Modeling: User's Guide

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3.1.2.2 Dynamic generation using metaclass

The second method makes use of the metaclass dynamic.CustomObjectMeta:

# file: Book.py
# We assume that the model is already loaded
from Modeling import dynamic

class Book:
  __metaclass__=dynamic.CustomObjectMeta
  entityName='Book'
  mdl_define_properties=1

  # your own code here

The metaclass CustomObjectMeta automatically adds all the necessary methods to a class for integration with the modeling framework. It looks for the following attributes in the class:

• entityNamed`: mandatory, this is the name of the class' entity. The corresponding model should have been loaded prior to the class declaration, or you'll get a dynamic.EntityNotFound exception.

• verbose_metaclass: if set, the metaclass prints on sys.stderr some info while building the class.

• mdl_define_properties: if set, the metaclass will also add properties for each attribute on relationship in the entity.

Last, then dynamic module also offers a method build_with_metaclass(model, define_properties=0, verbose=0) which you can use to derive the necessary package and modules from a model just like dynamic.build() we saw above, the ony difference being that the classes created at runtime use the metaclass approach.

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Modeling: User's Guide

Previous: 3.1.2.1 Dynamic generating of Up: 3.1.2 Building the python Next: 3.1.3 Static vs. dynamic:

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Release 0.9, documentation updated on March 4, 2006.

Comments are welcome: Sebastien Bigaret / Modeling Home Page
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