sqlalchemy many to many relationships (the value of a duplicate key breaks the unique constraint) flask_user role - postgresql

Question

can you help me,
when i run this script it works well
class User(db.Model, UserMixin):
__tablename__ = 'users'
id = db.Column(db.Integer, primary_key=True)
active = db.Column('is_active', db.Boolean(), nullable=False, server_default='1')
# User authentication information. The collation='NOCASE' is required
# to search case insensitively when USER_IFIND_MODE is 'nocase_collation'.
email = db.Column(db.String(255, collation='NOCASE'), nullable=False, unique=True)
email_confirmed_at = db.Column(db.DateTime())
password = db.Column(db.String(255), nullable=False, server_default='')
# User information
first_name = db.Column(db.String(100, collation='NOCASE'), nullable=False, server_default='')
last_name = db.Column(db.String(100, collation='NOCASE'), nullable=False, server_default='')
# Define the relationship to Role via UserRoles
roles = db.relationship('Role', secondary='user_roles')
# Define the Role data-model
class Role(db.Model):
__tablename__ = 'roles'
id = db.Column(db.Integer(), primary_key=True)
name = db.Column(db.String(50), unique=True)
# Define the UserRoles association table
class UserRoles(db.Model):
__tablename__ = 'user_roles'
id = db.Column(db.Integer(), primary_key=True)
user_id = db.Column(db.Integer(), db.ForeignKey('users.id', ondelete='CASCADE'))
role_id = db.Column(db.Integer(), db.ForeignKey('roles.id', ondelete='CASCADE'))
# Setup Flask-User and specify the User data-model
user_manager = UserManager(app, db, User)
# Create all database tables
db.create_all()
# Create 'member#example.com' user with no roles
if not User.query.filter(User.email == 'member#example.com').first():
user = User(
email='member#example.com',
email_confirmed_at=datetime.datetime.utcnow(),
password=user_manager.hash_password('Password1'),
)
db.session.add(user)
db.session.commit()
# Create 'admin#example.com' user with 'Admin' and 'Agent' roles
if not User.query.filter(User.email == 'admin#example.com').first():
user = User(
email='admin#example.com',
email_confirmed_at=datetime.datetime.utcnow(),
password=user_manager.hash_password('Password1'),
)
user.roles.append(Role(name='Admin'))
user.roles.append(Role(name='Agent'))
db.session.add(user)
db.session.commit()
at this stage the code is working without problems but the problem is just after when I add another user with a role that already exists
in this case the Admin role or the Agent role
for example if I add the code below an error message displays
if not User.query.filter(User.email == 'admin2#example.com').first():
user = User(
email='admin2#example.com',
email_confirmed_at=datetime.datetime.utcnow(),
password=user_manager.hash_password('Password1'),
)
user.roles.append(Role(name='Admin'))
user.roles.append(Role(name='Agent'))
db.session.add(user)
db.session.commit()
sqlalchemy.exc.IntegrityError: (psycopg2.IntegrityError) ERREUR: la valeur d'une clé dupliquée rompt la contrainte unique « roles_name_key »
DETAIL: La clé « (name)=(Admin) » existe déjà.
[SQL: 'INSERT INTO roles (name) VALUES (%(name)s) RETURNING roles.id'] [parameters: {'name': 'Admin'}] (Background on this error at: http://sqlalche.
me/e/gkpj)
I tried db driver different (pg8000, pygresql, py-postgresql) and still the same problem,
as the error message shows the problem because of the name value which is unique
name = db.Column (db.String (50), unique = True)
can you explain to me what is the error that I made, and what is the role of this part of code
# Define the relationship to Role via UserRoles
roles = db.relationship ('Role', secondary = 'user_roles')
I use flask with flask_user