I have a model Region
and each Region
can have sub-regions. Each sub-region has a field parent_id
which is the id of its parent region. Here is how my model looks like
class Region(db.Model):
__tablename__ = 'regions'
__table_args__ = {'schema': 'schema_name'}
id = db.Column(db.Integer, primary_key=True)
name = db.Column(db.String(100))
parent_id = db.Column(db.Integer, db.ForeignKey('regions.id'))
parent = db.relationship('Region', primaryjoin=('Region.parent_id==Region.id'), backref='sub-regions')
created_at = db.Column(db.DateTime, default=db.func.now())
deleted_at = db.Column(db.DateTime)
Bu when i try to do db.create_all
i get this error sqlalchemy.exc.NoReferencedTableError: Foreign key associated with column 'regions.parent_id' could not find table 'regions' with which to generate a foreign key to target column 'id'
Why cant it find regions
when i am specifying it in __tablename__
? I am using flask-sqlalchemy version 1.0
EDIT -- i removed the line
__table_args__ = {'schema': 'schema_name'}
from my code and it works. Beats the hell out of me.
I had the same issue with the schema name argument. What I changed to get it to work was to reference the table class directly in ForeignKey and relationships instead of using a string. Example:
parent_id = Column(Integer, ForeignKey(Region.id), index=True)
parent = relationship(lambda: Region, remote_side=id, backref='sub_regions')
You must tell SQLAlchemy what the "remote side" of the relationship is, to distinguish between the current row and the row being joined to. The relevant explanation is located partway into this section of the documentation on relationships.
The relationship might look like this:
parent = db.relationship('Region', remote_side=id, backref='sub_regions')
This is an example demonstrating a self-referential relationship:
from sqlalchemy import Column, Integer, String, ForeignKey
from sqlalchemy.engine import create_engine
from sqlalchemy.ext.declarative.api import declarative_base
from sqlalchemy.orm import sessionmaker, relationship
engine = create_engine('sqlite:///:memory:', echo=True)
Session = sessionmaker(engine)
Base = declarative_base(engine)
session = Session()
class Region(Base):
__tablename__ = 'region'
id = Column(Integer, primary_key=True)
name = Column(String, nullable=False)
parent_id = Column(Integer, ForeignKey('region.id'), index=True)
parent = relationship(lambda: Region, remote_side=id, backref='sub_regions')
Base.metadata.create_all()
r1 = Region(name='United States of America')
r2 = Region(name='California', parent=r1)
session.add_all((r1, r2))
session.commit()
ca = session.query(Region).filter_by(name='California').first()
print ca.parent.name
There will be many lines of SQL output since echo is on, and the script will print 'United States of America' at the end.
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