Use with SQLAlchemy

chide has a special Set subclass that helps to make sure only one sample object is created with a particular primary key in any one table.

For example, given these two models:

class Parent(Base):
    __tablename__ = 'parent'
    id = Column(Integer, primary_key=True)
    child_id = Column(Integer, ForeignKey(''))
    child = relationship('Child')

class Child(Base):
    __tablename__ = 'child'
    id = Column(Integer, primary_key=True)
    value = Column(Integer)

We can set up a collection of sample values as follows:

from chide import Collection

samples = Collection({
    Parent: {'id': 1, 'child': Child},
    Child: {'id': 3, 'value': 42}

Now we can quickly make sample objects and add them to a session:

>>> session = Session()
>>> session.add(samples.make(Parent))
>>> session.commit()

This gives us a parent and a child:

>>> session.query(Parent).one()
<Parent ...>
>>> _.child
<Child ...>

If we create multiple parent objects and don’t want to have to worry about clashing children being created by mistake, we can use a chide.sqlalchemy.Set to make sure that we only have one sample object with a given primary key at any time:

>>> from chide.sqlalchemy import Set
>>> current_samples = Set(samples)
>>> session = Session()
>>> session.add(current_samples.get(Parent, id=1))
>>> session.add(current_samples.get(Parent, id=2))
>>> session.commit()

This gives us two parents that both point to the same child:

>>> parent1 = session.query(Parent).filter_by(id=1).one()
>>> parent2 = session.query(Parent).filter_by(id=2).one()
>>> parent1.child is parent2.child

Of course, if we want different children, that’s easy too:

>>> session = Session()
>>> session.add(current_samples.get(Parent, id=3, child=Child(value=6)))
>>> session.add(current_samples.get(Parent, id=4, child=Child(value=7)))
>>> session.commit()

The children’s primary keys will be created by the database, but the values are as we need them:

>>> parent3 = session.query(Parent).filter_by(id=3).one()
>>> parent3.child.value
>>> parent4 = session.query(Parent).filter_by(id=4).one()
>>> parent4.child.value