ModelAdmin should allow specifying Changelist class to further modify Changelist behavior

[anonymous]

I've been poking around the Django source as I want to add a column to the changelist view. Specifically, this column is a consolidation of a ManyToMany relationship. I'll use it as an example here.

In options.py, class ModelAdmin defines a function that instantiates a Changelist:

class ModelAdmin(BaseModelAdmin):
    def __init__(self, model, admin_site):
        self.model = model
        self.opts = model._meta
        self.admin_site = admin_site
        #more code

    #more code, more functions

    def changelist_view(self, request, extra_context=None):
        "The 'change list' admin view for this model."
        #more code here
        from django.contrib.admin.views.main import ChangeList, ERROR_FLAG
        #more code here
        try:
            cl = ChangeList(request, self.model, self.list_display, self.list_display_links, self.list_filter,
                     self.date_hierarchy, self.search_fields, self.list_select_related, self.list_per_page, self)
        #more code here

I propose the class 'ChangeList' be easily overidable, like so:

from django.contrib.admin.views.main import ChangeList, ERROR_FLAG

    class ModelAdmin(BaseModelAdmin):
        changelist_class = ChangeList
        def __init__(self, model, admin_site):
            self.model = model
            self.opts = model._meta
            self.admin_site = admin_site
            self.changelist_class = changelist_class
            #more code
    def changelist_view(self, request, extra_context=None):
        "The 'change list' admin view for this model."
        #more code here
        from django.contrib.admin.views.main import ChangeList, ERROR_FLAG
        #more code here
        try:
            cl = self.changelist_class(request, self.model, self.list_display, self.list_display_links, self.list_filter,
                     self.date_hierarchy, self.search_fields, self.list_select_related, self.list_per_page, self)
        #more code here

This would allow one to easily override some ChangeList methods from an admin.py file:

    from models import Object, ObjectRelationToWidget #ObjectRelationToWidget acts as the ManyToMany bridge table
    from django.contrib.admin.views.main import ChangeList

    class ObjectChangeList(ChangeList):
	    def get_results(self, request):

                r = ObjectRelationToWidget.objects.all().select_related() #this puts all the Objects and Widgets into the queryset cache
                results = []
                for obj in r:
                    r.object._v_local = {}
                    r.object._v_local['widget_name'] = r.widget.name
                    r.object.widget_name = lambda x: return x._v_local['widget_name']
                    results.append(r.object)

 	        self.result_count = len(results)
 	        self.full_result_count = len(results)
 	        self.result_list = results



     class ObjectAdmin(admin.ModelAdmin):
        changelist_class = ObjectChangeList
        list_display = ["object_name", "widget_name"]

Are there any thoughts on this suggestion? It is simple to add as a feature, but I suppose the usefulness may be seen as somewhat dubious. Suggestions for 'doing this better' (putting a related ManyToMany field in the admin changelist) would be appreciated, also.

[David Larlet]

I second this request, this is useful and I ran into similar issue (copy/paste the whole changelist_view function just to change the ChangeList call).

[David Larlet]

First iteration, review welcome

[David Larlet]

It seems that more tests are required in admin_views. I'll work on that part.

[David Larlet]

More tests, against r9728

[David Larlet]

admin_views' tests added.

[David Larlet]

New patch against r10069 (another bug resolution was conflictual with tests), nothing has changed

[David Larlet]

Just an update against r10087

[David Larlet]

Update against r10123 with feature freeze it will be more simple to maintain now

[David Larlet]

Update against r10680

[dc]

Maybe use 'changelist' instead of 'changelist_class'? Because currently admin has attribute 'form' (not 'form_class').

[David Larlet]

To me it looks more explicit to use the _class suffix when it's a class and not an instance. But I agree that historically configuration doesn't specify it's a class...

[Luke Plant]

One comment - the type checking for a subclass of ChangeList seems to be pointless and un-pythonic (duck-typing means you allow any object that has the right interface). Is there a good reason for it that I'm missing?

[floguy]

My version

[floguy]

I've approached this in a slightly different way. My way involves mimicking the way some of the other methods on the ModelAdmin class works (get_form, etc) by implementing a method to provide the class. This way is slightly more flexible due to the availability of more information (like everything from the request). I hope this patch makes it in, because right now trying to just slightly change behavior involves a whole lot of copy/paste.

I understand one concern with this is that it could make ChangeList a more public API, but it's still really not. For example, it's still not documented. But it does give greater flexibility at a per-request level, and that's what I'm after.

[David Larlet]

@lukeplant: This is un-pythonic but that's the way it's done in admin.validation.validate to check others attrs. Anyway, floguy's solution solve the problem.

@floguy: I agree that it can be very interesting to get the request object in this case and I prefer your approach (see luke's comment).

@jezdez: thanks for taking this :)

[Jannis Leidel]

(In [11910]) Fixed #9749 - Added hook to ModelAdmin for specifying custom ChangeLists. Thanks to David Larlet and Eric Florenzano.

[Jacob]

Milestone 1.2 deleted