#150: Move QueryFilterFactory to its own file

- It used to be in the database helpers file, but this class is used across both backends
- The imports have been moved inside the staticmethod because the Flask TEST_BACKEND config option won't have been set by the time QueryFilterFactory has been imported, so the imports which decide which set of filters to import must be put in some code.

datagateway_api/common/database/helpers.py

@@ -202,42 +202,6 @@ def execute_query(self):
         self.commit_changes()
 
 
-class QueryFilterFactory(object):
-    @staticmethod
-    def get_query_filter(request_filter):
-        """
-        Given a filter return a matching Query filter object
-
-        This factory is not in common.filters so the created filter can be for the
-        correct backend. Moving the factory into that file would mean the filters would
-        be based off the abstract classes (because they're in the same file) which won't
-        enable filters to be unique to the backend
-
-        :param request_filter: dict - The filter to create the QueryFilter for
-        :return: The QueryFilter object created
-        """
-        filter_name = list(request_filter)[0].lower()
-        if filter_name == "where":
-            field = list(request_filter[filter_name].keys())[0]
-            operation = list(request_filter[filter_name][field].keys())[0]
-            value = request_filter[filter_name][field][operation]
-            return WhereFilter(field, value, operation)
-        elif filter_name == "order":
-            field = request_filter["order"].split(" ")[0]
-            direction = request_filter["order"].split(" ")[1]
-            return OrderFilter(field, direction)
-        elif filter_name == "skip":
-            return SkipFilter(request_filter["skip"])
-        elif filter_name == "limit":
-            return LimitFilter(request_filter["limit"])
-        elif filter_name == "include":
-            return IncludeFilter(request_filter["include"])
-        elif filter_name == "distinct":
-            return DistinctFieldFilter(request_filter["distinct"])
-        else:
-            raise FilterError(f" Bad filter: {request_filter}")
-
-
 def insert_row_into_table(table, row):
     """
     Insert the given row into its table

datagateway_api/common/helpers.py

@@ -6,7 +6,7 @@
 from flask_restful import reqparse
 from sqlalchemy.exc import IntegrityError
 
-from datagateway_api.common.database.helpers import QueryFilterFactory
+from datagateway_api.common.query_filter import QueryFilterFactory
 from datagateway_api.common.exceptions import (
     ApiError,
     AuthenticationError,

datagateway_api/common/query_filter.py

@@ -0,0 +1,72 @@
+import logging
+
+from datagateway_api.common.config import config
+from datagateway_api.common.exceptions import (
+    ApiError,
+    FilterError,
+)
+
+log = logging.getLogger()
+
+
+class QueryFilterFactory(object):
+    @staticmethod
+    def get_query_filter(request_filter):
+        """
+        Given a filter return a matching Query filter object
+
+        This factory is not in common.filters so the created filter can be for the
+        correct backend. Moving the factory into that file would mean the filters would
+        be based off the abstract classes (because they're in the same file) which won't
+        enable filters to be unique to the backend
+
+        :param request_filter: dict - The filter to create the QueryFilter for
+        :return: The QueryFilter object created
+        """
+
+        backend_type = config.get_backend_type()
+        print(f"Backend inside staticmethod: {backend_type}")
+        if backend_type == "db":
+            from datagateway_api.common.database.filters import (
+                DatabaseDistinctFieldFilter as DistinctFieldFilter,
+                DatabaseIncludeFilter as IncludeFilter,
+                DatabaseLimitFilter as LimitFilter,
+                DatabaseOrderFilter as OrderFilter,
+                DatabaseSkipFilter as SkipFilter,
+                DatabaseWhereFilter as WhereFilter,
+            )
+        elif backend_type == "python_icat":
+            from datagateway_api.common.icat.filters import (
+                PythonICATDistinctFieldFilter as DistinctFieldFilter,
+                PythonICATIncludeFilter as IncludeFilter,
+                PythonICATLimitFilter as LimitFilter,
+                PythonICATOrderFilter as OrderFilter,
+                PythonICATSkipFilter as SkipFilter,
+                PythonICATWhereFilter as WhereFilter,
+            )
+        else:
+            raise ApiError(
+                "Cannot select which implementation of filters to import, check the"
+                " config file has a valid backend type",
+            )
+
+        filter_name = list(request_filter)[0].lower()
+        if filter_name == "where":
+            field = list(request_filter[filter_name].keys())[0]
+            operation = list(request_filter[filter_name][field].keys())[0]
+            value = request_filter[filter_name][field][operation]
+            return WhereFilter(field, value, operation)
+        elif filter_name == "order":
+            field = request_filter["order"].split(" ")[0]
+            direction = request_filter["order"].split(" ")[1]
+            return OrderFilter(field, direction)
+        elif filter_name == "skip":
+            return SkipFilter(request_filter["skip"])
+        elif filter_name == "limit":
+            return LimitFilter(request_filter["limit"])
+        elif filter_name == "include":
+            return IncludeFilter(request_filter["include"])
+        elif filter_name == "distinct":
+            return DistinctFieldFilter(request_filter["distinct"])
+        else:
+            raise FilterError(f" Bad filter: {request_filter}")