#145: Move filter-specific functions to FilterOrderHandler

- This will help clean up common.icat.helpers and move filter-specific functions to the relevant file
- This commit also adds a function that calls other functions in its class to reduce code duplication
- This is a 'leave the code in a better state than you found it' kind of commit

common/filter_order_handler.py

@@ -1,3 +1,10 @@
+from common.icat.filters import (
+    PythonICATLimitFilter,
+    PythonICATSkipFilter,
+    PythonICATOrderFilter,
+)
+
+
 class FilterOrderHandler(object):
     """
     The FilterOrderHandler takes in filters, sorts them according to the order of
@@ -32,3 +39,65 @@ def apply_filters(self, query):
 
         for filter in self.filters:
             filter.apply_filter(query)
+
+    def merge_python_icat_limit_skip_filters(self):
+        """
+        When there are both limit and skip filters in a request, merge them into the
+        limit filter and remove the skip filter from the instance
+        """
+
+        if any(
+            isinstance(icat_filter, PythonICATSkipFilter)
+            for icat_filter in self.filters
+        ) and any(
+            isinstance(icat_filter, PythonICATLimitFilter)
+            for icat_filter in self.filters
+        ):
+            # Merge skip and limit filter into a single limit filter
+            for icat_filter in self.filters:
+                if isinstance(icat_filter, PythonICATSkipFilter):
+                    skip_filter = icat_filter
+                    request_skip_value = icat_filter.skip_value
+
+                if isinstance(icat_filter, PythonICATLimitFilter):
+                    limit_filter = icat_filter
+
+            if skip_filter and limit_filter:
+                log.info("Merging skip filter with limit filter")
+                limit_filter.skip_value = skip_filter.skip_value
+                log.info("Removing skip filter from list of filters")
+                self.remove_filter(skip_filter)
+                log.debug("Filters: %s", self.filters)
+
+    def clear_python_icat_order_filters(self):
+        """
+        Checks if any order filters have been added to the request and resets the
+        variable used to manage which attribute(s) to use for sorting results.
+        
+        A reset is required because Python ICAT overwrites (as opposed to appending to
+        it) the query's order list every time one is added to the query.
+        """
+
+        if any(
+            isinstance(icat_filter, PythonICATOrderFilter)
+            for icat_filter in self.filters
+        ):
+            PythonICATOrderFilter.result_order = []
+
+    def manage_icat_filters(self, filters, query):
+        """
+        Utility function to call other functions in this class, used to manage filters
+        when using the Python ICAT backend. These steps are the same with the different
+        types of requests that utilise filters, therefore this function helps to reduce
+        code duplication
+
+        :param filters: The list of filters that will be applied to the query
+        :type filters: List of specific implementations :class:`QueryFilter`
+        :param query: ICAT query which will fetch the data at a later stage
+        :type query: :class:`icat.query.Query`
+        """
+
+        self.add_filters(filters)
+        self.merge_python_icat_limit_skip_filters()
+        self.clear_python_icat_order_filters()
+        self.apply_filters(query)

common/icat/helpers.py

@@ -24,13 +24,7 @@
 from common.filter_order_handler import FilterOrderHandler
 from common.date_handler import DateHandler
 from common.constants import Constants
-from common.icat.filters import (
-    PythonICATLimitFilter,
-    PythonICATWhereFilter,
-    PythonICATSkipFilter,
-    PythonICATOrderFilter,
-)
-
+from common.icat.filters import PythonICATLimitFilter, PythonICATWhereFilter
 
 log = logging.getLogger()
 
@@ -621,10 +615,7 @@ def get_entity_with_filters(client, table_name, filters):
     query = icat_query(client, selected_entity_name)
 
     filter_handler = FilterOrderHandler()
-    filter_handler.add_filters(filters)
-    merge_limit_skip_filters(filter_handler)
-    clear_order_filters(filter_handler.filters)
-    filter_handler.apply_filters(query.query)
+    filter_handler.manage_icat_filters(filters, query.query)
 
     data = query.execute_query(client, True)
 
@@ -634,53 +625,6 @@ def get_entity_with_filters(client, table_name, filters):
         return data
 
 
-def merge_limit_skip_filters(filter_handler):
-    """
-    When there are both limit and skip filters in a request, merge them into the limit
-    filter and remove the skip filter from `filter_handler`
-
-    :param filter_handler: The filter handler to apply the filters
-    :param filters: The filters to be applied
-    """
-
-    if any(
-        isinstance(filter, PythonICATSkipFilter) for filter in filter_handler.filters
-    ) and any(
-        isinstance(filter, PythonICATLimitFilter) for filter in filter_handler.filters
-    ):
-        # Merge skip and limit filter into a single limit filter
-        for filter in filter_handler.filters:
-            if isinstance(filter, PythonICATSkipFilter):
-                skip_filter = filter
-                request_skip_value = filter.skip_value
-
-            if isinstance(filter, PythonICATLimitFilter):
-                limit_filter = filter
-
-        if skip_filter and limit_filter:
-            log.info("Merging skip filter with limit filter")
-            limit_filter.skip_value = skip_filter.skip_value
-            log.info("Removing skip filter from list of filters")
-            filter_handler.remove_filter(skip_filter)
-            log.debug("Filters: %s", filter_handler.filters)
-
-
-def clear_order_filters(filters):
-    """
-    Checks if any order filters have been added to the request and resets the variable
-    used to manage which attribute(s) to use for sorting results.
-    
-    A reset is required because Python ICAT overwrites (as opposed to appending to it)
-    the query's order list every time one is added to the query.
-
-    :param filters: The list of filters to be applied to the request
-    :type filters: List of specific implementations :class:`QueryFilter`
-    """
-
-    if any(isinstance(filter, PythonICATOrderFilter) for filter in filters):
-        PythonICATOrderFilter.result_order = []
-
-
 def get_count_with_filters(client, table_name, filters):
     """
     Get the number of results of a given entity, based on the filters provided in the
@@ -705,10 +649,7 @@ def get_count_with_filters(client, table_name, filters):
     query = icat_query(client, selected_entity_name, aggregate="COUNT")
 
     filter_handler = FilterOrderHandler()
-    filter_handler.add_filters(filters)
-    merge_limit_skip_filters(filter_handler)
-    clear_order_filters(filter_handler.filters)
-    filter_handler.apply_filters(query.query)
+    filter_handler.manage_icat_filters(filters, query.query)
 
     data = query.execute_query(client, True)