python - SQLAlchemy Many-to-Many Relationship on a Single Table Error: NoReferencedTableError -

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i'm using flask , sqlalchemy.

i'm trying reference column in same table create tree structure, using additional table store ancestor-child connections, not parent-child.

i've used example here https://stackoverflow.com/a/5652169/2947812, , code in models.py is:

# -*- coding: utf-8 -*- my_app import db      cats_hierarchies = db.table('cats_hierarchies', db.metadata(),         db.column('parent_id', db.integer, db.foreignkey('category.id')),         db.column('category_id', db.integer, db.foreignkey('category.id'))         )  class category(db.model):     __tablename__ = 'category'      id = db.column(db.integer, primary_key=true)     children = db.relationship("category",         secondary = cats_hierarchies,         primaryjoin = cats_hierarchies.c.category_id == id,         secondaryjoin = cats_hierarchies.c.parent_id == id,         backref="children")

when try create database from my_app import db receive following error message: sqlalchemy.exc.noreferencedtableerror: foreign key associated column 'cats_hierarchies.category_id' not find table 'category' generate foreign key target column 'id'

what doing wrong?

i got rid of error adding 

foreign_keys =    [cats_hierarchies.c.parent_id,    cats_hierarchies.c.category_id])

to category.children definition.

still don't know though why necessary. found here: https://stackoverflow.com/a/8809907/2947812


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