title: Flask sqlalchemy many-to-many insert data
body: <p>I am trying to make a many to many relation here in <strong>Flask-SQLAlchemy</strong>, but it seems that I don't know how to fill the <em>"many to many identifier database"</em>. Could you please help me understand what I am doing wrong and how it is supposed to look?</p>
  
  <pre class="lang-python prettyprint-override"><code>class User(db.Model):
      __tablename__ = 'users'
      user_id = db.Column(db.Integer, primary_key=True)
      user_fistName = db.Column(db.String(64))
      user_lastName = db.Column(db.String(64))
      user_email = db.Column(db.String(128), unique=True)
  
  
  class Class(db.Model):
      __tablename__ = 'classes'
      class_id = db.Column(db.Integer, primary_key=True)
      class_name = db.Column(db.String(128), unique=True)
  </code></pre>
  
  <p>and then my identifier database:</p>
  
  <pre><code>student_identifier = db.Table('student_identifier',
      db.Column('class_id', db.Integer, db.ForeignKey('classes.class_id')),
      db.Column('user_id', db.Integer, db.ForeignKey('users.user_id'))
  )
  </code></pre>
  
  <p>so far it looks like this when I try to insert the data into the database. </p>
  
  <pre><code># User
  user1 = User(
              user_fistName='John',
              user_lastName='Doe',
              user_email='john@doe.es')
  
  user2 = User(
              user_fistName='Jack',
              user_lastName='Doe',
              user_email='jack@doe.es')
  
  user3 = User(
              user_fistName='Jane',
              user_lastName='Doe',
              user_email='jane@doe.es')
  
  db.session.add_all([user1, user2, user3])
  db.session.commit()
  
  # Class
  cl1 = Class(class_name='0A')
  cl2 = Class(class_name='0B')
  cl3 = Class(class_name='0C')
  cl4 = Class(class_name='Math')
  cl5 = Class(class_name='Spanish')
  db.session.add_all([cl1, cl2, cl3, cl4, cl5])
  db.session.commit()
  </code></pre>
  
  <p>Now my problem is, how do I add to the many to many database, since I really can't create a 'student_identifier' object? If I could it could perhaps have looked like this:</p>
  
  <pre><code># Student Identifier
  sti1  = StiClass(class_id=cl1.class_id, class_name=user1.user_id)
  sti2  = StiClass(class_id=cl3.class_id, class_name=user1.user_id)
  sti3  = StiClass(class_id=cl4.class_id, class_name=user1.user_id)
  sti4  = StiClass(class_id=cl2.class_id, class_name=user2.user_id)
  db.session.add_all([sti1, sti2, sti3, sti4])
  db.session.commit()
  </code></pre>
  
  <p>How I am supposed to insert into a many to many table with ORM?</p>