From 887948d259c2e1c5d1ef6554dcb1c67d0ae11769 Mon Sep 17 00:00:00 2001
From: steve-chavez <stevechavezast@gmail.com>
Date: Thu, 27 Apr 2023 15:09:57 -0500
Subject: [PATCH] fix: missing=default error msg on generated column

---
 CHANGELOG.md                          |  1 +
 src/PostgREST/SchemaCache.hs          | 22 +++++++++++++++------
 test/spec/Feature/Query/InsertSpec.hs | 28 +++++++++++++++++++++++++--
 test/spec/fixtures/schema.sql         | 16 +++++++++++++++
 4 files changed, 59 insertions(+), 8 deletions(-)

diff --git a/CHANGELOG.md b/CHANGELOG.md
index 09a317bcd..e76b14a10 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -8,6 +8,7 @@ This project adheres to [Semantic Versioning](http://semver.org/).
 ### Fixed
 
  - #2762, Fixes "permission denied for schema" error during schema cache load - @steve-chavez
+ - #2756, Fix bad error message on generated columns when using `Prefer: missing=default` - @steve-chavez
 
 ## [11.0.0] - 2023-04-16
 
diff --git a/src/PostgREST/SchemaCache.hs b/src/PostgREST/SchemaCache.hs
index 59ce5f205..b86eded9e 100644
--- a/src/PostgREST/SchemaCache.hs
+++ b/src/PostgREST/SchemaCache.hs
@@ -40,7 +40,7 @@ import Text.InterpolatedString.Perl6 (q)
 
 import PostgREST.Config.Database          (pgVersionStatement)
 import PostgREST.Config.PgVersion         (PgVersion, pgVersion100,
-                                           pgVersion110)
+                                           pgVersion110, pgVersion120)
 import PostgREST.SchemaCache.Identifiers  (AccessSet, FieldName,
                                            QualifiedIdentifier (..),
                                            Schema)
@@ -516,11 +516,8 @@ tablesSqlQuery pgVer =
           c.relname::name AS table_name,
           a.attname::name AS column_name,
           d.description AS description,
-          CASE
-            WHEN seqclass.relname is null
-              THEN pg_get_expr(ad.adbin, ad.adrelid)::text
-              ELSE format('nextval(%s)', quote_literal(seqsch.nspname || '.' || seqclass.relname))
-          END AS column_default,
+  |] <> columnDefault <>
+  [q|
           not (a.attnotnull OR t.typtype = 'd' AND t.typnotnull) AS is_nullable,
               CASE
                   WHEN t.typtype = 'd' THEN
@@ -708,6 +705,19 @@ tablesSqlQuery pgVer =
   "ORDER BY table_schema, table_name"
   where
     relIsPartition = if pgVer >= pgVersion100 then " AND not c.relispartition " else mempty
+    columnDefault
+      | pgVer >= pgVersion120 = [q|
+          CASE
+            WHEN a.attidentity  = 'd' THEN format('nextval(%s)', quote_literal(seqsch.nspname || '.' || seqclass.relname))
+            WHEN a.attgenerated = 's' THEN null
+            ELSE pg_get_expr(ad.adbin, ad.adrelid)::text
+          END AS column_default,|]
+      | pgVer >= pgVersion100 = [q|
+          CASE
+            WHEN a.attidentity = 'd' THEN format('nextval(%s)', quote_literal(seqsch.nspname || '.' || seqclass.relname))
+            ELSE pg_get_expr(ad.adbin, ad.adrelid)::text
+          END AS column_default,|]
+      | otherwise  = "pg_get_expr(ad.adbin, ad.adrelid)::text as column_default,"
 
 -- | Gets many-to-one relationships and one-to-one(O2O) relationships, which are a refinement of the many-to-one's
 allM2OandO2ORels :: PgVersion -> Bool -> SQL.Statement () [Relationship]
diff --git a/test/spec/Feature/Query/InsertSpec.hs b/test/spec/Feature/Query/InsertSpec.hs
index fbb933d1b..9babe03e9 100644
--- a/test/spec/Feature/Query/InsertSpec.hs
+++ b/test/spec/Feature/Query/InsertSpec.hs
@@ -13,7 +13,8 @@ import Text.Heredoc
 
 import PostgREST.Config.PgVersion (PgVersion, pgVersion100,
                                    pgVersion110, pgVersion112,
-                                   pgVersion130)
+                                   pgVersion120, pgVersion130,
+                                   pgVersion140)
 
 import Protolude  hiding (get)
 import SpecHelper
@@ -496,7 +497,7 @@ spec actualPgVersion = do
               }
 
         when (actualPgVersion >= pgVersion100) $
-          it "inserts a default on a generated by default as identity column" $ do
+          it "inserts a default on a generated by default as identity column" $
             request methodPost "/channels?columns=id,data,slug&select=data,slug" [("Prefer", "return=representation"), ("Prefer", "missing=default")]
                 [json| { "slug": "foo" } |]
               `shouldRespondWith`
@@ -505,6 +506,29 @@ spec actualPgVersion = do
                 , matchHeaders = ["Preference-Applied" <:> "missing=default"]
                 }
 
+        when (actualPgVersion >= pgVersion120) $
+          it "fails with a good error message on generated always columns" $
+            request methodPost "/foo?columns=a,b" [("Prefer", "return=representation"), ("Prefer", "missing=default")]
+                [json| [
+                  {"a": "val"},
+                  {"a": "val", "b": "val"}
+                ]|]
+              `shouldRespondWith`
+                (if actualPgVersion < pgVersion140
+                  then [json| {
+                    "code": "42601",
+                    "details": "Column \"b\" is a generated column.",
+                    "hint": null,
+                    "message": "cannot insert into column \"b\""
+                  }|]
+                  else [json| {
+                    "code": "428C9",
+                    "details": "Column \"b\" is a generated column.",
+                    "hint": null,
+                    "message": "cannot insert a non-DEFAULT value into column \"b\""
+                  }|])
+                { matchStatus  = 400 }
+
     it "inserts json that has duplicate keys" $ do
       request methodPost "/tbl_w_json" [("Prefer", "return=representation")]
           [json| { "data": { "a": 1, "a": 2 }, "id": 3 } |]
diff --git a/test/spec/fixtures/schema.sql b/test/spec/fixtures/schema.sql
index fbb1bc3d1..d78f0eacb 100644
--- a/test/spec/fixtures/schema.sql
+++ b/test/spec/fixtures/schema.sql
@@ -3128,3 +3128,19 @@ LANGUAGE sql
 AS $$
   select current_setting('is_superuser')::boolean;
 $$;
+
+DO $do$
+BEGIN
+  IF current_setting('server_version_num')::INT >= 120000 THEN
+    CREATE TABLE test.foo (
+      a text,
+      b text GENERATED ALWAYS AS (
+          case WHEN a = 'telegram' THEN 'im'
+               WHEN a = 'proton' THEN 'email'
+               WHEN a = 'infinity' THEN 'idea'
+               ELSE 'bad idea'
+          end) stored
+    );
+  END IF;
+END
+$do$;