Respect structs which implement sql.Scanner

scanner.go

@@ -165,6 +165,8 @@ func initFieldTag(sliceItem reflect.Value, fieldTagMap *map[string]reflect.Value
 	}
 }
 
+var sqlScannerType = reflect.TypeOf((*sql.Scanner)(nil)).Elem()
+
 func structPointers(sliceItem reflect.Value, cols []string, strict bool) []interface{} {
 	pointers := make([]interface{}, 0, len(cols))
 	fieldTag := make(map[string]reflect.Value, len(cols))
@@ -179,6 +181,13 @@ func structPointers(sliceItem reflect.Value, cols []string, strict bool) []inter
 				fieldVal = reflect.ValueOf(nil)
 			} else {
 				fieldVal = sliceItem.FieldByName(ScannerMapper(colName))
+				if fieldVal == (reflect.Value{}) {
+					if sliceItem.Addr().Type().Implements(sqlScannerType) {
+						// probably this is a custom struct that implements sql.Scanner.
+						// do our best and don't set "nothing" as a pointer
+						fieldVal = sliceItem
+					}
+				}
 			}
 		}
 		if !fieldVal.IsValid() || !fieldVal.CanSet() {

sql_scanner_test.go

@@ -0,0 +1,72 @@
+package scan_test
+
+import (
+	"fmt"
+	"strconv"
+	"testing"
+
+	"github.com/stretchr/testify/require"
+
+	"github.com/blockloop/scan/v2"
+)
+
+func TestCustomScanner(t *testing.T) {
+	db := mustDB(t.Name(), `
+		CREATE TABLE test
+		(
+			id int PRIMARY KEY,
+			data int NOT NULL
+		)`,
+		`INSERT INTO test (id, data) VALUES (1, 123), (2, 234)`,
+	)
+	t.Cleanup(func() { db.Close() })
+
+	const (
+		selectOneQuery = `SELECT data FROM test WHERE id = 1`
+		selectAllQuery = `SELECT data FROM test`
+	)
+
+	t.Run("scan.Row must work", func(t *testing.T) {
+		var data customScanner
+		rows, err := db.Query(selectOneQuery)
+		require.NoError(t, err)
+
+		err = scan.Row(&data, rows)
+		require.NoError(t, err)
+		require.Equal(t, customScanner{v: 123}, data)
+	})
+
+	t.Run("scan.Rows must work", func(t *testing.T) {
+		var data []customScanner
+		rows, err := db.Query(selectAllQuery)
+		require.NoError(t, err)
+
+		err = scan.Rows(&data, rows)
+		require.NoError(t, err)
+		require.ElementsMatch(t, []customScanner{{v: 123}, {v: 234}}, data)
+	})
+
+}
+
+type customScanner struct {
+	v int64
+}
+
+func (c *customScanner) Scan(src interface{}) error {
+	switch v := src.(type) {
+	case int64:
+		*c = customScanner{v: v}
+	case []byte: // for ramsql
+		n, err := strconv.ParseInt(string(v), 10, 64)
+		if err != nil {
+			return fmt.Errorf("parse int: %w", err)
+		}
+		*c = customScanner{v: n}
+	case nil:
+		return nil
+	default:
+		return fmt.Errorf("unsupported type %T", src)
+	}
+
+	return nil
+}