sqlalchemy.exc.ProgrammingError: (psycopg2.errors.InvalidForeignKey) there is no unique constraint matching given keys for referenced table "dicom"

Question

Basically on flask app server in models.py you use classes to call ORM on PostgreSQL however if you do one to one relations or one to many relationship. you can get a error if your do not defined your key as Unique. In postgresql all foreign keys must reference a unique key in the parent table, so in your bar table you must have a unique (name) index.Finally, we should mention that a foreign key must reference columns that either are a primary key or form a unique constraint.

Traceback (most recent call last):
  File "d:\l_pipe\vessel_app_celery\vessel_env\lib\site-packages\sqlalchemy\engine\base.py", line 1248, in _execute_context
    cursor, statement, parameters, context
  File "d:\l_pipe\vessel_app_celery\vessel_env\lib\site-packages\sqlalchemy\engine\default.py", line 588, in do_execute
    cursor.execute(statement, parameters)
psycopg2.errors.InvalidForeignKey: there is no unique constraint matching given keys for referenced table "dicom"     


The above exception was the direct cause of the following exception:

Traceback (most recent call last):
  File "C:\Users\lesli\AppData\Local\Programs\Python\Python37\lib\runpy.py", line 193, in _run_module_as_main
    "__main__", mod_spec)
  File "C:\Users\lesli\AppData\Local\Programs\Python\Python37\lib\runpy.py", line 85, in _run_code
    exec(code, run_globals)
  File "D:\L_pipe\vessel_app_celery\vessel_env\Scripts\flask.exe\__main__.py", line 9, in <module>
  File "d:\l_pipe\vessel_app_celery\vessel_env\lib\site-packages\flask\cli.py", line 990, in main
    cli.main(args=sys.argv[1:])
  File "d:\l_pipe\vessel_app_celery\vessel_env\lib\site-packages\flask\cli.py", line 596, in main
    return super().main(*args, **kwargs)
  File "d:\l_pipe\vessel_app_celery\vessel_env\lib\site-packages\click\core.py", line 1062, in main
    rv = self.invoke(ctx)
  File "d:\l_pipe\vessel_app_celery\vessel_env\lib\site-packages\click\core.py", line 1668, in invoke
    return _process_result(sub_ctx.command.invoke(sub_ctx))
  File "d:\l_pipe\vessel_app_celery\vessel_env\lib\site-packages\click\core.py", line 1668, in invoke
    return _process_result(sub_ctx.command.invoke(sub_ctx))
  File "d:\l_pipe\vessel_app_celery\vessel_env\lib\site-packages\click\core.py", line 1404, in invoke
    return ctx.invoke(self.callback, **ctx.params)
  File "d:\l_pipe\vessel_app_celery\vessel_env\lib\site-packages\click\core.py", line 763, in invoke
    return __callback(*args, **kwargs)
  File "d:\l_pipe\vessel_app_celery\vessel_env\lib\site-packages\click\decorators.py", line 26, in new_func
    return f(get_current_context(), *args, **kwargs)
  File "d:\l_pipe\vessel_app_celery\vessel_env\lib\site-packages\flask\cli.py", line 440, in decorator
    return __ctx.invoke(f, *args, **kwargs)
  File "d:\l_pipe\vessel_app_celery\vessel_env\lib\site-packages\click\core.py", line 763, in invoke
    return __callback(*args, **kwargs)
  File "d:\l_pipe\vessel_app_celery\vessel_env\lib\site-packages\flask_migrate\cli.py", line 134, in upgrade
    _upgrade(directory, revision, sql, tag, x_arg)
  File "d:\l_pipe\vessel_app_celery\vessel_env\lib\site-packages\flask_migrate\__init__.py", line 95, in wrapped
    f(*args, **kwargs)
  File "d:\l_pipe\vessel_app_celery\vessel_env\lib\site-packages\flask_migrate\__init__.py", line 280, in upgrade     
    command.upgrade(config, revision, sql=sql, tag=tag)
  File "d:\l_pipe\vessel_app_celery\vessel_env\lib\site-packages\alembic\command.py", line 298, in upgrade
    script.run_env()
  File "d:\l_pipe\vessel_app_celery\vessel_env\lib\site-packages\alembic\script\base.py", line 489, in run_env        
    util.load_python_file(self.dir, "env.py")
  File "d:\l_pipe\vessel_app_celery\vessel_env\lib\site-packages\alembic\util\pyfiles.py", line 98, in load_python_file
    module = load_module_py(module_id, path)
  File "d:\l_pipe\vessel_app_celery\vessel_env\lib\site-packages\alembic\util\compat.py", line 184, in load_module_py 
    spec.loader.exec_module(module)
  File "<frozen importlib._bootstrap_external>", line 728, in exec_module
  File "<frozen importlib._bootstrap>", line 219, in _call_with_frames_removed
  File "migrations\env.py", line 96, in <module>
    run_migrations_online()
  File "migrations\env.py", line 90, in run_migrations_online
    context.run_migrations()
  File "<string>", line 8, in run_migrations
  File "d:\l_pipe\vessel_app_celery\vessel_env\lib\site-packages\alembic\runtime\environment.py", line 846, in run_migrations
    self.get_context().run_migrations(**kw)
  File "d:\l_pipe\vessel_app_celery\vessel_env\lib\site-packages\alembic\runtime\migration.py", line 520, in run_migrations
    step.migration_fn(**kw)
  File "D:\L_pipe\vessel_app_celery\Vessel-app\Back-end\migrations\versions\9ea0138f3052_.py", line 228, in upgrade   
    sa.PrimaryKeyConstraint('id')
  File "<string>", line 8, in create_table
  File "<string>", line 3, in create_table
  File "d:\l_pipe\vessel_app_celery\vessel_env\lib\site-packages\alembic\operations\ops.py", line 1252, in create_table
    return operations.invoke(op)
  File "d:\l_pipe\vessel_app_celery\vessel_env\lib\site-packages\alembic\operations\base.py", line 374, in invoke     
    return fn(self, operation)
  File "d:\l_pipe\vessel_app_celery\vessel_env\lib\site-packages\alembic\operations\toimpl.py", line 101, in create_table
    operations.impl.create_table(table)
  File "d:\l_pipe\vessel_app_celery\vessel_env\lib\site-packages\alembic\ddl\impl.py", line 258, in create_table      
    self._exec(schema.CreateTable(table))
  File "d:\l_pipe\vessel_app_celery\vessel_env\lib\site-packages\alembic\ddl\impl.py", line 140, in _exec
    return conn.execute(construct, *multiparams, **params)
  File "d:\l_pipe\vessel_app_celery\vessel_env\lib\site-packages\sqlalchemy\engine\base.py", line 984, in execute     
    return meth(self, multiparams, params)
  File "d:\l_pipe\vessel_app_celery\vessel_env\lib\site-packages\sqlalchemy\sql\ddl.py", line 72, in _execute_on_connection
    return connection._execute_ddl(self, multiparams, params)
  File "d:\l_pipe\vessel_app_celery\vessel_env\lib\site-packages\sqlalchemy\engine\base.py", line 1046, in _execute_ddl
    compiled,
  File "d:\l_pipe\vessel_app_celery\vessel_env\lib\site-packages\sqlalchemy\engine\base.py", line 1288, in _execute_context
    e, statement, parameters, cursor, context
  File "d:\l_pipe\vessel_app_celery\vessel_env\lib\site-packages\sqlalchemy\engine\base.py", line 1482, in _handle_dbapi_exception
    sqlalchemy_exception, with_traceback=exc_info[2], from_=e
  File "d:\l_pipe\vessel_app_celery\vessel_env\lib\site-packages\sqlalchemy\util\compat.py", line 178, in raise_      
    raise exception
  File "d:\l_pipe\vessel_app_celery\vessel_env\lib\site-packages\sqlalchemy\engine\base.py", line 1248, in _execute_context
    cursor, statement, parameters, context
  File "d:\l_pipe\vessel_app_celery\vessel_env\lib\site-packages\sqlalchemy\engine\default.py", line 588, in do_execut    cursor.execute(statement, parameters)
sqlalchemy.exc.ProgrammingError: (psycopg2.errors.InvalidForeignKey) there is no unique constraint matching given keys for referenced table "dicom"

