SQLAlchemy: mesa de Relación con primario compuesto clave

Question

Tengo un conjunto de tablas que se parecen:

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), 
          ) 

Mis clases ORM aspecto:

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" 
          ) 

Así que en mi sistema, cada acción es únicamente identificado por una combinación de una identificación de flujo de trabajo y su nombre. Me gustaría que cada acción tenga el atributo parents y children que refiere sus acciones principales y secundarias. Cada acción puede tener múltiples padres e hijos.

El problema se produce cuando tengo una función como:

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() 

me sale un error como:

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') 

¿Cómo consigo la relación a establecer el workflow_id correctamente?

Answer 1

Véase a continuación el código de trabajo. Los puntos clave son los que he mencionado en los comentarios:

• adecuada compuesta ForeignKey s configuración
• correcta relationship utilizando los FKs

Código:

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

No creo que sea correcto tener la clave principal como clave foránea. ¿Cómo funciona?

Pero para hacer limitación compuesto, una clave que es "único en conjunto", utilice esto en la definición de tabla:

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

Pero si realmente quiere que sea la clave principal también se puede utilizar esta:

PrimaryKeyConstraint(*columns, **kw) 

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