SQLAlchemy：具有復合主鍵的關系表

Question

我有一組看起來像這樣的表：

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),
                           )

我的ORM類看起來像：

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"
                           )

因此，在我的系統中，每個操作都由工作流ID和名稱的組合唯一標識。 我希望每個動作都有parents和children屬性，指的是父母和孩子的行為。 每個動作都可以有多個父母和孩子。

當我有一個如下功能時，會出現問題：

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()

我得到一個錯誤：

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')

如何獲得正確設置workflow_id的關系？

Answer 1

見下面的工作代碼。 關鍵點是我在評論中提到的那些：

• 合適的復合ForeignKey
• 使用FK正確relationship配置

碼：

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

Answer 2

我認為將主鍵設為外鍵是不正確的。 這是如何運作的？

但是要創建復合約束，一個“一起唯一”的鍵，請在表定義中使用它：

UniqueConstraint(u"name", u"workflow_id"),

但如果你真的希望它成為主鍵，你也可以使用它：

PrimaryKeyConstraint(*columns, **kw)

http://docs.sqlalchemy.org/en/latest/core/schema.html#sqlalchemy.schema.PrimaryKeyConstraint