 1 },
widget_id => { type => 'int' },
color_id => { type => 'int' },
],
foreign_keys =>
[
# Define foreign keys that point to each of the two classes
# that this class maps between.
color =>
{
class => 'Color',
key_columns => { color_id => 'id' },
},
widget =>
{
class => 'Widget',
key_columns => { widget_id => 'id' },
},
],
);
1;
Here's an initial set of data and some examples of the above classes in action. First,
the data:
INSERT INTO widgets (id, name) VALUES (1, 'Sprocket');
INSERT INTO widgets (id, name) VALUES (2, 'Flange');
INSERT INTO colors (id, name) VALUES (1, 'Red');
INSERT INTO colors (id, name) VALUES (2, 'Green');
INSERT INTO colors (id, name) VALUES (3, 'Blue');
INSERT INTO widget_color_map (widget_id, color_id) VALUES (1, 1);
INSERT INTO widget_color_map (widget_id, color_id) VALUES (1, 2);
INSERT INTO widget_color_map (widget_id, color_id) VALUES (2, 3);
Now the code:
use Widget;
use Color;
$widget = Widget->new(id => 1);
$widget->load;
@colors = map { $_->name } $widget->colors; # ('Red', 'Green')
$color = Color->new(id => 1);
$color->load;
@widgets = map { $_->name } $color->widgets; # ('Sprocket')
METHOD MAP
"count"
Rose::DB::Object::MakeMethods::Generic, objects_by_map, "interface => 'count'" ...
"find"
Rose::DB::Object::MakeMethods::Generic, objects_by_map, "interface => 'find'" ...
"iterator"
Rose::DB::Object::MakeMethods::Generic, objects_by_map, "interface => 'iterator'" ...
"get_set"
Rose::DB::Object::MakeMethods::Generic, objects_by_map, "interface => 'get_set'" ...
"get_set_now"
Rose::DB::Object::MakeMethods::Generic, objects_by_map, "interface => 'get_set_now'"
...
"get_set_on_save"
Rose::DB::Object::MakeMethods::Generic, objects_by_map, "interface =>
'get_set_on_save'" ...
"add_now"
Rose::DB::Object::MakeMethods::Generic, objects_by_map, "interface => 'add_now'" ...
"add_on_save"
Rose::DB::Object::MakeMethods::Generic, objects_by_map, "interface => 'add_on_save'"
...
See the Rose::DB::Object::Metadata::Relationship documentation for an explanation of this
method map.
CLASS METHODS
default_auto_method_types [TYPES]
Get or set the default list of auto_method_types. TYPES should be a list of
relationship method types. Returns the list of default relationship method types (in
list context) or a reference to an array of the default relationship method types (in
scalar context). The default list contains "get_set_on_save" and "add_on_save".
OBJECT METHODS
build_method_name_for_type TYPE
Return a method name for the relationship method type TYPE.
For the method types "get_set", "get_set_now", and "get_set_on_save", the
relationship's name is returned.
For the method types "add_now" and "add_on_save", the relationship's name prefixed
with "add_" is returned.
For the method type "find", the relationship's name prefixed with "find_" is returned.
For the method type "count", the relationship's name suffixed with "_count" is
returned.
For the method type "iterator", the relationship's name suffixed with "_iterator" is
returned.
Otherwise, undef is returned.
is_singular
Returns false.
manager_class [CLASS]
Get or set the name of the Rose::DB::Object::Manager-derived class that the map_class
will use to fetch records. The make_methods method will use Rose::DB::Object::Manager
if this value is left undefined.
manager_method [METHOD]
Get or set the name of the manager_class class method to call when fetching records.
The make_methods method will use get_objects if this value is left undefined.
manager_count_method [METHOD]
Get or set the name of the manager_class class method to call when counting objects.
