Adding to a Many to Many relationship with SQLAlchemy

Question

Premise: Search public comments (a string) for instances of items from a predetermined list. There can be multiple list matches within a single comment.

I am trying to use a Many to Many structure to keep track of this.

I have created the following database structure using SQLAlchemy (Python 3.5)

reddit_assoc = Table('reddit_assoc', Base.metadata,
    Column('comment_id', Integer, ForeignKey('reddit_comments.comment_id')),
    Column('character_id', Integer, ForeignKey('characters.character_id'))
    )

class characters(Base):
    __tablename__ ='characters'

    character_id = Column(VARCHAR(20),primary_key=True)
    name = Column(VARCHAR(3072))
    added = Column('added', DateTime, default=datetime.datetime.now())
    reddit_mentions = relationship('reddit_comments', secondary='reddit_assoc', back_populates='character_mentions')

class reddit_comments(Base):
    __tablename__ = 'reddit_comments'
    comment_id = Column(VARCHAR(50), primary_key=True)
    comment_author = Column(VARCHAR(300))
    comment_created = Column(VARCHAR(300))
    link_id = Column(VARCHAR(50))
    subreddit_id = Column(VARCHAR(50))
    character_mentions = relationship('characters', secondary='reddit_assoc', back_populates='reddit_comments')

And using the following to find matches

def char_counter(comment):
    Session = DBSession()
    reader = Session.query(characters).all()

    for char in reader:
        if char[0] in comment['comment_body'] or char[1] in comment['comment_body']:
            # We have a match. Add to database.
            Session.merge(reddit_comments(#relevant information from comment#))
            #How do I add to the Many to Many here?
            Session.commit()
        Session.close()

Problem: Looking at the comment in the above snippet, I don't understand how I add the relationship of potentially multiple character matches from the comment['comment_body'] string into the reddit_assoc assocation table correctly. Can someone please advise further?

Answer 1

Relationships that you are using in this case behave as a list. So you need to add newly created reddit comment to list reddit_mentions .

def char_counter(comment):
    Session = DBSession()
    reader = Session.query(characters).all()

    for char in reader:
        if char[0] in comment['comment_body'] or char[1] in comment['comment_body']:
            # We have a match. Add to database.
            rc = reddit_comments(#relevant information from comment#)
            Session.flush()  # to ensure you have primary key, although may not be needed
            char.reddit_mentions.append(rc)  # this will eventually fill your reddit_assoc table
            Session.add(char)

    # move this outside of loop        
    Session.commit()
    Session.close()