fix: Bug when Null Filtering on embedded resources

src/PostgREST/Query/SqlFragment.hs

@@ -336,7 +336,7 @@ pgFmtArrayLiteralForField values _ = unknownLiteral (pgBuildArrayLiteral values)
 
 
 pgFmtFilter :: QualifiedIdentifier -> CoercibleFilter -> SQL.Snippet
-pgFmtFilter _ (CoercibleFilterNullEmbed hasNot fld) = pgFmtIdent fld <> " IS " <> (if hasNot then "NOT" else mempty) <> " NULL"
+pgFmtFilter _ (CoercibleFilterNullEmbed hasNot fld) = pgFmtIdent fld <> " IS " <> (if not hasNot then "NOT " else mempty) <> "DISTINCT FROM NULL"
 pgFmtFilter _ (CoercibleFilter _ (NoOpExpr _)) = mempty -- TODO unreachable because NoOpExpr is filtered on QueryParams
 pgFmtFilter table (CoercibleFilter fld (OpExpr hasNot oper)) = notOp <> " " <> pgFmtField table fld <> case oper of
    Op op val  -> " " <> simpleOperator op <> " " <> pgFmtUnknownLiteralForField (unknownLiteral val) fld

test/spec/Feature/Query/RelatedQueriesSpec.hs

@@ -256,3 +256,22 @@ spec = describe "related queries" $ do
         { matchStatus  = 200
         , matchHeaders = [matchContentTypeJson]
         }
+
+    -- "?table=not.is.null" does a "table IS DISTINCT FROM NULL" instead of a "table IS NOT NULL"
+    -- https://github.com/PostgREST/postgrest/issues/2800#issuecomment-1720315818
+    it "embeds verifying that the entire target table row is not null" $ do
+      get "/table_b?select=name,table_a(name)&table_a=not.is.null" `shouldRespondWith`
+        [json|[
+          {"name":"Test 1","table_a":{"name":"Not null 1"}},
+          {"name":"Test 2","table_a":{"name":null}}
+        ]|]
+        { matchStatus  = 200
+        , matchHeaders = [matchContentTypeJson]
+        }
+      get "/table_b?select=name,table_a()&table_a=is.null" `shouldRespondWith`
+        [json|[
+          {"name":"Test 3"}
+        ]|]
+        { matchStatus  = 200
+        , matchHeaders = [matchContentTypeJson]
+        }

test/spec/fixtures/data.sql

@@ -853,3 +853,8 @@ INSERT INTO datarep_next_two_todos VALUES (2, 1, 3, 'do these first');
 TRUNCATE TABLE bitchar_with_length CASCADE;
 INSERT INTO bitchar_with_length(bit, char) VALUES ('00000', 'aaaaa');
 INSERT INTO bitchar_with_length(bit, char) VALUES ('11111', 'bbbbb');
+
+TRUNCATE TABLE table_a CASCADE;
+INSERT INTO table_a(id, name) VALUES (1, 'Not null 1'), (2, null), (3, 'Not null 2');
+TRUNCATE TABLE table_b CASCADE;
+INSERT INTO table_b(table_a_id, name) VALUES (1, 'Test 1'), (2, 'Test 2'), (null, 'Test 3');

test/spec/fixtures/schema.sql

@@ -3437,3 +3437,13 @@ begin
       message = '{"code":"123","message":"ABC","details":"DEF"}';
 end
 $$;
+
+create table table_a (
+  id int primary key,
+  name text
+);
+
+create table table_b (
+  table_a_id int references table_a(id),
+  name text
+);