dependent fields

dependent fields.diff

diff --git a/django_select2/forms.py b/django_select2/forms.py
index f013bcc..f760e18 100644
--- a/django_select2/forms.py
+++ b/django_select2/forms.py
@@ -182,10 +182,15 @@ class HeavySelect2Mixin(object):
         Args:
             data_view (str): URL pattern name
             data_url (str): URL
+            dependent_fields (List[str]): List of dependent parent fields.
+                The value of the dependent field will be passed as to :func:`.filter_queryset`.
+                It can be used to further restrict the search results. For example, a city
+                widget could be dependent on a country.
 
         """
         self.data_view = kwargs.pop('data_view', None)
         self.data_url = kwargs.pop('data_url', None)
+        self.dependent_fields = kwargs.pop('dependent_fields', [])
         if not (self.data_view or self.data_url):
             raise ValueError('You must ether specify "data_view" or "data_url".')
         self.userGetValTextFuncName = kwargs.pop('userGetValTextFuncName', 'null')
@@ -209,6 +214,7 @@ class HeavySelect2Mixin(object):
         attrs.setdefault('data-ajax--cache', "true")
         attrs.setdefault('data-ajax--type', "GET")
         attrs.setdefault('data-minimum-input-length', 2)
+        attrs.setdefault('data-select2-dependent-fields', " ".join(self.dependent_fields))
 
         attrs['class'] += ' django-select2-heavy'
         return attrs
@@ -351,12 +357,13 @@ class ModelSelect2Mixin(object):
             'url': self.get_url(),
         })
 
-    def filter_queryset(self, term, queryset=None):
+    def filter_queryset(self, term, queryset=None, **kwargs):
         """
         Return QuerySet filtered by search_fields matching the passed term.
 
         Args:
             term (str): Search term
+            **kwargs: Dependent fields and their values.
 
         Returns:
             QuerySet: Filtered QuerySet
diff --git a/django_select2/views.py b/django_select2/views.py
index 71a12aa..cc99a6f 100644
--- a/django_select2/views.py
+++ b/django_select2/views.py
@@ -52,7 +52,11 @@ class AutoResponseView(BaseListView):
 
     def get_queryset(self):
         """Get QuerySet from cached widget."""
-        return self.widget.filter_queryset(self.term, self.queryset)
+        kwargs = {
+            field: self.request.GET.get(field, '')
+            for field in self.widget.dependent_fields
+        }
+        return self.widget.filter_queryset(self.term, self.queryset, **kwargs)
 
     def get_paginate_by(self, queryset):
         """Paginate response by size of widget's `max_results` parameter."""