Flask Sqlalchemy circular import when using blueprints

Question

I have a flask application which it's packages are separated each other using Blueprints. I have 3 packages which have many to one relations.

The first package (blueprint) is Authentication (Containts User_Model):

from Billboard.Apps.models import Android_Model
from Billboard.Survey.models import Survey_Model

class User_Model (db.Model, UserMixin):
    __tablename__ = user_model
    ...
    advertised_apps = db.relationship ('Android_Model' , backref = 'user_model' , lazy = True)
    advertised_surveys = db.relationship ('Survey_Model' , backref = 'user_model' , lazy = True)

the second package has foreign key to my User_Model:

from Billboard.Authentication.models import User_Model

class Survey_Model (db.Model):
    __tablename__ = 'survey_model'
    ...
    advertiser_id = db.Column(db.Integer, db.ForeignKey('user_model.id'), nullable=False)

And the third package's model is same as second one.

When i run my flask app i got some imports error which i know they are for circular import between these models.

NOTE: when i remove this relation between these models, i got no error and project works correctly.

Any idea to solve?

jxpp jxpp · Accepted Answer · 2018-12-04T14:05:33

You don't actually need to import the model to declare a relationship with it. Notice db.relationship takes a string as a first argument and not a class.

Flask Sqlalchemy circular import when using blueprints

1 Answers