I'm trying to make this many-to-many join work with Flask-SQLAlchemy and two MySQL databases, and it's very close except it's using the wrong database for the join table. Here's the basics...
I've got main_db
and vendor_db
. The tables are setup as main_db.users
, main_db.user_products
(the relation table), and then vendor_db.products
. Should be pretty clear how those are all connected.
in my app.py, I'm seting up the databases like this:
app.config['SQLALCHEMY_DATABASE_URI'] = 'mysql://user:pass@localhost/main_db'
app.config['SQLALCHEMY_BINDS'] = {
'vendor_db': 'mysql://user:pass@localhost/vendor_db'
}
Model definitions are set up like this:
from app import db
# Setup relationship
user_products_tbl = db.Table('user_products', db.metadata,
db.Column('user_id', db.Integer, db.ForeignKey('users.user_id')),
db.Column('product_id', db.Integer, db.ForeignKey('products.product_id'))
)
class User(db.Model):
__tablename__ = 'users'
id = db.Column('user_id', db.Integer, primary_key=True)
products = db.relationship("Product", secondary=user_products_tbl,
backref="users", lazy="dynamic")
class Product(db.Model):
__bind_key__ = 'vendor_db'
__tablename__ = 'products'
id = db.Column('product_id', db.Integer, primary_key=True)
name = db.Column(db.String(120))
The problem is that when I try to get a user's products it's trying to use vendor_db
for the join table instead of main_db
. Any ideas how I can make it use main_db
instead? I've tried setting up another bind to main_db
and setting info={'bind_key': 'main_db'}
on the relationship table definition, but no luck. Thanks!
You add a tags class variable to the Post model. You use the db. relationship() method, passing it the name of the tags model ( Tag in this case). You pass the post_tag association table to the secondary parameter to establish a many-to-many relationship between posts and tags.
Many to Many relationship between two tables is achieved by adding an association table such that it has two foreign keys - one from each table's primary key.
Turns out what I needed to do here was specify the schema in my user_products_tbl
table definition. So,
user_products_tbl = db.Table('user_products', db.metadata,
db.Column('user_id', db.Integer, db.ForeignKey('users.user_id')),
db.Column('product_id', db.Integer, db.ForeignKey('products.product_id')),
schema='main_db'
)
Hope this helps someone else!
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