4.5.8 Fetching and inheritance

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4.5.8 Fetching and inheritance

(TBD: This section has to be rewritten - for the moment being it consists mostly of a copy-paste of messages exchanged on the mailing-list)

Suppose you have the following model:

  Address <<-toAddresses---toEmployee-> Employee
                                           ^
                                          / \
                                           T
                                           |
                                   +--------------+
                                   |              |
                               Executive      SalesClerk

(See the full model description in section 2.1.2)

An address object can be transparently linked to either an Employee, an Executive or a SalesClerk instance. There is nothing particular to do, this is automatically handled.
address.toEmployee() will automatically retrieve the right object (being an instance of one of those three classes). Here again, no particular action is needed, the framework handles it for you.

Now, when fetching, you can specify whether you want to fetch a single class or its inheritance tree as well. Compare this, based on the test database and model StoreEmployees:

  >>> from StoreEmployees import Address
  >>> from Modeling.EditingContext import EditingContext as EC
  >>> ec = EC()
  >>> qualifier='toAddresses.zipCode like "4*"'
  >>> ec.fetch('Employee', qualifier)
  []
  >>> # Now fetch against the inheritance tree below 'Employee'
  ... all_objects=ec.fetch('Employee', qualifier, isDeep=1)
  >>> [(o.entityName(), o.getFirstName(),o.getLastName())
  ...  for o in all_objects]
  [('SalesClerk', 'John Jr.', 'Cleese'), 
   ('SalesClerk', 'Jeanne', 'Cleese'), 
   ('Executive', 'John', 'Cleese')]

As you can see, specifying isDeep=1 when fetching allows you to fetch against the whole inheritance tree for a given entity (here, Employee).

Comments are welcome: Sebastien Bigaret / Modeling Home Page
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