SQLAlchemy ManyToMany secondary table with additional fields

You will have to switch from using a plain, many-to-many relationship to using an "Association Object", which is basically just taking the association table and giving it a proper class mapping. You'll then define one-to-many relationships to User and Community:

class Membership(db.Model):    __tablename__ = 'community_members'    id = db.Column('id', db.Integer, primary_key=True)    user_id = db.Column(db.Integer, db.ForeignKey('user.id'))    community_id = db.Column(db.Integer, db.ForeignKey('community.id'))    time_create = db.Column(db.DateTime, nullable=False, default=func.now())    community = db.relationship(Community, backref="memberships")    user = db.relationship(User, backref="memberships")class Community(db.Model):    __tablename__ = 'community'    id = db.Column(db.Integer, primary_key=True)    name = db.Column(db.String(100), nullable=False, unique=True)

But you may only occasionally be interested in the create time; you want the old relationship back! well, you don't want to set up the relationship twice; because sqlalchemy will think that you somehow want two associations; which must mean something different! You can do this by adding in an association proxy.

from sqlalchemy.ext.associationproxy import association_proxyCommunity.members = association_proxy("memberships", "user")User.communities = association_proxy("memberships", "community")

If you only need query community_members and community table by a known user_id(such as user_id=2), In SQLAlchemy, you can perform:

session.query(community_members.c.time_create, Community.name).filter(community_members.c.user_id==2)

to get the result.