dokterbob · February 15, 2011 20:00 · Feb 15, 2011 · Feb 15, 2011
diff --git a/snippet.sc → admin.py b/snippet.sc → admin.py
diff --git a/snippet.sc b/snippet.sc
@@ -0,0 +1,65 @@
+class LimitedAdminInlineMixin(object):
+    """
+    InlineAdmin mixin limiting the selection of related items according to
+    criteria which can depend on the current parent object being edited.
+
+    A typical use case would be selecting a subset of related items from
+    other inlines, ie. images, to have some relation to other inlines.
+
+    Use as follows::
+
+        class MyInline(LimitedAdminInlineMixin, admin.TabularInline):
+            def get_filters(self, obj):
+                return (('<field_name>', dict(<filters>)),)
+
+    """
+
+    @staticmethod
+    def limit_inline_choices(formset, field, empty=False, **filters):
+        """
+        This function fetches the queryset with available choices for a given
+        `field` and filters it based on the criteria specified in filters,
+        unless `empty=True`. In this case, no choices will be made available.
+        """
+        assert formset.form.base_fields.has_key(field)
+
+        qs = formset.form.base_fields[field].queryset
+        if empty:
+            logger.debug('Limiting the queryset to none')
+            formset.form.base_fields[field].queryset = qs.none()
+        else:
+            qs = qs.filter(**filters)
+            logger.debug('Limiting queryset for formset to: %s', qs)
+
+            formset.form.base_fields[field].queryset = qs
+
+    def get_formset(self, request, obj=None, **kwargs):
+        """
+        Make sure we can only select variations that relate to the current
+        item.
+        """
+        formset = \
+            super(LimitedAdminInlineMixin, self).get_formset(request,
+                                                             obj,
+                                                             **kwargs)
+
+        for (field, filters) in self.get_filters(obj):
+            if obj:
+                self.limit_inline_choices(formset, field, **filters)
+            else:
+                self.limit_inline_choices(formset, field, empty=True)
+
+        return formset
+
+    def get_filters(self, obj):
+        """
+        Return filters for the specified fields. Filters should be in the
+        following format::
+
+            (('field_name', {'categories': obj}), ...)
+
+        For this to work, we should either override `get_filters` in a
+        subclass or define a `filters` property with the same syntax as this
+        one.
+        """
+        return getattr(self, 'filters', ())
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