Merge pull request #35 from ral-facilities/30_use_order_of_operations

Use order of operations for filtering

common/database_helpers.py

@@ -16,7 +16,6 @@ def __init__(self, table):
         self.session = session_manager.get_icat_db_session()
         self.table = table
         self.base_query = self.session.query(table)
-        self.is_limited = False
 
     @abstractmethod
     def execute_query(self):
@@ -123,6 +122,8 @@ def apply_filter(self, query):
 
 
 class WhereFilter(QueryFilter):
+    precedence = 0
+
     def __init__(self, field, value):
         self.field = field
         self.value = value
@@ -132,13 +133,13 @@ def apply_filter(self, query):
 
 
 class OrderFilter(QueryFilter):
+    precedence = 1
+
     def __init__(self, field, direction):
         self.field = field
         self.direction = direction
 
     def apply_filter(self, query):
-        if query.is_limited:
-            query.base_query = query.base_query.from_self()
         if self.direction.upper() == "ASC":
             query.base_query = query.base_query.order_by(asc(self.field.upper()))
         elif self.direction.upper() == "DESC":
@@ -148,6 +149,8 @@ def apply_filter(self, query):
 
 
 class SkipFilter(QueryFilter):
+    precedence = 2
+
     def __init__(self, skip_value):
         self.skip_value = skip_value
 
@@ -156,15 +159,18 @@ def apply_filter(self, query):
 
 
 class LimitFilter(QueryFilter):
+    precedence = 3
+
     def __init__(self, limit_value):
         self.limit_value = limit_value
 
     def apply_filter(self, query):
         query.base_query = query.base_query.limit(self.limit_value)
-        query.is_limited = True
 
 
 class IncludeFilter(QueryFilter):
+    precedence = 4
+
     def __init__(self, included_filters):
         self.included_filters = included_filters
 
@@ -195,6 +201,32 @@ def get_query_filter(filter):
             raise BadFilterError(f" Bad filter: {filter}")
 
 
+class FilterOrderHandler(object):
+    """
+    The FilterOrderHandler takes in filters, sorts them according to the order of operations, then applies them.
+    """
+    def __init__(self):
+        self.filters = []
+
+    def add_filter(self, filter):
+        self.filters.append(filter)
+
+    def sort_filters(self):
+        """
+        Sorts the filters according to the order of operations
+        """
+        self.filters.sort(key=lambda x: x.precedence)
+
+    def apply_filters(self, query):
+        """
+        Given a query apply the filters the handler has in the correct order.
+        :param query: The query to have filters applied to
+        """
+        self.sort_filters()
+        for filter in self.filters:
+            filter.apply_filter(query)
+
+
 def insert_row_into_table(table, row):
     """
     Insert the given row into its table
@@ -264,12 +296,14 @@ def get_rows_by_filter(table, filters):
     :return: A list of the rows returned in dictionary form
     """
     query = ReadQuery(table)
+    filter_handler = FilterOrderHandler()
     try:
         for query_filter in filters:
             if len(query_filter) == 0:
                 pass
             else:
-                QueryFilterFactory.get_query_filter(query_filter).apply_filter(query)
+                filter_handler.add_filter(QueryFilterFactory.get_query_filter(query_filter))
+        filter_handler.apply_filters(query)
         results = query.get_all_results()
         if query.include_related_entities:
             for query_filter in filters:
@@ -301,11 +335,13 @@ def get_filtered_row_count(table, filters):
 
     log.info(f" getting count for {table.__tablename__}")
     count_query = CountQuery(table)
-    for filter in filters:
-        if len(filter) == 0:
+    filter_handler = FilterOrderHandler()
+    for query_filter in filters:
+        if len(query_filter) == 0:
             pass
         else:
-            QueryFilterFactory.get_query_filter(filter).apply_filter(count_query)
+            filter_handler.add_filter(QueryFilterFactory.get_query_filter(query_filter))
+    filter_handler.apply_filters(count_query)
     return count_query.get_count()