ModelAdmin should allow for overriding of ForeignKey/ManyToMany options

the patch

Details : http://groups.google.com/group/django-developers/browse_thread/thread/1695343f1e5cdc36/f4918ceac3a2f246#f4918ceac3a2f246

I like the idea, but the implementation is a bit brittle. What about adding method hooks on ModelAdmin that would allow you to specify the options for a given ForeignKey field? These methods could get passed the request object, so you could do per-user options. Something like this:

# Model

class Book(models.Model):
    title = models.CharField(maxlength=100)
    author = models.ForeignKey(Author)

# Admin

class BookAdmin(ModelAdmin):
    def dynamic_author_choices(self, request, book):
        # Default implementation:
        # return book.author_set.all()
        return book.author_set.filter(use_in_admin=True)

If dynamic_field_choices() is automatically called for every field when admin is displayed, that would be great, but should also work for ManyToManyField?.

new patch (cleaner ?)

Okay, here is a new patch that I hope cleaner.

It works almost like Adrian suggested it :

# Model

class Book(models.Model):
    title = models.CharField(maxlength=100)
    author = models.ForeignKey(Author)

# Admin

class BookAdmin(ModelAdmin):
    def dynamic_author_choices(self, request, model):
        # Default implementation:
        # return book.author_set.all()
        return model.objects.filter(use_in_admin=True)

And also allows:

class BookAdmin(ModelAdmin):
    def dynamic_author_choices(self, request, model):
        if request.user.is_superuser:
            return model.objects.all()
        return model.objects.filter(use_in_admin=True)            

oops, fixed a little error

security fix : the choice of an item not in the list of choices must fail

I am +1 for this patch. This is really a useful addition.

I attached an updated version of patch. It now works with revision: 6426.

A little change I did to the patch is removal of all occurences of:

defaults = {'form_class': forms.ModelChoiceField} 
#To prevent an useless query
if not 'queryset' in kwargs: 
   defaults['queryset'] = self.rel.to._default_manager.all()

in favour of original code:

defaults = {'form_class': forms.ModelChoiceField, 'queryset': self.rel.to._default_manager.all()} 

The reason is that QuerySets are lazy so there is no "useless query".

Patch updated to work with version 6426

I replaced the previous version of the patch, because it had a small bug. I did simple replacement in line 203 of models.py (s/value/val/)

New function so it shouldn't block newforms-admin merge. Also it needs docs and tests, I think.

It doesn't block the merge since it is a newforms-admin patch.

But I am not going to write doc and tests since I haven't had any feedback about this and I have no idea if it has a chance to be accepted! If someone said it could be accepted, I would do it, sure.

Replying to Baptiste:

But I am not going to write doc and tests since I haven't had any feedback about this and I have no idea if it has a chance to be accepted! If someone said it could be accepted, I would do it, sure.

Triage stage is Accepted, and you've updated the patch to be in line with Adrian's suggestion, so I was thinking it had been accepted. I believe a complete package is more likely than just a code patch to get the review needed to move on to ready for checkin.

Replying to Baptiste:

But I am not going to write doc and tests since I haven't had any feedback about this and I have no idea if it has a chance to be accepted! If someone said it could be accepted, I would do it, sure.

It should be accepted. Enough? ;) Hey! This patch is very important to me. It would be great to have it merged with the trunk!

Updated to revision 8151

Replying to Baptiste <baptiste.goupil@gmail.com>:

See discussion in comments.

I think I have upgraded the patch to work with latest SVN copy. First time looking into the code!

Would greatly appreciate it if this patch was included in 1.0 as it's an incredibly handy feature.

Replying to mikeblake:

Would greatly appreciate it if this patch was included in 1.0 as it's an incredibly handy feature.

It was accepted by Adrian and seems to have multiple people interested in it, however it's got no docs nor tests. That's probably preventing it from moving along in the process.

tentative feature documentation

New patch (sorry, fisrt try) , forget/delete the preceding one if possible

First proposal for a documentation. Forget the first patch, totally wrong.

updated, works with revision 8502

sorry, forgot to change extension

Looks like Mr Anonymous is having a bit of fun here...

I'ld like to show in model A list_filter model B fields that have a ForeignKey to model A. I've applied dynamic_related_3987.2.diff to django svn trunk. I've add a method get_b() to the A admin class ("class AAdmin(admin.ModelAdmin?):") that returns a.b_set.all(), but I don't know how I've to include it in list_filter. I've put "list_filter = (...,'get_b')" but get the error:

Error while importing URLconf 'myapp.urls': `AAdmin.list_filter[9]` refers to field `get_b` that is missing from model `A`.

What should be solve the error?

Thanks in advance.

Updated patch to rev 9014. This will work with 1.0 also.

There is a serious problem with this patch. It changes the formfield_for_dbfield method of ModelAdmin?, requiring a request object to passed in as a positional argument. This method is not in the docs, but it is commonly overridden, and represents a significant change to the API for the Admin.

There is a way to do what this patch does on 1.0, without any patching:

class SiteAdmin(ModelAdmin):
    def __call__(self, request, url):
        #Add in the request object, so that it may be referenced
        #later in the formfield_for_dbfield function.
        self.request = request
        return super(SiteAdmin, self).__call__(request, url)
    
    def get_form(self, request, obj=None):
        form = super(SiteAdmin, self).get_form(request, obj)
        #print form
        return form
            
    def formfield_for_dbfield(self, db_field, **kwargs):
        field = super(SiteAdmin, self).formfield_for_dbfield(db_field, **kwargs) # Get the default field
        if db_field.name == 'home_page': 
            #Add the null object
            my_choices = [('', '---------')]
            #Grab the current site id from the URL.
            my_choices.extend(Page.objects.filter(site=self.request.META['PATH_INFO'].split('/')[-2]).values_list('id','name'))
            print my_choices
            field.choices = my_choices
        return field

The trick is the override of _ _call_ _, adding the request object as an attribute of the instance. Once you have this, you can do pretty much anything you need in the formfield_for_dbfield override. Granted, this is not very elegant. But it works in 1.0, and our users are already accustomed to overriding formfield_for_dbfield to make custom form tweaks.

Sorry. Had some superfluous code in that example. Updated version for reference:

class SiteAdmin(ModelAdmin):
    def __call__(self, request, url):
        #Add in the request object, so that it may be referenced
        #later in the formfield_for_dbfield function.
        self.request = request
        return super(SiteAdmin, self).__call__(request, url)
    
    def formfield_for_dbfield(self, db_field, **kwargs):
        field = super(SiteAdmin, self).formfield_for_dbfield(db_field, **kwargs) # Get the default field
        if db_field.name == 'home_page': 
            #Add the null object
            my_choices = [('', '---------')]
            #Grab the current site id from the URL.
            my_choices.extend(Page.objects.filter(site=self.request.META['PATH_INFO'].split('/')[-2]).values_list('id','name'))
            print my_choices
            field.choices = my_choices
        return field

(In [9760]) Cleaned up and refactored ModelAdmin.formfield_for_dbfield:

• The new method uses an admin configuration option (formfield_overrides); this makes custom admin widgets especially easy.
• Refactored what was left of formfield_for_dbfield into a handful of smaller methods so that it's easier to hook in and return custom fields where needed.
• These formfield_for_* methods now pass around request so that you can easily modify fields based on request (as in #3987).

Fixes #8306, #3987, #9148.

Thanks to James Bennet for the original patch; Alex Gaynor and Brian Rosner also contributed.