Fix bug in many-many relation detection introduced but prev PR

src/PostgREST/DbStructure.hs

@@ -127,12 +127,14 @@ addParentRelations [] = []
 addParentRelations (rel@(Relation t c ft fc _ _ _ _):rels) = Relation ft fc t c Parent Nothing Nothing Nothing : rel : addParentRelations rels
 
 addManyToManyRelations :: [Relation] -> [Relation]
-addManyToManyRelations rels = rels ++ mapMaybe link2Relation links
+addManyToManyRelations rels = rels ++ addMirrorRelation (mapMaybe link2Relation links)
   where
     links = join $ map (combinations 2) $ filter (not . null) $ groupWith groupFn $ filter ( (==Child). relType) rels
     groupFn :: Relation -> Text
     groupFn (Relation{relTable=Table{tableSchema=s, tableName=t}}) = s<>"_"<>t
     combinations k ns = filter ((k==).length) (subsequences ns)
+    addMirrorRelation [] = []
+    addMirrorRelation (rel@(Relation t c ft fc _ lt lc1 lc2):rels') = Relation ft fc t c Many lt lc2 lc1 : rel : addMirrorRelation rels'
     link2Relation [
       Relation{relTable=lt, relColumns=lc1, relFTable=t,  relFColumns=c},
       Relation{             relColumns=lc2, relFTable=ft, relFColumns=fc}

src/PostgREST/QueryBuilder.hs

@@ -129,7 +129,6 @@ addRelations schema allRelations parentNode node@(Node readNode@(query, (name, _
       where
         rel = note ("no relation between " <> parentTable <> " and " <> name)
             $  findRelationByTable schema name parentTable
-           <|> findRelationByTable schema parentTable name
            <|> findRelationByColumn schema parentTable name
         addRel :: (ReadQuery, (NodeName, Maybe Relation)) -> Relation -> (ReadQuery, (NodeName, Maybe Relation))
         addRel (q, (n, _)) r = (q {from=fromRelation}, (n, Just r))

test/Feature/QuerySpec.hs

@@ -214,6 +214,11 @@ spec struct pool = around (withApp cfgDefault struct pool) $ do
       get "/tasks?select=id,users{id}" `shouldRespondWith`
         [str|[{"id":1,"users":[{"id":1},{"id":3}]},{"id":2,"users":[{"id":1}]},{"id":3,"users":[{"id":1}]},{"id":4,"users":[{"id":1}]},{"id":5,"users":[{"id":2},{"id":3}]},{"id":6,"users":[{"id":2}]},{"id":7,"users":[{"id":2}]},{"id":8,"users":[]}]|]
 
+
+    it "requesting many<->many relation reverse" $
+      get "/users?select=id,tasks{id}" `shouldRespondWith`
+        [str|[{"id":1,"tasks":[{"id":1},{"id":2},{"id":3},{"id":4}]},{"id":2,"tasks":[{"id":5},{"id":6},{"id":7}]},{"id":3,"tasks":[{"id":1},{"id":5}]}]|]
+
     it "requesting parents and children on views" $
       get "/projects_view?id=eq.1&select=id, name, clients{*}, tasks{id, name}" `shouldRespondWith`
         [str|[{"id":1,"name":"Windows 7","clients":{"id":1,"name":"Microsoft"},"tasks":[{"id":1,"name":"Design w7"},{"id":2,"name":"Code w7"}]}]|]