Merge pull request #56 from ral-facilities/41_add_ability_to_get_dist…

…inct_values

Add ability to get distinct values

common/database_helpers.py

@@ -55,6 +55,7 @@ class ReadQuery(Query):
     def __init__(self, table):
         super().__init__(table)
         self.include_related_entities = False
+        self.is_distinct_fields_query = False
 
     def commit_changes(self):
         log.info("Closing DB session")
@@ -124,13 +125,18 @@ def execute_query(self):
 
 
 class QueryFilter(ABC):
+    @property
+    @abstractmethod
+    def precedence(self):
+        pass
+
     @abstractmethod
     def apply_filter(self, query):
         pass
 
 
 class WhereFilter(QueryFilter):
-    precedence = 0
+    precedence = 1
 
     def __init__(self, field, value, operation):
         self.field = field
@@ -151,8 +157,23 @@ def apply_filter(self, query):
             raise BadFilterError(f" Bad operation given to where filter. operation: {self.operation}")
 
 
+class DistinctFieldFilter(QueryFilter):
+    precedence = 0
+
+    def __init__(self, fields):
+        self.fields = fields if type(fields) is list else [fields]  # This allows single string distinct filters
+
+    def apply_filter(self, query):
+        query.is_distinct_fields_query = True
+        try:
+            self.fields = [getattr(query.table, field) for field in self.fields]
+        except AttributeError:
+            raise BadFilterError("Bad field requested")
+        query.base_query = query.session.query(*self.fields).distinct()
+
+
 class OrderFilter(QueryFilter):
-    precedence = 1
+    precedence = 2
 
     def __init__(self, field, direction):
         self.field = field
@@ -168,7 +189,7 @@ def apply_filter(self, query):
 
 
 class SkipFilter(QueryFilter):
-    precedence = 2
+    precedence = 3
 
     def __init__(self, skip_value):
         self.skip_value = skip_value
@@ -178,7 +199,7 @@ def apply_filter(self, query):
 
 
 class LimitFilter(QueryFilter):
-    precedence = 3
+    precedence = 4
 
     def __init__(self, limit_value):
         self.limit_value = limit_value
@@ -188,7 +209,7 @@ def apply_filter(self, query):
 
 
 class IncludeFilter(QueryFilter):
-    precedence = 4
+    precedence = 5
 
     def __init__(self, included_filters):
         self.included_filters = included_filters
@@ -221,6 +242,8 @@ def get_query_filter(filter):
             return LimitFilter(filter["limit"])
         elif filter_name == "include":
             return IncludeFilter(filter)
+        elif filter_name == "distinct":
+            return DistinctFieldFilter(filter["distinct"])
         else:
             raise BadFilterError(f" Bad filter: {filter}")
 
@@ -330,16 +353,43 @@ def get_filtered_read_query_results(filter_handler, filters, query):
                 filter_handler.add_filter(QueryFilterFactory.get_query_filter(query_filter))
         filter_handler.apply_filters(query)
         results = query.get_all_results()
+        if query.is_distinct_fields_query:
+            return _get_distinct_fields_as_dicts(results)
         if query.include_related_entities:
-            for query_filter in filters:
-                if list(query_filter)[0].lower() == "include":
-                    return list(map(lambda x: x.to_nested_dict(query_filter["include"]), results))
+            return _get_results_with_include(filters, results)
         return list(map(lambda x: x.to_dict(), results))
 
     finally:
         query.session.close()
 
 
+def _get_results_with_include(filters, results):
+    """
+    Given a list of entities and a list of filters, use the include filter to nest the included entities requested in
+    the include filter given
+    :param filters: The list of filters
+    :param results: The list of entities
+    :return: A list of nested dictionaries representing the entity results
+    """
+    for query_filter in filters:
+        if list(query_filter)[0].lower() == "include":
+            return [x.to_nested_dict(query_filter["include"]) for x in results]
+
+
+def _get_distinct_fields_as_dicts(results):
+    """
+    Given a list of column results return a list of dictionaries where each column name is the key and the column value
+    is the dictionary key value
+    :param results: A list of sql alchemy result objects
+    :return: A list of dictionary representations of the sqlalchemy result objects
+    """
+    dictionaries = []
+    for result in results:
+        dictionary = {k: getattr(result, k) for k in result.keys()}
+        dictionaries.append(dictionary)
+    return dictionaries
+
+
 def get_rows_by_filter(table, filters):
     """
     Given a list of filters supplied in json format, returns entities that match the filters from the given table
@@ -465,7 +515,7 @@ class InstrumentFacilityCyclesQuery(ReadQuery):
     def __init__(self, instrument_id):
         super().__init__(FACILITYCYCLE)
         investigationInstrument = aliased(INSTRUMENT)
-        self.base_query = self.base_query\
+        self.base_query = self.base_query \
             .join(FACILITYCYCLE.FACILITY) \
             .join(FACILITY.INSTRUMENT) \
             .join(FACILITY.INVESTIGATION) \
@@ -504,7 +554,7 @@ class InstrumentFacilityCycleInvestigationsQuery(ReadQuery):
     def __init__(self, instrument_id, facility_cycle_id):
         super().__init__(INVESTIGATION)
         investigationInstrument = aliased(INSTRUMENT)
-        self.base_query = self.base_query\
+        self.base_query = self.base_query \
             .join(INVESTIGATION.FACILITY) \
             .join(FACILITY.FACILITYCYCLE) \
             .join(FACILITY.INSTRUMENT) \