Question

I’m using WTforms with Jinja2 and want to change my templates page title depending on whether I am creating a new instance of editing an existing form object.

This is what I wrote in the template:

{% block title %}{% if form.obj %}Edit{% else %}New{% endif %} Post{% endblock %}

What I expect to see:

if the form is filled out I expect to see “Edit Post” in the page title.

if the form is empty I expect to see “New Post” in the page title.

What I get: “New Post” in both instances.

Here is my PostHandler that is passing the form values.

def with_post(fun):
    def decorate(self, post_id=None):
        post = None
        if post_id:
            post = models.BlogPost.get_by_id(int(post_id))
            if not post:
                self.error(404)
                return
        fun(self, post)
    return decorate

class PostHandler(BaseHandler):
    def render_form(self, form):
        self.render_to_response("edit.html", {'form': form})

    @with_post
    def get(self, post):
        self.render_form(MyForm(obj=post))

    @with_post
    def post(self, post):
        form = MyForm(formdata=self.request.POST, obj=post)
        if post and form.validate():
            form.populate_obj(post)
            post.put()
            post.publish()
            self.render_to_response("published.html", {'post': post})
        elif self.request.POST and form.validate():
            post = models.BlogPost()
            post.title = form.title.data
            post.body = form.body.data
            post.tags = form.tags.data
            post.publish()
            self.render_to_response("published.html", {'post': post})
        else:
            self.render_to_response('edit.html', {'form':form})

In short, all I’m trying to do is test whether the form is filled, and change my page title “New Post” or “Edit Post” accordingly.

Answer 1

While Form accepts a obj argument, it doesn’t actually store it, it just uses that obj to fill in any blanks that formdata didn’t provide. So when you ask Jinja2 {% if form.obj %} it’s always going to be False, because there is never a obj property (unless you have a field that happens to be called obj of course).

If you’re editing a post, you’ll have an id to work with so you know which post to update in the database, so where are you currently storing that? Assuming you store it as a hidden field, you could just do:

{% if form.id.data == None %}Must be a New form {% endif %}

If you wanted to check if the entire form was empty, you could access the form.data dictionary, and make sure all the entries are None, although you need to be careful, because I know that FileField returns a u'None' instead of a real None, so you’d have to double check what Fields you care about.