From 2ecbb8e36cd1658f0ceb05785180dfb21dd6f3f4 Mon Sep 17 00:00:00 2001
From: JP Roemer <2822534+0rax@users.noreply.github.com>
Date: Mon, 22 Jul 2024 11:09:34 +0200
Subject: [PATCH 1/2] fix: handle empty hstore gracefuly in pgdialect

---
 dialect/pgdialect/hstore_parser.go | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/dialect/pgdialect/hstore_parser.go b/dialect/pgdialect/hstore_parser.go
index df9918219..fec401786 100644
--- a/dialect/pgdialect/hstore_parser.go
+++ b/dialect/pgdialect/hstore_parser.go
@@ -16,7 +16,7 @@ type hstoreParser struct {
 
 func newHStoreParser(b []byte) *hstoreParser {
 	p := new(hstoreParser)
-	if len(b) < 6 || b[0] != '"' {
+	if len(b) != 0 && (len(b) < 6 || b[0] != '"') {
 		p.err = fmt.Errorf("pgdialect: can't parse hstore: %q", b)
 		return p
 	}
@@ -83,7 +83,7 @@ func (p *hstoreParser) readNext() error {
 	default:
 		value := p.p.ReadLiteral(ch)
 		if bytes.Equal(value, []byte("NULL")) {
-			value = nil
+			p.value = ""
 		}
 		p.skipComma()
 		return nil

From 1d90ace98e34262062eb3db0c6882ea4f7fece2f Mon Sep 17 00:00:00 2001
From: JP Roemer <2822534+0rax@users.noreply.github.com>
Date: Mon, 22 Jul 2024 11:10:23 +0200
Subject: [PATCH 2/2] chore: add test cases for hstore (empty hstore & query
 appender)

---
 dialect/pgdialect/append_test.go        | 39 +++++++++++++++++++++++++
 dialect/pgdialect/hstore_parser_test.go |  2 ++
 internal/dbtest/pg_test.go              | 16 ++++++++++
 3 files changed, 57 insertions(+)
 create mode 100644 dialect/pgdialect/append_test.go

diff --git a/dialect/pgdialect/append_test.go b/dialect/pgdialect/append_test.go
new file mode 100644
index 000000000..eeadb5e24
--- /dev/null
+++ b/dialect/pgdialect/append_test.go
@@ -0,0 +1,39 @@
+package pgdialect
+
+import (
+	"fmt"
+	"reflect"
+	"testing"
+
+	"github.com/stretchr/testify/require"
+	"github.com/uptrace/bun/schema"
+)
+
+func TestHStoreAppender(t *testing.T) {
+	tests := []struct {
+		input      map[string]string
+		expectedIn []string // maps being unsorted, multiple expected output are valid
+	}{
+		{nil, []string{`NULL`}},
+		{map[string]string{}, []string{`''`}},
+
+		{map[string]string{"": ""}, []string{`'""=>""'`}},
+		{map[string]string{`\`: `\`}, []string{`'"\\"=>"\\"'`}},
+		{map[string]string{"'": "'"}, []string{`'"''"=>"''"'`}},
+		{map[string]string{`'"{}`: `'"{}`}, []string{`'"''\"{}"=>"''\"{}"'`}},
+
+		{map[string]string{"1": "2", "3": "4"}, []string{`'"1"=>"2","3"=>"4"'`, `'"3"=>"4","1"=>"2"'`}},
+		{map[string]string{"1": ""}, []string{`'"1"=>""'`}},
+		{map[string]string{"1": "NULL"}, []string{`'"1"=>"NULL"'`}},
+		{map[string]string{"{1}": "{2}", "{3}": "{4}"}, []string{`'"{1}"=>"{2}","{3}"=>"{4}"'`, `'"{3}"=>"{4}","{1}"=>"{2}"'`}},
+	}
+
+	appendFunc := pgDialect.hstoreAppender(reflect.TypeOf(map[string]string{}))
+
+	for i, test := range tests {
+		t.Run(fmt.Sprint(i), func(t *testing.T) {
+			got := appendFunc(schema.NewFormatter(pgDialect), []byte{}, reflect.ValueOf(test.input))
+			require.Contains(t, test.expectedIn, string(got))
+		})
+	}
+}
diff --git a/dialect/pgdialect/hstore_parser_test.go b/dialect/pgdialect/hstore_parser_test.go
index 2323611c2..6b3d663a6 100644
--- a/dialect/pgdialect/hstore_parser_test.go
+++ b/dialect/pgdialect/hstore_parser_test.go
@@ -12,6 +12,8 @@ func TestHStoreParser(t *testing.T) {
 		s string
 		m map[string]string
 	}{
+		{``, map[string]string{}},
+
 		{`""=>""`, map[string]string{"": ""}},
 		{`"\\"=>"\\"`, map[string]string{`\`: `\`}},
 		{`"'"=>"'"`, map[string]string{"'": "'"}},
diff --git a/internal/dbtest/pg_test.go b/internal/dbtest/pg_test.go
index 103d68170..21e80b852 100644
--- a/internal/dbtest/pg_test.go
+++ b/internal/dbtest/pg_test.go
@@ -750,6 +750,22 @@ func TestPostgresHStoreQuote(t *testing.T) {
 	require.Equal(t, wanted, m)
 }
 
+func TestPostgresHStoreEmpty(t *testing.T) {
+	db := pg(t)
+	t.Cleanup(func() { db.Close() })
+
+	_, err := db.Exec(`CREATE EXTENSION IF NOT EXISTS HSTORE;`)
+	require.NoError(t, err)
+
+	wanted := map[string]string{}
+	m := make(map[string]string)
+	err = db.NewSelect().
+		ColumnExpr("?::hstore", pgdialect.HStore(wanted)).
+		Scan(ctx, pgdialect.HStore(&m))
+	require.NoError(t, err)
+	require.Equal(t, wanted, m)
+}
+
 func TestPostgresSkipupdateField(t *testing.T) {
 	type Model struct {
 		ID        int64 `bun:",pk,autoincrement"`