Fix #1221, embedding when having a self join

src/PostgREST/DbRequestBuilder.hs

@@ -76,7 +76,7 @@ readRequest maxRows allRels proc apiRequest  =
     buildReadRequest fieldTree =
       let rootDepth = 0
           rootNodeName = if action == ActionRead then rootTableName else sourceCTEName in
-      foldr (treeEntry rootDepth) (Node (Select [] rootNodeName [] [] [] [] allRange, (rootNodeName, Nothing, Nothing, Nothing, rootDepth)) []) fieldTree
+      foldr (treeEntry rootDepth) (Node (Select [] rootNodeName Nothing [] [] [] [] allRange, (rootNodeName, Nothing, Nothing, Nothing, rootDepth)) []) fieldTree
       where
         treeEntry :: Depth -> Tree SelectItem -> ReadRequest -> ReadRequest
         treeEntry depth (Node fld@((fn, _),_,alias,relationDetail) fldForest) (Node (q, i) rForest) =
@@ -84,7 +84,7 @@ readRequest maxRows allRels proc apiRequest  =
           case fldForest of
             [] -> Node (q {select=fld:select q}, i) rForest
             _  -> Node (q, i) $
-                  foldr (treeEntry nxtDepth) (Node (Select [] fn [] [] [] [] allRange, (fn, Nothing, alias, relationDetail, nxtDepth)) []) fldForest:rForest
+                  foldr (treeEntry nxtDepth) (Node (Select [] fn Nothing [] [] [] [] allRange, (fn, Nothing, alias, relationDetail, nxtDepth)) []) fldForest:rForest
 
     relations :: [Relation]
     relations = case action of
@@ -116,7 +116,7 @@ treeRestrictRange maxRows_ request = pure $ nodeRestrictRange maxRows_ `fmap` re
 augumentRequestWithJoin :: Schema ->  [Relation] ->  ReadRequest -> Either ApiRequestError ReadRequest
 augumentRequestWithJoin schema allRels request =
   addRelations schema allRels Nothing request
-  >>= addJoinConditions schema
+  >>= addJoinConditions schema Nothing
 
 addRelations :: Schema -> [Relation] -> Maybe ReadRequest -> ReadRequest -> Either ApiRequestError ReadRequest
 addRelations schema allRelations parentNode (Node (query@Select{from=tbl}, (nodeName, _, alias, relationDetail, depth)) forest) =
@@ -216,10 +216,11 @@ findRelation schema allRelations nodeTableName parentNodeTableName relationDetai
         )
   ) allRelations
 
-addJoinConditions :: Schema -> ReadRequest -> Either ApiRequestError ReadRequest
-addJoinConditions schema (Node node@(query, nodeProps@(_, relation, _, _, _)) forest) =
+-- previousAlias is only used for the case of self joins
+addJoinConditions :: Schema -> Maybe Alias -> ReadRequest -> Either ApiRequestError ReadRequest
+addJoinConditions schema previousAlias (Node node@(query@Select{from=tbl}, nodeProps@(_, relation, _, _, depth)) forest) =
   case relation of
-    Just Relation{relType=Root} -> Node node  <$> updatedForest -- this is the root node
+    Just Relation{relType=Root} -> Node node <$> updatedForest -- this is the root node
     Just rel@Relation{relType=Parent} -> Node (augmentQuery rel, nodeProps) <$> updatedForest
     Just rel@Relation{relType=Child} -> Node (augmentQuery rel, nodeProps) <$> updatedForest
     Just rel@Relation{relType=Many, relLinkTable=(Just linkTable)} ->
@@ -227,13 +228,21 @@ addJoinConditions schema (Node node@(query, nodeProps@(_, relation, _, _, _)) fo
       Node (rq{implicitJoins=tableName linkTable:implicitJoins rq}, nodeProps) <$> updatedForest
     _ -> Left UnknownRelation
   where
-    updatedForest = mapM (addJoinConditions schema) forest
-    augmentQuery rel = foldr addJoinCond query (getJoinConditions rel)
-    addJoinCond :: JoinCondition -> ReadQuery -> ReadQuery
-    addJoinCond jc rq@Select{joinConditions=jcs} = rq{joinConditions=jc:jcs}
+    newAlias = case isSelfJoin <$> relation of
+      Just True
+        | depth /= 0 -> Just (tbl <> "_" <> show depth) -- root node doesn't get aliased
+        | otherwise  -> Nothing
+      _              -> Nothing
+    augmentQuery rel =
+      foldr
+        (\jc rq@Select{joinConditions=jcs} -> rq{joinConditions=jc:jcs})
+        query{fromAlias=newAlias}
+        (getJoinConditions previousAlias newAlias rel)
+    updatedForest = mapM (addJoinConditions schema newAlias) forest
 
-getJoinConditions :: Relation -> [JoinCondition]
-getJoinConditions (Relation Table{tableSchema=tSchema, tableName=tN} cols Table{tableName=ftN} fCols typ lt lc1 lc2) =
+-- previousAlias and newAlias are used in the case of self joins
+getJoinConditions :: Maybe Alias -> Maybe Alias -> Relation -> [JoinCondition]
+getJoinConditions previousAlias newAlias (Relation Table{tableSchema=tSchema, tableName=tN} cols Table{tableName=ftN} fCols typ lt lc1 lc2) =
   if | typ == Child || typ == Parent ->
         zipWith (toJoinCondition tN ftN) cols fCols
      | typ == Many ->
@@ -243,8 +252,10 @@ getJoinConditions (Relation Table{tableSchema=tSchema, tableName=tN} cols Table{
   where
     toJoinCondition :: Text -> Text -> Column -> Column -> JoinCondition
     toJoinCondition tb ftb c fc =
-      JoinCondition (QualifiedIdentifier tSchema tb, Nothing, colName c)
-                    (QualifiedIdentifier tSchema ftb, Nothing, colName fc)
+      let qi1 = QualifiedIdentifier tSchema tb
+          qi2 = QualifiedIdentifier tSchema ftb in
+        JoinCondition (maybe qi1 (QualifiedIdentifier mempty) newAlias, colName c)
+                      (maybe qi2 (QualifiedIdentifier mempty) previousAlias, colName fc)
 
 addFiltersOrdersRanges :: ApiRequest -> Either ApiRequestError (ReadRequest -> ReadRequest)
 addFiltersOrdersRanges apiRequest = foldr1 (liftA2 (.)) [