Richard Gerd Kuesters | Pollux <[email protected]> wrote:
> hi all! > > i'm dealing with a little problem here. i have a parent table and its two > inheritances. there is a value that both children have and must be unique > along either types. is there a way to move this column to the parent and use > a constraint in the child? my implementation is postgres 9.4+ with psycopg2 > only. if this is single table inheritance then the constraint would most ideally be placed on the parent class. if you’re trying to make this “magic” such that you can semantically keep the unique constraints on the child classes, you’d need to build out a conditional approach within @declared_attr. IMO I think this is an idealized edge case that in the real world doesn’t matter much - just do what works (put the col / constraint on the base). the approach is described at http://docs.sqlalchemy.org/en/rel_0_9/orm/extensions/declarative/inheritance.html#resolving-column-conflicts. You’d need to make this work for both the column and the constraint. > as a simple example (i'm just creating this example to simplify things), this > works: > ____________ > class MyParent(Base): > > foo_id = Column(Integer, Sequence('foo_id_seq'), primary_key=True) > foo_name = Column(Unicode(64), nullable=False) > foo_type = Column(Integer, nullable=False) > > __mapper_args__ = { > "polymorphic_on": foo_type, > "polymorphic_identity": 0 > } > > > class MyChild1(MyParent): > > foo_id = Column(Integer, ForeignKey(MyParent.foo_id), primary_key=True) > bar_id = Column(Integer, ForeignKey(AnotherEntity.bar_id), nullable=False) > child1_specific_name = Column(Unicode(5), nullable=False) > child1_baz_stuff = Column(Boolean, default=False) > > __mapper_args__ = { > "polymorphic_identity": 1 > } > > __table_args__ = ( > UniqueConstraint(bar_id, child1_specific_name,), # works, bar_id is > in MyChild1 > ) > > > class MyChild2(MyParent): > > foo_id = Column(Integer, ForeignKey(MyParent.foo_id), primary_key=True) > bar_id = Column(Integer, ForeignKey(AnotherEntity.bar_id), nullable=False) > child2_specific_code = Column(UUID, nullable=False) > child2_baz_stuff = Column(Float, nullable=False) > > __mapper_args__ = { > "polymorphic_identity": 2 > } > > __table_args__ = ( > UniqueConstraint(bar_id, child2_specific_code,), # works, bar_id is > in MyChild2 > ) > ____________ > > but i would like to do this, if possible: > ____________ > class MyParent(Base): > > foo_id = Column(Integer, Sequence('foo_id_seq'), primary_key=True) > foo_name = Column(Unicode(64), nullable=False) > foo_type = Column(Integer, nullable=False) > bar_id = Column(Integer, ForeignKey(AnotherEntity.bar_id), > nullable=False) # since both child uses bar_id, why not having it on the > parent? > > __mapper_args__ = { > "polymorphic_on": foo_type, > "polymorphic_identity": 0 > } > > > class MyChild1(MyParent): > > foo_id = Column(Integer, ForeignKey(MyParent.foo_id), primary_key=True) > child1_specific_name = Column(Unicode(5), nullable=False) > child1_baz_stuff = Column(Boolean, default=False) > > __mapper_args__ = { > "polymorphic_identity": 1 > } > > __table_args__ = ( > UniqueConstraint(MyParent.bar_id, child1_specific_name,), # will it > work? > ) > > > class MyChild2(MyParent): > > foo_id = Column(Integer, ForeignKey(MyParent.foo_id), primary_key=True) > child2_specific_code = Column(UUID, nullable=False) > child2_baz_stuff = Column(Float, nullable=False) > > __mapper_args__ = { > "polymorphic_identity": 2 > } > > __table_args__ = ( > UniqueConstraint(MyParent.bar_id, child2_specific_code,), # will it > work? > ) > ____________ > > well, will it work without being a concrete inheritance? :) > > > best regards, > richard. > > > -- > You received this message because you are subscribed to the Google Groups > "sqlalchemy" group. > To unsubscribe from this group and stop receiving emails from it, send an > email to [email protected]. > To post to this group, send email to [email protected]. > Visit this group at http://groups.google.com/group/sqlalchemy. > For more options, visit https://groups.google.com/d/optout. -- You received this message because you are subscribed to the Google Groups "sqlalchemy" group. To unsubscribe from this group and stop receiving emails from it, send an email to [email protected]. To post to this group, send email to [email protected]. Visit this group at http://groups.google.com/group/sqlalchemy. For more options, visit https://groups.google.com/d/optout.
