Collectives™ on Stack Overflow

Find centralized, trusted content and collaborate around the technologies you use most.

Teams

Q&A for work

Connect and share knowledge within a single location that is structured and easy to search.

class DomainRoot(db.Model):
    # Int/Float fields
    id      = db.Column(db.Integer, primary_key=True)
    # String fields
    domain  = db.Column(db.String(64), index=True, unique=True)
    # DateTime fields
    created = db.Column(db.DateTime)
    updated = db.Column(db.DateTime)
    # ForeignKey relationships
    domain_paths = db.relationship('DomainPath', backref='domain_root', lazy='dynamic')
    def __repr__(self):
        return '<DomainRoot %r>' % (self.domain)
class DomainPath(db.Model):
    # Int/Float fields
    id          = db.Column(db.Integer, primary_key=True)
    # String fields
    domain_path = db.Column(db.String(256), index=True, unique=True)
    # DateTime fields
    created     = db.Column(db.DateTime)
    updated     = db.Column(db.DateTime)
    # ForeignKey fields
    domainroot_id = db.Column(db.Integer, db.ForeignKey('domainroot.id'))
    def __repr__(self):
        return '<DomainPath %r>' % (self.domain_path)
When I try to query the DomainRoot object, I get an error:
InvalidRequestError: One or more mappers failed to initialize - can't proceed with initialization of other mappers. Original exception was: Could not determine join condition between parent/child tables on relationship DomainRoot.domain_paths - there are no foreign keys linking these tables. Ensure that referencing columns are associated with a ForeignKey or ForeignKeyConstraint, or specify a 'primaryjoin' expression.
As far as I can tell, I have added the proper foreign key fields.
What am I doing wrong here?
Flask-SQLAlchemy autogenerates the table name domain_root, with an underscore.  You refer to domainroot without the underscore.
In general it's easier to define the fk and relationship in the same model, and avoid using string references.
from flask import Flask
from flask_sqlalchemy import SQLAlchemy
app = Flask(__name__)
db = SQLAlchemy(app)
class DomainRoot(db.Model):
    id = db.Column(db.Integer, primary_key=True)
class DomainPath(db.Model):
    id = db.Column(db.Integer, primary_key=True)
    root_id = db.Column(db.ForeignKey(DomainRoot.id))
    root = db.relationship(DomainRoot, backref='paths')
db.create_all()
db.session.add(DomainRoot(paths=[DomainPath(), DomainPath()]))
db.session.commit()
print(DomainRoot.query.get(1).paths)
[<__main__.DomainPath object at 0x7fc27f443f28>, <__main__.DomainPath object at 0x7fc27f443fd0>]
        
Thanks for contributing an answer to Stack Overflow!
Please be sure to answer the question. Provide details and share your research!
But avoid …
Asking for help, clarification, or responding to other answers.
Making statements based on opinion; back them up with references or personal experience.
To learn more, see our tips on writing great answers.