title: Can't create records in SQLAlchemy due to One or more mappers failed to initialize
body: <p>I have a model file (simplified)</p>
  
  <p>Repos have single user, and users can have multiple repos.</p>
  
  <pre><code>class Repo(Base):
      __tablename__ = "repos"
  
      id = db.Column(db.Integer, primary_key=True)
      name = db.Column(db.String(512), unique=True)
      user_id = Column(Integer, ForeignKey('users.id'))
      user = db.relationship("User", back_populates="users")
  
  class User(Base):
      __tablename__ = 'users'
  
      id = db.Column(db.Integer, primary_key=True)
      name = db.Column(db.String(200), unique=True)
      repos = db.relationship("User", back_populates="repos")
  </code></pre>
  
  <p>When I try to insert a record I get the error:</p>
  
  <blockquote>
    <p>One or more mappers failed to initialize - can't proceed with initialization of other mappers.  Original exception was: Mapper 'Mapper|User|users' has no property 'users'</p>
  </blockquote>
  
  <p>How can I fix my model? </p>