How to use relationships declared in the model.py ?

[andrew b]

So I see how you can access the columns in one of your model objects. For example ObjectQuery.user_name to get the user_name attribute from that query object. But how do I use the relationships that I setup in my model classes? I made a class definition where I join two tables(and it worked fine, but seems wasteful if there's a better way), because I couldn't figure out how to access the relation from the table below. 

Example code of mine:

class Role(DeclarativeBase):

    __tablename__ = 'roles'

    __table_args__ = {}

    #column definitions

    role_name = Column(u'role_name', VARCHAR(length=45))

    roles_id = Column(u'roles_id', INTEGER(), primary_key=True, nullable=False)

    #relation definitions

    projects = relation('Project', primaryjoin='Role.roles_id==ProjectRole.role_id', secondary=project_roles, secondaryjoin='ProjectRole.project_id==Project.projects_id')

[Christoph Zwerschke]

Am 13.02.2013 21:26, schrieb andrew b:
> So I see how you can access the columns in one of your model objects.
> For example ObjectQuery.user_name to get the user_name attribute from
> that query object. But how do I use the relationships that I setup in my
> model classes? I made a class definition where I join two tables(and it
> worked fine, but seems wasteful if there's a better way), because I
> couldn't figure out how to access the relation from the table below.

You should use the ForeignKey construct. Have a look at the SQLAlchemy
docs here, they explain it very well:
http://docs.sqlalchemy.org/en/latest/orm/tutorial.html#building-a-relationship

-- Christoph

[andrew b]

Hey thanks, I've looked at that before. But everytime I try to use the Object.relationship it gives me a NoneType error says I can't append to it etc. Maybe I'm doing something incorrectly. Here's another example of what I'm trying to do.

CODE IN MY ROOT CONTROLLER: 

    c1 = Component()

    v1 = Version()

    c1.version.append(v1)

   

    print c1.version

CODE IN MY MODEL:

class Component(DeclarativeBase):

    __tablename__ = 'component'

    __table_args__ = {}

    #column definitions

    component_pk = Column(u'component_pk', INTEGER(), primary_key=True, nullable=False)

    version_id = Column(u'version_id', INTEGER(), ForeignKey('version.version_id'), nullable=False)

    #relation definitions

    version = relation('Version', primaryjoin='Component.version_id==Version.version_id', backref="user")

    images = relation('Image', primaryjoin='Component.component_pk==component_has_image.c.component_component_pk', secondary=component_has_image, secondaryjoin='component_has_image.c.image_image_pk==Image.image_pk')

    parts = relation('Part', primaryjoin='Component.component_pk==component_has_part.c.component_component_pk', secondary=component_has_part, secondaryjoin='component_has_part.c.part_part_pk==Part.part_pk')

class Version(DeclarativeBase):

    __tablename__ = 'version'

    __table_args__ = {}

    #column definitions

    object_type = Column(u'object_type', VARCHAR(length=45))

    version_id = Column(u'version_id', INTEGER(), primary_key=True, nullable=False)

    version_name = Column(u'version_name', VARCHAR(length=45))

    #relation definitions

    

[Moritz Schlarb]

Your definition implies that there is an one-to-many relationship between Component and Version.

So you can do:

c1.version = v1

Or the other way around:

v1.user.append(c1)