whitnessme/sqlalchemy_multiple_relationships_between_two_tables

SQLAlchemy Multiple Relationships Between Two Tables

After having difficulty with SQLAlchemy docs on how to get this to work, I finally got assistance to get this correct. So here is this resource to connect a model to another model two times. In the future I will put in instructions for other types.

The 'Two to One' Scenario:

For my flashcard project I had Users and Decks models that I needed to connect twice. A deck has an owner who created it but, if shared, other users can "download" that deck to use and change. I wanted to display who originally created the deck and still have another user who owned this copy of the deck.

The relationships in the Deck Model:

user = db.relationship("User",
       foreign_keys=[user_id],
       back_populates="deck_user")

owner = db.relationship("User",
        foreign_keys=[owner_id],
        back_populates="deck_owner")

The relationships in the User Model:

deck_user = db.relationship("Deck",
            foreign_keys='Deck.user_id',
            back_populates="user",
            lazy='dynamic')

deck_owner = db.relationship("Deck",
             foreign_keys='Deck.owner_id',
             back_populates="owner",
             lazy='dynamic')

In the to_dict method for Deck model:

def  to_dict(self):
     return  {
          "id":  self.id,
          "owner_id":  self.owner_id,
          "user_id":  self.user_id,
          ...
          # code removed for brevity
          }

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