Flask WTForm 动态创建 WTForm 的 SelectField 元素

Question

I have a table in my database that houses some staff and each staff has an allocated task id . I want to dynamically create select fields according to the number of staff that has a particular task id. For example, if there are 3 staff with task id 1 , there will be three select fields (with 5 dropdown items each) In form.py

 class DynamicForm(Form):
    @classmethod 
    def append_field(cls, name, field):
        setattr(cls, name, field)
        return cls  

In routes.py -- main file

assigns = Project_Users.query.filter_by(project_id=id).all() 
// query the database to get all the staff under the project using the project id 
l = len(assigns) // length/ number of staff

d = DynamicForm() // from form.py
for e in range(l):         
  d.append_field(assigns[e].admin.first_name,SelectField(assigns[e].admin.first_name, validators=[DataRequired()], choices=[('0', 'No Task'),( '1','Site Acquisition'),('2','Installation'),('3','Configuration'), ('4','Commission')]))

    d.append_field('submit', SubmitField('SAVE')) // this is outside the for loop

In html template

<form action="/project/{{ project.id }}/tasks" method="POST">
                  {{ d.hidden_tag() }}
                <table class="table is-stripped" style="width: 100%;">
                    <tbody>
                      {% for g in d %}
                      <tr>
                        <td>{{ g.label }}</td>
                        <td>{{ g }}</td>
                      </tr>
                      {% endfor %}

                      </tbody>
                  </table>
              </form>

The codes above is working, but it does not change and the number of staff changes for example, project 1 has 3 staff and it rendered three selectfields but when project 2 which has 2 staff is rendered 3 staff and 3 selectfields appears

Answer 1

Try constructing your form dynamically overwriting the constructor with arguments:

class DynamicForm(Form):
    submit = SubmitField

    def __init__(self, **kwargs):
        assigns = Project_Users.query.filter_by(project_id=kwargs['id']).all()
        for ass in assigns:         
            setattr(DynamicForm,
                    ass.admin.first_name,
                    SelectField(ass.admin.first_name, 
                                validators=[DataRequired()], 
                                choices=[('0', 'No Task'),
                                         ( '1','Site Acquisition'),
                                         ('2','Installation'),
                                         ('3','Configuration'),
                                         ('4','Commission')]))
        super().__init__()

Then you call it like

d = DynamicForm(id=1)

Technically the difference between this and your form is that you add class level attributes after you have initialised the form, and after the base Form has run. Ie there is a difference between:

DynamicForm(Form):
    def __init__(self)
        super().__init__() # calls Form.__init__()
        # extra stuff

and

DynamicForm(Form):
    def __init__(self)
        # extra stuff
        super().__init__() # calls Form.__init__() and acts on extra stuff.