SQLAlchemy ORM load_only colomns with multiple join

Question

Now i have:

class DeviceModel(db.Model):

    id = db.Column(db.Integer, primary_key=True)
    vendor = db.Column(db.String, nullable=False)
    model = db.Column(db.String, nullable=False)
    group_id = db.Column(db.ForeignKey('device_group.id', ondelete='SET NULL'), nullable=True)

class DeviceGroup(db.Model):
    id = db.Column(db.Integer, primary_key=True)
    name = db.Column(db.String, nullable=False, unique=True)
    device_type_id = db.Column(db.ForeignKey('device_type.id', ondelete='SET NULL'), nullable=True)
    device_type = db.relationship("DeviceType", lazy='joined')

class DeviceType(db.Model):

    id = db.Column(db.Integer, primary_key=True)
    name = db.Column(db.String, nullable=False, unique=True)

How can i query only DeviceModel.id, DeviceType.name fields?

In pure sql it was:

SELECT device_model.id               AS device_model_id,
       device_type_1.name            AS device_type_1_name
FROM device_model
       LEFT OUTER JOIN device_group AS device_group_1 ON device_group_1.id = device_model.group_id
       LEFT OUTER JOIN device_type AS device_type_1 ON device_type_1.id = device_group_1.device_type_id;

score 2 · Answer 1 · answered Sep 14 '18 at 10:44

2

A Cup of tea creates magic, I answer myself

records = db.session.query(DeviceModel.id,DeviceType.name).join(DeviceGroup).join(DeviceType).all()

answered Sep 14 '18 at 10:44

al_platonov

101
1
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SQLAlchemy ORM load_only colomns with multiple join

1 Answers1