Support NULL value replacement for custom types

paginator/paginator.go

@@ -184,7 +184,12 @@ func (p *Paginator) decodeCursor(dest interface{}) (result []interface{}, err er
 	}
 	// replace null values
 	for i := range result {
-		if isNil(result[i]) {
+		value := result[i]
+		// for custom types, evaluate isNil on the underlying value
+		if ct, ok := result[i].(cursor.CustomType); ok && p.rules[i].CustomType != nil {
+			value, err = ct.GetCustomTypeValue(p.rules[i].CustomType.Meta)
+		}
+		if isNil(value) {
 			result[i] = p.rules[i].NULLReplacement
 		}
 	}

paginator/paginator_paginate_test.go

@@ -669,6 +669,87 @@ func (s *paginatorSuite) TestPaginateCustomTypeString() {
 	s.assertIDs(p1, 9, 8, 7)
 }
 
+func (s *paginatorSuite) TestPaginateCustomTypeNullable() {
+	s.givenOrders([]order{
+		{
+			ID:     1,
+			Remark: ptrStr("1"),
+			NullableCustomData: NullString{
+				String: "A",
+				Valid:  true,
+			},
+		},
+		{
+			ID:     2,
+			Remark: ptrStr("2"),
+			NullableCustomData: NullString{
+				String: "",
+				Valid:  false,
+			},
+		},
+		{
+			ID:     3,
+			Remark: ptrStr("2"),
+			NullableCustomData: NullString{
+				String: "B",
+				Valid:  true,
+			},
+		},
+	})
+
+	text := "text"
+	cfg := &Config{
+		Limit: 1,
+		Rules: []Rule{
+			{
+				Key:   "Remark",
+				Order: ASC,
+			},
+			{
+				Key:     "NullableCustomData",
+				Order:   ASC,
+				SQLType: &text,
+				CustomType: &CustomType{
+					Type: reflect.TypeOf(NullString{}),
+				},
+				NULLReplacement: "",
+			},
+		},
+	}
+
+	var p1 []order
+	_, c, _ := New(cfg).Paginate(s.db, &p1)
+	s.Len(p1, 1)
+	s.assertForwardOnly(c)
+	s.assertIDs(p1, 1)
+
+	var p2 []order
+	_, c, _ = New(cfg, WithAfter(*c.After)).Paginate(s.db, &p2)
+	s.Len(p2, 1)
+	s.assertBothDirections(c)
+	s.assertIDs(p2, 2)
+
+	var p3 []order
+	_, c, _ = New(cfg, WithAfter(*c.After)).Paginate(s.db, &p3)
+	s.Len(p3, 1)
+	s.assertBackwardOnly(c)
+	s.assertIDs(p3, 3)
+
+	// back to page 2
+	var p4 []order
+	_, c, _ = New(cfg, WithBefore(*c.Before)).Paginate(s.db, &p4)
+	s.Len(p4, 1)
+	s.assertBothDirections(c)
+	s.assertIDs(p4, 2)
+
+	// back to page 1
+	var p5 []order
+	_, c, _ = New(cfg, WithBefore(*c.Before)).Paginate(s.db, &p5)
+	s.Len(p5, 1)
+	s.assertForwardOnly(c)
+	s.assertIDs(p5, 1)
+}
+
 /* compatibility */
 
 func (s *paginatorSuite) TestPaginateConsistencyBetweenBuilderAndKeyOptions() {

paginator/paginator_test.go

@@ -1,6 +1,8 @@
 package paginator
 
 import (
+	"bytes"
+	"database/sql"
 	"database/sql/driver"
 	"encoding/json"
 	"errors"
@@ -24,10 +26,11 @@ func TestPaginator(t *testing.T) {
 /* models */
 
 type order struct {
-	ID        int       `gorm:"primaryKey"`
-	Remark    *string   `gorm:"type:varchar(30)"`
-	CreatedAt time.Time `gorm:"type:timestamp;not null"`
-	Data      JSON      `gorm:"type:jsonb"`
+	ID                 int        `gorm:"primaryKey"`
+	Remark             *string    `gorm:"type:varchar(30)"`
+	CreatedAt          time.Time  `gorm:"type:timestamp;not null"`
+	Data               JSON       `gorm:"type:jsonb"`
+	NullableCustomData NullString `gorm:"type:varchar(30)"`
 }
 
 type item struct {
@@ -80,6 +83,55 @@ func (j JSON) GetCustomTypeValue(meta interface{}) (interface{}, error) {
 	return i, nil
 }
 
+/* NullString type used for testing custom types with nullable values */
+
+type NullString sql.NullString
+
+func (ns NullString) MarshalJSON() ([]byte, error) {
+	if !ns.Valid {
+		return []byte("null"), nil
+	}
+	return json.Marshal(ns.String)
+}
+
+func (ns *NullString) UnmarshalJSON(b []byte) error {
+	isNull := bytes.Equal(b, []byte("null"))
+	ns.Valid = !isNull
+
+	if isNull {
+		ns.String = "null"
+		return nil
+	}
+	return json.Unmarshal(b, &ns.String)
+}
+
+func (ns NullString) Value() (driver.Value, error) {
+	if !ns.Valid {
+		return nil, nil
+	}
+	return ns.String, nil
+}
+
+func (ns *NullString) Scan(value interface{}) error {
+	if value == nil {
+		ns.String = ""
+		ns.Valid = false
+	} else if strValue, ok := value.(string); ok {
+		ns.Valid = true
+		ns.String = strValue
+	} else {
+		return errors.New("unsupported type")
+	}
+	return nil
+}
+
+func (ns NullString) GetCustomTypeValue(meta interface{}) (interface{}, error) {
+	if ns.Valid {
+		return ns.String, nil
+	}
+	return nil, nil
+}
+
 /* paginator suite */
 
 type paginatorSuite struct {