✨Make EagerLoading mixin independent of DynamicFieldsMixin

- Introduce `RequestQueryParserMixin` used by both `DynamicFieldsMixiin` & `EagerLoadingMixin`, Closes #86
- Make query parameter name configurable through settings file, Closes #84

django_restql/mixins.py

@@ -4,7 +4,7 @@
     Serializer, ListSerializer,
     ValidationError
 )
-from django.db.models import Prefetch
+from django.conf import settings
 from django.db.models.fields.related import(
     ManyToOneRel, ManyToManyRel
 )
@@ -18,36 +18,26 @@
 )
 
 
-class DynamicFieldsMixin(object):
-    query_param_name = "query"
-
-    def __init__(self, *args, **kwargs):
-        # Don't pass 'query', 'fields' and 'exclude' kwargs to the superclass
-        self.query = kwargs.pop('query', None)  # Parsed query
-        self.allowed_fields = kwargs.pop('fields', None)
-        self.excluded_fields = kwargs.pop('exclude', None)
-        self.return_pk = kwargs.pop('return_pk', False)
-
-        is_field_kwarg_set = self.allowed_fields is not None
-        is_exclude_kwarg_set = self.excluded_fields is not None
-        msg = "May not set both `fields` and `exclude`"
-        assert not(is_field_kwarg_set and is_exclude_kwarg_set), msg
-
-        # Instantiate the superclass normally
-        super().__init__(*args, **kwargs)
-
-    def to_representation(self, instance):
-        if self.return_pk:
-            return instance.pk
-        return super().to_representation(instance)
+class RequestQueryParserMixin(object):
+    @staticmethod
+    def get_query_param_name():
+        DEFAULT_QUERY_PARAM_NAME = 'query'
+        query_param_name = getattr(
+            settings,
+            "QUERY_PARAM_NAME",
+            DEFAULT_QUERY_PARAM_NAME
+        )
+        return query_param_name
 
     @classmethod
     def has_query_param(cls, request):
-        return cls.query_param_name in request.query_params
+        query_param_name = cls.get_query_param_name()
+        return query_param_name in request.query_params
 
     @classmethod
     def get_raw_query(cls, request):
-        return request.query_params[cls.query_param_name]
+        query_param_name = cls.get_query_param_name()
+        return request.query_params[query_param_name]
 
     @classmethod
     def get_parsed_query_from_req(cls, request):
@@ -64,6 +54,28 @@ def get_parsed_query_from_req(cls, request):
             )
             raise ValidationError(msg) from None
 
+
+class DynamicFieldsMixin(RequestQueryParserMixin):
+    def __init__(self, *args, **kwargs):
+        # Don't pass 'query', 'fields' and 'exclude' kwargs to the superclass
+        self.query = kwargs.pop('query', None)  # Parsed query
+        self.allowed_fields = kwargs.pop('fields', None)
+        self.excluded_fields = kwargs.pop('exclude', None)
+        self.return_pk = kwargs.pop('return_pk', False)
+
+        is_field_kwarg_set = self.allowed_fields is not None
+        is_exclude_kwarg_set = self.excluded_fields is not None
+        msg = "May not set both `fields` and `exclude`"
+        assert not(is_field_kwarg_set and is_exclude_kwarg_set), msg
+
+        # Instantiate the superclass normally
+        super().__init__(*args, **kwargs)
+
+    def to_representation(self, instance):
+        if self.return_pk:
+            return instance.pk
+        return super().to_representation(instance)
+
     def get_allowed_fields(self):
         fields = super().fields
         if self.allowed_fields is not None:
@@ -268,20 +280,16 @@ def fields(self):
             return {}
 
 
-class EagerLoadingMixin(object):
+class EagerLoadingMixin(RequestQueryParserMixin):
     @property
     def parsed_query(self):
         """
         Gets parsed query for use in eager loading. 
         Defaults to the serializer parsed query assuming
         using django-restql DynamicsFieldMixin.
         """
-        if hasattr(self, "get_serializer_class"):
-            serializer_class = self.get_serializer_class()
-
-            if issubclass(serializer_class, DynamicFieldsMixin):
-                if serializer_class.has_query_param(self.request):
-                    return serializer_class.get_parsed_query_from_req(self.request)
+        if self.has_query_param(self.request):
+            return self.get_parsed_query_from_req(self.request)
 
         # Else include all fields
         query = {
@@ -391,7 +399,7 @@ def get_queryset(self):
             queryset = super().get_queryset()
             queryset = self.get_eager_queryset(queryset)
             return queryset
-            
+
 
 class NestedCreateMixin(object):
     """ Create Mixin """