What's the best practice in WTForms, using one form class or multiple ones?

Question

I've got very simple forum. On one page - list of topics with posting form to create topics:

<form action="" method="post" name="PostForm">
    {{form.hidden_tag()}}
    {{form.topic(placeholder='New topic'}}
    {{form.message(placeholder='Enter your text here'}}
    <input type="submit">
</form>

The other page - topic page with form for posting message in topic:

<form action="" method="post" name="PostForm">
    {{form.hidden_tag()}}
    {{form.message(placeholder='Enter your text here'}}
    <input type="submit">
</form>

And I've got form class for all:

class PostingForm(Form):
    topic = TextField(validators=[DataRequired()])
    message = TextAreaField(validators=[DataRequired()])

But on the topic page (there is no input "topic") I can't pass validate_on_submit.

So what is the best way here - create two classes to separate topic and message inputs or somehow block validatation for topic input on the second page?

Answer 1

There are three different ways to do this (all of them acceptable):

1. Use two different forms:

   class PostMessageForm(Form):
       message = TextAreaField(validators=[DataRequired()])
   
   class CreateTopicForm(PostMessageForm):
       topic = TextField(validators=[DataRequired()])
   

2. Delete the field:

   # In the controller that handles topic messages
   form = PostingForm()
   del form.topic
   if form.validate_on_submit():
       # etc.
   

3. Alter the validators:

   # In the controller that handles topic messages
   form = PostingForm()
   
   # Either mark the field as optional
   form.topic.validators.insert(0, Optional())
   
   # or remove the validator entirely
   form.topic.validators = []