Location header improvements(#1475)

* Create location header only on primary key columns, closes https://github.com/PostgREST/postgrest/issues/1461

* Return location header when pk columns not selected, fixes https://github.com/PostgREST/postgrest/issues/1162

src/PostgREST/DbRequestBuilder.hs

@@ -316,7 +316,7 @@ mutateRequest schema tName apiRequest cols pkCols readReq = mapLeft errorRespons
     returnings =
       if iPreferRepresentation apiRequest == None
         then []
-        else returningCols readReq
+        else returningCols readReq pkCols
     filters = map snd <$> mapM pRequestFilter mutateFilters
     logic = map snd <$> mapM pRequestLogicTree logicFilters
     combinedLogic = foldr addFilterToLogicForest <$> logic <*> filters
@@ -324,8 +324,11 @@ mutateRequest schema tName apiRequest cols pkCols readReq = mapLeft errorRespons
     (mutateFilters, logicFilters) = join (***) onlyRoot (iFilters apiRequest, iLogic apiRequest)
     onlyRoot = filter (not . ( "." `isInfixOf` ) . fst)
 
-returningCols :: ReadRequest -> [FieldName]
-returningCols rr@(Node _ forest) = returnings
+returningCols :: ReadRequest -> [FieldName] -> [FieldName]
+returningCols rr@(Node _ forest) pkCols
+  -- if * is part of the select, we must not add pk or fk columns manually - otherwise those would be selected and output twice
+  | "*" `elem` fldNames = ["*"]
+  | otherwise           = returnings
   where
     fldNames = fstFieldNames rr
     -- Without fkCols, when a mutateRequest to /projects?select=name,clients(name) occurs, the RETURNING SQL part would be
@@ -343,7 +346,8 @@ returningCols rr@(Node _ forest) = returnings
     -- However if the "client_id" is present, e.g. mutateRequest to /projects?select=client_id,name,clients(name)
     -- we would get `RETURNING client_id, name, client_id` and then we would produce the "column reference \"client_id\" is ambiguous"
     -- error from PostgreSQL. So we deduplicate with Set:
-    returnings = S.toList . S.fromList $ fldNames ++ (colName <$> fkCols)
+    -- We are adding the primary key columns as well to make sure, that a proper location header can always be built for INSERT/POST
+    returnings = S.toList . S.fromList $ fldNames ++ (colName <$> fkCols) ++ pkCols
 
 -- Traditional filters(e.g. id=eq.1) are added as root nodes of the LogicTree
 -- they are later concatenated with AND in the QueryBuilder