mirror of
https://github.com/sqlalchemy/sqlalchemy.git
synced 2026-05-10 10:50:37 -04:00
Mike Bayer
47 lines
1.4 KiB
Python
47 lines
1.4 KiB
Python
"""
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Illustrates how to mix table reflection with Declarative, such that
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the reflection process itself can take place **after** all classes
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are defined. Declarative classes can also override column
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definitions loaded from the database.
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At the core of this example is the ability to change how Declarative
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assigns mappings to classes. The ``__mapper_cls__`` special attribute
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is overridden to provide a function that gathers mapping requirements
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as they are established, without actually creating the mapping.
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Then, a second class-level method ``prepare()`` is used to iterate
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through all mapping configurations collected, reflect the tables
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named within and generate the actual mappers.
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The example is new in 0.7.5 and makes usage of the new
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``autoload_replace`` flag on :class:`.Table` to allow declared
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classes to override reflected columns.
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Usage example::
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Base = declarative_base(cls=DeclarativeReflectedBase)
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class Foo(Base):
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__tablename__ = 'foo'
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bars = relationship("Bar")
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class Bar(Base):
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__tablename__ = 'bar'
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# illustrate overriding of "bar.foo_id" to have
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# a foreign key constraint otherwise not
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# reflected, such as when using MySQL
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foo_id = Column(Integer, ForeignKey('foo.id'))
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Base.prepare(e)
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s = Session(e)
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s.add_all([
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Foo(bars=[Bar(data='b1'), Bar(data='b2')], data='f1'),
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Foo(bars=[Bar(data='b3'), Bar(data='b4')], data='f2')
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])
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s.commit()
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"""
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