I have a set of tables that look like:
workflows = Table('workflows', Base.metadata,
Column('id', Integer, primary_key=True),
)
actions = Table('actions', Base.metadata,
Column('name', String, primary_key=True),
Column('workflow_id', Integer, ForeignKey(workflows.c.id), primary_key=True),
)
action_dependencies = Table('action_dependencies', Base.metadata,
Column('workflow_id', Integer, ForeignKey(workflows.c.id), primary_key=True),
Column('parent_action', String, ForeignKey(actions.c.name), primary_key=True),
Column('child_action', String, ForeignKey(actions.c.name), primary_key=True),
)
My ORM classes look like:
class Workflow(Base):
__table__ = workflows
actions = relationship("Action", order_by="Action.name", backref="workflow")
class Action(Base):
__table__ = actions
children = relationship("Action",
secondary=action_dependencies,
primaryjoin=actions.c.name == action_dependencies.c.parent_action,
secondaryjoin=actions.c.name == action_dependencies.c.child_action,
backref="parents"
)
So in my system, each action is uniquely identified by a combination of a workflow id and its name. I'd like each action to have parents
and children
attribute that refers its parent and child actions. Each action can have multiple parents and children.
The problem occurs when I have a function such as :
def set_parents(session, workflow_id, action_name, parents):
action = session.query(db.Action).filter(db.Action.workflow_id == workflow.id).filter(db.Action.name == action_name).one()
for parent_name in parents:
parent = session.query(db.Action).filter(db.Action.workflow_id == workflow.id).filter(db.Action.name == parent_name).one()
action.parents.append(parent)
session.commit()
I get an error like:
IntegrityError: (IntegrityError) action_dependencies.workflow_id may not be NULL u'INSERT INTO action_dependencies (parent_action, child_action) VALUES (?, ?)' (u'directory_creator', u'packing')
How do I get the relationship to set the workflow_id correctly?
See below working code. The key points are those I mentioned in the comments:
ForeignKey
s relationship
configuration using the FKs Code:
workflows = Table('workflows', Base.metadata,
Column('id', Integer, primary_key=True),
)
actions = Table('actions', Base.metadata,
Column('workflow_id', Integer, ForeignKey(workflows.c.id), primary_key=True),
Column('name', String, primary_key=True),
)
action_dependencies = Table('action_dependencies', Base.metadata,
Column('workflow_id', Integer, ForeignKey(workflows.c.id), primary_key=True),
Column('parent_action', String, ForeignKey(actions.c.name), primary_key=True),
Column('child_action', String, ForeignKey(actions.c.name), primary_key=True),
ForeignKeyConstraint(['workflow_id', 'parent_action'], ['actions.workflow_id', 'actions.name']),
ForeignKeyConstraint(['workflow_id', 'child_action'], ['actions.workflow_id', 'actions.name']),
)
class Workflow(Base):
__table__ = workflows
actions = relationship("Action", order_by="Action.name", backref="workflow")
class Action(Base):
__table__ = actions
children = relationship("Action",
secondary=action_dependencies,
primaryjoin=and_(actions.c.name == action_dependencies.c.parent_action,
actions.c.workflow_id == action_dependencies.c.workflow_id),
secondaryjoin=and_(actions.c.name == action_dependencies.c.child_action,
actions.c.workflow_id == action_dependencies.c.workflow_id),
backref="parents"
)
# create db schema
Base.metadata.create_all(engine)
# create entities
w_1 = Workflow()
w_2 = Workflow()
a_11 = Action(name="ac-11", workflow=w_1)
a_12 = Action(name="ac-12", workflow=w_1)
a_21 = Action(name="ac-21", workflow=w_2)
a_22 = Action(name="ac-22", workflow=w_2)
session.add(w_1)
session.add(w_2)
a_22.parents.append(a_21)
session.commit()
session.expunge_all()
print '-'*80
# helper functions
def get_workflow(id):
return session.query(Workflow).get(id)
def get_action(name):
return session.query(Action).filter_by(name=name).one()
# test another OK
a_11 = get_action("ac-11")
a_12 = get_action("ac-12")
a_11.children.append(a_12)
session.commit()
session.expunge_all()
print '-'*80
# test KO (THIS SHOULD FAIL VIOLATING FK-constraint)
a_11 = get_action("ac-11")
a_22 = get_action("ac-22")
a_11.children.append(a_22)
session.commit()
session.expunge_all()
print '-'*80
I don't think it's correct to have the primary key a foreign key. How does that work?
But to make composite constraint, a key that is "unique together", use this in the table definition:
UniqueConstraint(u"name", u"workflow_id"),
But if you really want it to be the primary key also you can use this:
PrimaryKeyConstraint(*columns, **kw)
http://docs.sqlalchemy.org/en/latest/core/schema.html#sqlalchemy.schema.PrimaryKeyConstraint
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