Auto increment non primary column in SQLAlchemy - postgresql

Question

In my db model I need userId and forumPostId to be a composite primary key. But I need id to be a auto incremented value. But when I'm trying to insert new row in table getting none in id instead of a auto incremented integer.
class ForumPostFollow(db.Model):
__tablename__ = "forum_post_follow"
id = db.Column(db.Integer,autoincrement=True,nullable=False,unique=True)
userId = db.Column(db.Integer,db.ForeignKey('user.id'),primary_key=True)
forumPostId = db.Column(db.Integer,db.ForeignKey('forum_post.id'),primary_key=True)
active = db.Column(db.Boolean,nullable=False)
My package versions
Flask-SQLAlchemy==2.3.2 SQLAlchemy>=1.3.0
This question is similar to this question. But it's for version 1.1
Updated Question
I've changed my id columns sequence from terminal
ALTER TABLE forum_post_follow DROP COLUMN id;
ALTER TABLE forum_post_follow ADD COLUMN id SERIAL;
Then my altered columns looks like this
But still getting same error
sqlalchemy.exc.IntegrityError: (psycopg2.errors.NotNullViolation) null value in column "id" violates not-null constraint
DETAIL: Failing row contains (1, 1, t, null).
[SQL: INSERT INTO forum_post_follow (id, "userId", "forumPostId", active) VALUES (%(id)s, %(userId)s, %(forumPostId)s, %(active)s)]
[parameters: {'id': None, 'userId': 1, 'forumPostId': 1, 'active': True}]

Answer 1

I had a similar problem and found that as per SQLAlchemy 1.3 Documentation:
For the case where this default generation of IDENTITY is not desired, specify False for the Column.autoincrement flag, on the first integer primary key column:
so you might want to try this:
class ForumPostFollow(db.Model):
__tablename__ = "forum_post_follow"
id = db.Column(db.Integer,autoincrement=False,primary_key=True,nullable=False,unique=True)
userId = db.Column(db.Integer,db.ForeignKey('user.id'),primary_key=True)
forumPostId = db.Column(db.Integer,db.ForeignKey('forum_post.id'),primary_key=True)
active = db.Column(db.Boolean,nullable=False)