Add value transformation logic

README.md

@@ -17,7 +17,7 @@ installed using python-pip like `pip install drf-url-filters`.
 
 2. Add `filters` in INSTALLED_APPS of settings.py file of django project.
 
-**How it works?**
+**How it works**
 
 1. Your View or ModelViewSet should inherit `FiltersMixin` from
 `filters.mixins.FiltersMixin`.
@@ -26,6 +26,11 @@ installed using python-pip like `pip install drf-url-filters`.
 have a dict mapping `filter_mappings` which converts incoming query parameters
 to query you want to make on the column name on the queryset.
 
+3. Optionally, to perform any preprocessing on the incoming values for
+query params, add another dict `filter_value_transformations` which maps
+incoming query parameters to functions that should be applied to the values
+corresponding to them. The resultant value is used in the final filtering.
+
 # validations.py
 
 ```python
@@ -46,6 +51,7 @@ players_query_schema = base_query_param_schema.extend(
         "team_id": CSVofIntegers(),  # /?team_id=1,2,3
         "install_ts": DatetimeWithTZ(),
         "update_ts": DatetimeWithTZ(),
+        "taller_than": IntegerLike(),
     }
 )
 ```
@@ -88,6 +94,11 @@ class PlayersViewSet(FiltersMixin, viewsets.ModelViewSet):
         'update_ts': 'update_ts',
         'update_ts__gte': 'update_ts__gte',
         'update_ts__lte': 'update_ts__lte',
+        'taller_than': 'height__gte',
+    }
+
+    field_value_transformations = {
+        'taller_than': lambda val: val / 30.48  # cm to ft
     }
 
     # add validation on filters

docs/README.md

@@ -0,0 +1 @@
+../README.md

filters/mixins.py

@@ -26,6 +26,7 @@ def __get_queryset_filters(self, query_params, *args, **kwargs):
 
         if getattr(self, 'filter_mappings', None) and query_params:
             filter_mappings = self.filter_mappings
+            value_transformations = getattr(self, 'filter_value_transformations', {})
 
             try:
                 # check and raise 400_BAD_REQUEST for invalid query params
@@ -46,15 +47,16 @@ def __get_queryset_filters(self, query_params, *args, **kwargs):
                 # [1] ~ sign is used to exclude a filter.
                 is_exclude = '~' in query
                 if query in self.filter_mappings and value:
-                    query = filter_mappings[query]
+                    query_filter = filter_mappings[query]
+                    transform_value = value_transformations.get(query, lambda val: val)
+                    transformed_value = transform_value(value)
                     # [2] multiple options is filter values will execute as `IN` query
-                    if isinstance(value, list):
-                        query += '__in'
-                    if value:
-                        if is_exclude:
-                            excludes.append((query, value))
-                        else:
-                            filters.append((query, value))
+                    if isinstance(value, list) and not query_filter.endswith('__in'):
+                        query_filter += '__in'
+                    if is_exclude:
+                        excludes.append((query_filter, transformed_value))
+                    else:
+                        filters.append((query_filter, transformed_value))
 
         return dict(filters), dict(excludes)