Check for string in queryset within a Django template

Question

I know this should be straight-forward, but for some reasons I'm not getting the results I want.

This instruction: {{user.profile.role.all}} in my Django template outputs this:

<QuerySet [<Role: Creator>, <Role: Performer>, <Role: Venue>]>

I'd like to check if a role is within this queryset; so, for instance, if I want to check if a role 'venue' is present, according to what the documentation tells me, I should do:

{% if "Venue" in user.profile.role.all %}

Right? The above-mentioned if, though, returns false. Why is that?

Because a string is something different than a Role with the given name? — Willem Van Onsem, Jun 01 '20 at 18:45
OK, thanks. So, would that be better for me to build a list (of strings) in the view first, since I'll be doing this check a few times in the template? — HBMCS, Jun 01 '20 at 18:49
probably better a set of strings, since that has *O(1)* average lookup time. — Willem Van Onsem, Jun 01 '20 at 18:53
sorry, I'm a bit lost. What is a 'set of strings'? If this is what I have in my view: `context['role'] = Role.objects.filter(profile__id=self.get_object().id)`, how would I do that? — HBMCS, Jun 01 '20 at 19:01
Very simple: `class Role(models.Model): type= models.CharField(max_length=30) def __str__(self): return self.type` — HBMCS, Jun 01 '20 at 19:03
Linked to the user with `role = models.ManyToManyField(Role, blank=True)` from the User model. — HBMCS, Jun 01 '20 at 19:04

score 1 · Accepted Answer · answered Jun 01 '20 at 19:05

1

The reason this does not work is because a string is something different than a Role with as name the same string.

You can pass a set of role names to the template, for example with:

context['role'] = Role.objects.filter(
    profile__user=self.request.user
).values_list('type', flat=True)

answered Jun 01 '20 at 19:05

Willem Van Onsem

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Yes, that does it! Thanks. – HBMCS Jun 01 '20 at 19:08
Wait, but why does `{% if "Venue" or "Promoter" in roleList %}` return true then, if either one or the other are in the list? Can't I check for more than one string at a time? – HBMCS Jun 01 '20 at 19:16
@HBMCS: that is because the *truthiness* of `'Venue'` is true since it is a non-empty string, you write `if ('Venue') or ('Promotor' in roleList %}` after all, you should write it as `{% if 'Venue' in roleList or 'Promotor' in roleList %}`. – Willem Van Onsem Jun 01 '20 at 19:18
This works: (i.e. returns false) `{% if "Venue" in roleList or "Promoter" in roleList %}` although it doesn't seem very DRY to me. – HBMCS Jun 01 '20 at 19:18
Ah, OK, so if I'm checking for ten roles I need to repeat in roleList each time. OK, I'll do that. – HBMCS Jun 01 '20 at 19:19
@HBMCS: Django has a permissions framework that is probaby better: https://stackoverflow.com/questions/9469590/check-permission-inside-a-template-in-django it makes use of `Groups`, so perhaps you can use the permissions framework over writing your own. – Willem Van Onsem Jun 01 '20 at 19:20
This is checking the properties of Profiles for displaying it to anonymous users, otherwise it'd have been too easy :) . Like, 'do not display the instruments played tab in the profile page of a composer' sort of thing. – HBMCS Jun 01 '20 at 19:40
...or maybe you mean that 'Groups' should be my 'Roles'? – HBMCS Jun 01 '20 at 19:41
1

@HBMCS: well groups are not the permissions, but a group can have zero, one or more permissions. So yes, you can for example use groups over defining a `Role` model I think. Django's admin pages also normally have pages to edit the permissions. Furthemore there are decorators for permission checks. – Willem Van Onsem Jun 01 '20 at 19:43

Check for string in queryset within a Django template

1 Answers1