[SQL:
CREATE TABLE "DicomFormData" (
        id SERIAL NOT NULL,
        session_id VARCHAR(200) NOT NULL,
        date_uploaded TIMESTAMP WITHOUT TIME ZONE NOT NULL,
        study_name VARCHAR(300) NOT NULL,
        description VARCHAR(1000) NOT NULL,
        PRIMARY KEY (id),
)

]

Answer 1

Solution need to add table args with db.Unique Constraint

class Dicom(db.Model):
    
    __tablename__ = 'dicom'
    ## data unqine id 
    __table_args__ = (
        # this can be db.PrimaryKeyConstraint if you want it to be a primary key
        db.UniqueConstraint('session_id'),
    )

    id = db.Column(db.Integer, primary_key=True)  
    date_uploaded = db.Column(db.DateTime, nullable=False, default=datetime.utcnow) 
    user_id = db.Column(db.Integer, db.ForeignKey('user.id'), nullable=False)
    userReact_id = db.Column(db.Integer, db.ForeignKey('UserReact.id'), nullable=True)
    dicom_stack = db.Column(db.LargeBinary, nullable=False)
    thumbnail = db.Column(db.LargeBinary, nullable=False)
    file_count = db.Column(db.Integer, nullable=True) 
    session_id = db.Column(db.String(200), nullable=False)
     #uselist one to one relationship
    formData = db.relationship('DicomFormData', uselist=True, backref='author', lazy=True)
  
    def __repr__(self):
        return f"Dicom('{self.date_uploaded}')"

class DicomFormData(db.Model):

    id = db.Column(db.Integer, primary_key=True)  
    date_uploaded = db.Column(db.DateTime, nullable=False, default=datetime.utcnow) 
    study_name = db.Column(db.String(300), nullable=False) 
    description = db.Column(db.String(1000), nullable=False)
    session_id = db.Column(db.String(200), db.ForeignKey('dicom.session_id'), nullable=False)

    def __repr__(self):
        return f"DicomFormData('{self.study_name}')"