title: SQLalchemy - 'AppenderQuery' object has no attribute 'serialize'
body: <p>So, i'm making a JSON return property in one of my classes, but i get an error when trying to use one of the properties:</p>
  
  <pre><code>class Posts(Base):
      __tablename__ = 'posts'
  
      post_id = Column(Integer, nullable = False, primary_key = True)
      text = Column(String, nullable = False)
      date = Column(DateTime(timezone=True), server_default=func.now())
      deleted = Column(Integer, default = 0)
      owner = Column(Integer, ForeignKey('users.id'))
      owner_rel = relationship('Users')
      comments_rel = relationship('Comments', cascade='all, delete-orphan', lazy='dynamic')
  
      @property
      def serialize(self):
          # Returns Data Object In Proper Format
          return {
              'postID': self.post_id,
              'text': self.text,
              'date': self.date,
              'owner': self.owner,
              'postOwner': self.owner_rel.serialize,
              'comments': self.comments_rel.serialize
          }
  
  
  
  class Comments(Base):
      __tablename__ = 'comments'
  
      comment_id = Column(Integer, nullable = False, primary_key = True)
      post_id = Column(Integer, ForeignKey('posts.post_id'))
      post_rel = relationship('Posts')
      text = Column(String, nullable = False)
      date = Column(DateTime(timezone=True), server_default=func.now())
      deleted = Column(Integer, default = 0)
      owner = Column(Integer, ForeignKey('users.id'))
      owner_rel = relationship('Users')
  
      @property
      def serialize(self):
          # Returns Data Object In Proper Format
          return {
              'commentID': self.comment_id,
              'postID': self.post_id,
              'text': self.text,
              'date': self.date,
              'ownerID': self.owner,
              'owner': self.owner_rel.serialize
          }
  </code></pre>
  
  <p>and i get this error - 'AppenderQuery' object has no attribute 'serialize'</p>
  
  <p>Help?</p>