fix: Location header with a null PK on a view (#1875)

Regression after #1475

src/PostgREST/Query/SqlFragment.hs

@@ -172,7 +172,7 @@ asBinaryF fieldName = "coalesce(string_agg(_postgrest_t." <> pgFmtIdent fieldNam
 locationF :: [Text] -> SqlFragment
 locationF pKeys = [qc|(
   WITH data AS (SELECT row_to_json(_) AS row FROM {sourceCTEName} AS _ LIMIT 1)
-  SELECT array_agg(json_data.key || '=eq.' || json_data.value)
+  SELECT array_agg(json_data.key || '=' || coalesce('eq.' || json_data.value, 'is.null'))
   FROM data CROSS JOIN json_each_text(data.row) AS json_data
   WHERE json_data.key IN ('{fmtPKeys}')
 )|]

test/Feature/InsertSpec.hs

@@ -527,7 +527,7 @@ spec actualPgVersion = do
             , matchHeaders = [ matchHeaderAbsent hLocation ]
             }
 
-    context "requesting header only representation" $
+    context "requesting header only representation" $ do
       it "returns a location header" $
         request methodPost "/compound_pk_view" [("Prefer", "return=headers-only")]
             [json|{"k1":1,"k2":"test","extra":2}|]
@@ -537,3 +537,13 @@ spec actualPgVersion = do
             , matchHeaders = [ "Location" <:> "/compound_pk_view?k1=eq.1&k2=eq.test"
                              , "Content-Range" <:> "*/*" ]
             }
+
+      it "should not throw and return location header when a PK is null" $
+        request methodPost "/test_null_pk_competitors_sponsors" [("Prefer", "return=headers-only")]
+            [json|{"id":1}|]
+          `shouldRespondWith`
+            ""
+            { matchStatus  = 201
+            , matchHeaders = [ "Location" <:> "/test_null_pk_competitors_sponsors?id=eq.1&sponsor_id=is.null"
+                             , "Content-Range" <:> "*/*" ]
+            }

test/fixtures/privileges.sql

@@ -37,6 +37,7 @@ GRANT ALL ON TABLE
     , projects
     , projects_view
     , projects_view_alt
+    , test_null_pk_competitors_sponsors
     , simple_pk
     , simple_pk2
     , tasks

test/fixtures/schema.sql

@@ -670,6 +670,28 @@ CREATE VIEW projects_view_alt AS
     projects.client_id as t_client_id
    FROM projects;
 
+CREATE TABLE sponsors (
+    id integer primary key,
+    name varchar(20) not null
+);
+
+CREATE TABLE competitors (
+    id integer primary key,
+    sponsor_id integer references sponsors(id),
+    full_name varchar(40) not null
+);
+
+CREATE VIEW test_null_pk_competitors_sponsors  AS
+SELECT c.id, s.id as sponsor_id
+FROM competitors c
+    LEFT JOIN sponsors s on c.sponsor_id = s.id;
+
+CREATE RULE test_null_pk_competitors_sponsors  AS
+    ON INSERT TO test_null_pk_competitors_sponsors DO INSTEAD
+    INSERT INTO competitors(id, full_name, sponsor_id)
+    VALUES (new.id, 'Competitor without sponsor', new.sponsor_id)
+    RETURNING id, sponsor_id;
+
 --
 -- Name: simple_pk; Type: TABLE; Schema: test; Owner: -
 --