SQLAlchemy - order_by on relationship for join table

问题

I'm using declarative SQLAlchemy and I have three models: Role, Permission, and RolePermission. In my Role model, I have the following:

class Role(Base):
    name = Column(u'NAME', VARCHAR(50), nullable=False, unique=True)
    permissionLinks = relationship(RolePermission, backref="role", order_by=name)
    permissions = relationship(Permission, backref=backref("roles",
      order_by=name), secondary=RolePermission.__table__,
      order_by=Permission.name)

Now the permissions declaration works fine, and the permissions associated with a role come out sorted as I expect (by name). However, permissionLinks fails with the following error:

sqlalchemy.exc.ProgrammingError: (ProgrammingError) ('42000', '[42000] [Microsoft][ODBC SQL Server Driver][SQL Server]The multi-part identifier "ROLES.NAME" could not be bound. (4104) (SQLExecDirectW); [42000] [Microsoft][ODBC SQL Server Driver][SQL Server]Statement(s) could not be prepared. (8180)') u'SELECT [ROLES_PERMISSIONS].[ROLE_ID] AS [ROLES_PERMISSIONS_ROLE_ID], [ROLES_PERMISSIONS].[PERMISSION_ID] AS [ROLES_PERMISSIONS_PERMISSION_ID], [ROLES_PERMISSIONS].[IS_DENIED] AS [ROLES_PERMISSIONS_IS_DENIED] \nFROM [ROLES_PERMISSIONS] \nWHERE [ROLES_PERMISSIONS].[ROLE_ID] = ? ORDER BY [ROLES].[NAME]' (19,)

The problem is that Role is not being joined, so it can't sort by Role.name. I tried specifying primaryjoin=id == RolePermission.id1, but that didn't seem to change anything. How can I specify a join on this relationship such that I can sort by a field in one of the joined tables (namely, Role.name)?

回答1:

I couldn't make any of these solutions work, however I found an easier way.

from sqlalchemy.ext.declarative import declarative_base

class User(Base):
    # ....
    addresses = relationship("Address",
                         order_by="desc(Address.email)",
                         primaryjoin="Address.user_id==User.id")

Found here: http://docs.sqlalchemy.org/en/latest/orm/extensions/declarative/relationships.html

回答2:

What you want is to order the role attribute of the RolePermission object. Passing order_by sets the order in the Role class.

Try this:

from sqlalchemy.orm import backref

permissionLinks = relationship(RolePermission, backref=backref("role", order_by=name))

setting an order for the back reference

回答3:

The problem is in permissionLinks relationship. Ordering its items by by Role.name makes no sense to me.

来源：https://stackoverflow.com/questions/6750251/sqlalchemy-order-by-on-relationship-for-join-table

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python

sql

model

sqlalchemy

declarative