Class HasManyThrough

source code

 object --+        
          |        
Association --+    
              |    
            Has --+
                  |
                 HasManyThrough

The HasManyThrough class is used whenever a has_many association is created with the through option. It works by using the association id given with the through option as a proxy association to another class on which a source association is defined. The source class for a has many through association will be the source class of the source association. This means that the scope for a has many through association is actually two scopes chained together. The proxy scope is used to retrieve the records on which to build the source association, which is used to build a scope for the records represented by the has many through association. The proxy and source associations may be any of the simple has or belongs to association types.

Options specific to has many through associations

• through: the association id of an association defined on the target class. This association will be used as the proxy association, and it is an error if this association does not exist.
• source: the id of the source association. If the source option is not specified, we assume that the source association's id is the same as the has many through association's id.
• source_type: the name of the source class as a string. This option may be required if the source class is ambiguous, such as when the source association is a polymorphic belongs_to association.

Has many through example

This example shows how to create a basic has many through relationship in which the internet has many connected devices through its networks. The has many through association is defined on the Internet class. Notice how the proxy association, networks, is defined on the target class, Internet, and the source association, devices, is defined on the proxy association's source class, Network. Therefore, the source class for the entire relation is the source association's source class, Device:

   class Internet(pyperry.Base):
       def _config(cls):
           cls.attributes('id')
           cls.has_many('connected_devices', through='networks', source='devices')
           cls.has_many('networks', class_name='Network')

   class Network(pyperry.Base):
       def _config(cls):
           cls.attributes('id', 'internet_id')
           cls.belongs_to('internet', class_name='Internet')
           cls.has_many('devices', class_name='Device')

   class Device(pyperry.Base):
       def _config(cls):
           cls.attributes('id', 'network_id')
           cls.belongs_to('network', class_name='Network')

   has_many('widgets', klass=Widget, foreign_key='widget_id')
   has_many('comments', as_='parent')

   where('widget_id = %s ' % target['id'])

   where('parent_id = %s AND parent_type = %s' % (target['id'],
   target.class))