fix: nested empty embeds no longer return empty values and are correctly omitted

CHANGELOG.md

@@ -5,6 +5,10 @@ This project adheres to [Semantic Versioning](http://semver.org/).
 
 ## Unreleased
 
+### Fixed
+
+ - #3093, Nested empty embeds no longer show empty values and are correctly omitted - @laurenceisla
+
 ## [12.2.1] - 2024-06-27
 
 ### Fixed

src/PostgREST/Plan.hs

@@ -622,7 +622,11 @@ generateRelSelectField (Node ReadPlan{relToParent=Just rel, select, relName, rel
   where
     rsSelName = fromMaybe relName relAlias
     rsEmbedMode = if relIsToOne rel then JsonObject else JsonArray
-    rsEmptyEmbed = null select && null forest
+    rsEmptyEmbed = hasOnlyNullEmbed (null select) forest
+    hasOnlyNullEmbed = foldr checkIfNullEmbed
+    checkIfNullEmbed :: ReadPlanTree -> Bool -> Bool
+    checkIfNullEmbed (Node ReadPlan{select=s} f) isNullEmbed =
+      isNullEmbed && hasOnlyNullEmbed (null s) f
 generateRelSelectField _ = Nothing
 
 generateSpreadSelectFields :: ReadPlan -> [SpreadSelectField]

test/spec/Feature/Query/QuerySpec.hs

@@ -1218,6 +1218,20 @@ spec actualPgVersion = do
         [json|[{"id":1,"name":"Angela Martin"}]|]
         { matchHeaders = [matchContentTypeJson] }
 
+    it "works on nested relationships" $ do
+      get "/users?select=*,users_tasks(tasks(projects()))" `shouldRespondWith`
+        [json| [{"id":1,"name":"Angela Martin"}, {"id":2,"name":"Michael Scott"}, {"id":3,"name":"Dwight Schrute"}]|]
+        { matchHeaders = [matchContentTypeJson] }
+      get "/users?select=*,users_tasks!inner(tasks!inner(projects()))&users_tasks.tasks.id=eq.3" `shouldRespondWith`
+        [json| [{"id":1,"name":"Angela Martin"}]|]
+        { matchHeaders = [matchContentTypeJson] }
+      get "/users?select=*,tasks(projects(clients()),users_tasks())" `shouldRespondWith`
+        [json| [{"id":1,"name":"Angela Martin"}, {"id":2,"name":"Michael Scott"}, {"id":3,"name":"Dwight Schrute"}]|]
+        { matchHeaders = [matchContentTypeJson] }
+      get "/users?select=*,tasks!inner(projects(clients()),users_tasks(),name)&tasks.id=eq.3" `shouldRespondWith`
+        [json| [{"id":1,"name":"Angela Martin","tasks":[{"name": "Design w10"}]}]|]
+        { matchHeaders = [matchContentTypeJson] }
+
   context "empty root select" $
     it "gives all columns" $ do
       get "/projects?select=" `shouldRespondWith`
@@ -1413,4 +1427,3 @@ spec actualPgVersion = do
       get "/infinite_recursion?select=*" `shouldRespondWith`
         [json|{"code":"42P17","message":"infinite recursion detected in rules for relation \"infinite_recursion\"","details":null,"hint":null}|]
         { matchStatus = 500 }
-