Flask Sqlalchemy association table overwrites data

Question

I have created an api where the user will send me the user_id and branch_id/branches_id and my api will insert records in my association table. e.g My post request is

{

    "branches" :  [2,3,4],
    "user_id" : 1

}

Result is

#   user_id branch_id
1   1   2
2   1   3
3   1   4

My next post request is

{

    "branches" :  [1],
    "user_id" : 1

}

Here my association table gets overwritten

#   user_id branch_id
1   1   1

This is my Code snippet :

def post(self):       
    branch_ids = request.json['branches']
    user_id = request.json['user_id'] 
    if type(branch_ids)!= list :
        branch_ids = [branch_ids]
    branches = db.session.query(Branch).filter(Branch.id.in_(branch_ids)).all()
    if len(branch_ids) != len(branches):
        return "please select valid branches"
    user = db.session.query(User).filter(User.id == user_id).first()
    print(user)
    if user != None :
        user.branches = [branch for branch in branches]
        db.session.commit()
    else:
        return "user not found"
    return "done"

I want to assign branches to users and also i want to remove branches from users.

Answer 1

I wasn't appending to my table

for branch in branches_id:
    user.branches.append(branch)