How to show different inlines depending of current object field value

Question

Given a model named MainModel and a RelatedModel, where the later has a ForeignKey field to MainModel:

class          


        

Answer 1

From peeking at contrib.admin.options.pyLooks like you could override ModelAdmin.get_formsets. Note that the admin site populates self.inline_instances at __init__, so you probably want to follow and not instantiate your inlines over and over. I'm not sure how expensive it is : )

def get_formsets(self, request, obj=None):
    if not obj:
        return [] # no inlines

    elif obj.type == True:
        return [MyInline1(self.model, self.admin_site).get_formset(request, obj)]

    elif obj.type == False:
        return [MyInline2(self.model, self.admin_site).get_formset(request, obj)]

    # again, not sure how expensive MyInline(self.model, self.admin_site) is. 
    # the admin does this once. You could instantiate them and store them on the 
    # admin class somewhere to reference instead.

The original admin get_formsets uses generators - you could too to more closely mimic the original:

def get_formsets(self, request, obj=None):
    for inline in self.inline_instances:
        yield inline.get_formset(request, obj)