The make_methods method will use get_objects_count if this value is left undefined.
manager_iterator_method [METHOD]
Get or set the name of the manager_class class method to call when creating an
iterator. The make_methods method will use get_objects_iterator if this value is left
undefined.
manager_args [HASHREF]
Get or set a reference to a hash of name/value arguments to pass to the manager_method
when fetching objects. For example, this can be used to enforce a particular sort
order for objects fetched via this relationship. Modifying the example above:
Widget->meta->add_relationship
(
colors =>
{
type => 'many to many',
map_class => 'WidgetColorMap',
manager_args => { sort_by => Color->meta->table . '.name' },
},
);
This would ensure that a "Widget"'s "colors()" are listed in alphabetical order. Note
that the "name" column is prefixed by the name of the table fronted by the "Color"
class. This is important because several tables may have a column named "name." If
this relationship is used to form a JOIN in a query along with one of those tables,
then the "name" column will be ambiguous. Adding a table name prefix disambiguates
the column name.
Also note that the table name is not hard-coded. Instead, it is fetched from the
Rose::DB::Object-derived class that fronts the table. This is more verbose, but is a
much better choice than including the literal table name when it comes to long-term
maintenance of the code.
See the documentation for Rose::DB::Object::Manager's get_objects method for a full
list of valid arguments for use with the "manager_args" parameter, but remember that
you can define your own custom manager_class and thus can also define what kinds of
arguments "manager_args" will accept.
Note: when the name of a relationship that has "manager_args" is used in a
Rose::DB::Object::Manager with_objects or require_objects parameter value, only the
sort_by argument will be copied from "manager_args" and incorporated into the query.
map_class [CLASS]
Get or set the name of the Rose::DB::Object-derived class that fronts the table that
maps between the other two tables. This class must have a foreign key and/or "many to
one" relationship for each of the two tables that it maps between.
In the example above, the map class is "WidgetColorMap".
map_from [NAME]
Get or set the name of the "many to one" relationship or foreign key in map_class that
points to the object of the current class. Setting this value is only necessary if
the map class has more than one foreign key or "many to one" relationship that points
to one of the classes that it maps between.
In the example above, the value of map_from would be "widget" when defining the "many
to many" relationship in the "Widget" class, or "color" when defining the "many to
many" relationship in the "Color" class. Neither of these settings is necessary in
the example because the "WidgetColorMap" class has one foreign key that points to each
class, so there is no ambiguity.
map_to [NAME]
Get or set the name of the "many to one" relationship or foreign key in map_class that
points to the "foreign" object to be fetched. Setting this value is only necessary if
the map class has more than one foreign key or "many to one" relationship that points
to one of the classes that it maps between.
In the example above, the value of map_from would be "color" when defining the "many
to many" relationship in the "Widget" class, or "widget" when defining the "many to
many" relationship in the "Color" class. Neither of these settings is necessary in
the example because the "WidgetColorMap" class has one foreign key that points to each
class, so there is no ambiguity.
query_args [ARRAYREF]
Get or set a reference to an array of query arguments to add to the query passed to
the manager_method when fetching objects.
This can be used to limit the objects fetched via this relationship. For example,
modifying the example above:
Widget->meta->add_relationship
(
colors =>
{
type => 'many to many',
map_class => 'WidgetColorMap',
query_args => [ name => { like => '%e%' } ],
},
);
See the documentation for Rose::DB::Object::Manager's get_objects method for a full
list of valid "query" arguments.
share_db [BOOL]
Get or set a boolean flag that indicates whether or not all of the classes involved in
fetching objects via this relationship (including the objects themselves) will share
the same Rose::DB-derived db object. Defaults to true.
type
Returns "many to many".
AUTHOR
John C. Siracusa (siracusa@gmail.com)
LICENSE
Copyright (c) 2010 by John C. Siracusa. All rights reserved. This program is free
software; you can redistribute it and/or modify it under the same terms as Perl itself.
perl v5.20.2 Rose::DB::Object::Metadata::Relationship::ManyToMany(3pm)