Python Flask: How to correctly query a select field?

Question

I want to build the selectable drop button to select the users in the database according to users' role id.

The classes are defined below.

roles_users = db.Table(
   'roles_users',
   db.Column('user_id', db.Integer(), db.ForeignKey('user.id')),
   db.Column('role_id', db.Integer(), db.ForeignKey('role.id'))
)


class Role(db.Model, RoleMixin):
     id = db.Column(db.Integer(), primary_key=True)
     name = db.Column(db.String(80), unique=True)

     def __str__(self):
        return self.name

class User(db.Model, UserMixin):
     id = db.Column(db.Integer, primary_key=True)
     roles = db.relationship('Role', secondary=roles_users,
                         backref=db.backref('users', lazy='dynamic'))
     email = db.Column(db.String(255), unique=True)

     def __str__(self):
         return self.email
 
class Project(db.Model):

     id = db.Column(db.Integer, primary_key=True)
     reviewer = db.Column(db.Unicode(128))

     def __unicode__(self):
        return self.name

Since I want to list the users with Role.id==4 as reviewer in project class, I tried both methods below but in vain:

1. QuerySelectField

It returns nothing in the list:

def reviewer_choices():
    return User.query.join(User.roles).filter(Role.id == 4).all().query

class Project(db.Model):
     reviewer = QuerySelectField(query_factory = reviewer_choices)

2. form_args

It returns error: TypeError: __init__() got an unexpected keyword argument 'query_factory'

def reviewer_choices():
    return User.query.join(User.roles).filter(Role.id == 4).all().query

class Project(db.Model):
    form_args = dict(
              reviewer=dict(query_factory =reviewer_choices),
   )

Answer 1

query_factory callback should return a query, you could change your reviewer_choices like this:

def reviewer_choices():
    return User.query.join(User.roles).filter(Role.id == 4)

Update:

Add below code with two selected required fields to your class SWProjectView(sqla.ModelView):

form_extra_fields = {
    'reviewer1': sqla.fields.QuerySelectField(
        label='Reviewer1',
        query_factory=reviewer1_choices,
        validators=[DataRequired()]
    ),
    'reviewer2': sqla.fields.QuerySelectField(
        label='Reviewer2',
        query_factory=reviewer2_choices,
        validators=[DataRequired()]
    )
}

This will make the field Reviewer1 and Reviewer2 to be selected and required fields, show in the image: