Support scan of custom types implementing sql.Scanner into array/tupl…

…e columns (#1129)

* fix(lib/column): support scan of custom types implementing sql.Scanner

Signed-off-by: Leonardo Di Donato <leodidonato@gmail.com>

* test: test for issue 1128

Signed-off-by: Leonardo Di Donato <leodidonato@gmail.com>

---------

Signed-off-by: Leonardo Di Donato <leodidonato@gmail.com>

lib/column/tuple.go

@@ -18,14 +18,16 @@
 package column
 
 import (
+	"database/sql"
 	"fmt"
-	"github.com/ClickHouse/ch-go/proto"
-	"github.com/google/uuid"
-	"github.com/shopspring/decimal"
 	"net"
 	"reflect"
 	"strings"
 	"time"
+
+	"github.com/ClickHouse/ch-go/proto"
+	"github.com/google/uuid"
+	"github.com/shopspring/decimal"
 )
 
 type Tuple struct {
@@ -209,6 +211,15 @@ func setJSONFieldValue(field reflect.Value, value reflect.Value) error {
 		return nil
 	}
 
+	// check if our target implements sql.Scanner
+	sqlScanner := reflect.TypeOf((*sql.Scanner)(nil)).Elem()
+	if fieldAddr := field.Addr(); field.Kind() != reflect.Ptr && fieldAddr.Type().Implements(sqlScanner) {
+		returns := fieldAddr.MethodByName("Scan").Call([]reflect.Value{value})
+		if len(returns) > 0 && returns[0].IsNil() {
+			return nil
+		}
+	}
+
 	return &ColumnConverterError{
 		Op:   "ScanRow",
 		To:   fmt.Sprintf("%T", field.Interface()),

tests/issues/1128_test.go

@@ -0,0 +1,88 @@
+package issues
+
+import (
+	"context"
+	"fmt"
+	"testing"
+
+	"github.com/ClickHouse/clickhouse-go/v2"
+	clickhouse_tests "github.com/ClickHouse/clickhouse-go/v2/tests"
+	"github.com/stretchr/testify/require"
+)
+
+const (
+	A SomeUint64AsString = iota + 1
+	B
+	C
+)
+
+type SomeUint64AsString uint64
+
+func (f *SomeUint64AsString) Scan(src any) error {
+	if t, ok := src.(uint64); ok {
+		*f = SomeUint64AsString(t)
+		return nil
+	}
+	if t, ok := src.(string); ok {
+		switch t {
+		case "A":
+			*f = A
+		case "B":
+			*f = B
+		case "C":
+			*f = C
+		default:
+			return fmt.Errorf("cannot scan %s into SomeUint64AsString", t)
+		}
+		return nil
+	}
+
+	return fmt.Errorf("cannot scan %T into SomeUint64AsString", src)
+}
+
+func (f SomeUint64AsString) String() string {
+	switch f {
+	case A:
+		return "A"
+	case B:
+		return "B"
+	case C:
+		return "C"
+	}
+	return ""
+}
+
+type Test struct {
+	Col1 []SomeUint64AsString `ch:"Col1"`
+}
+
+func Test1128(t *testing.T) {
+	var (
+		conn, err = clickhouse_tests.GetConnection("issues", clickhouse.Settings{
+			"max_execution_time":             60,
+			"allow_experimental_object_type": true,
+		}, nil, &clickhouse.Compression{
+			Method: clickhouse.CompressionLZ4,
+		})
+	)
+	ctx := context.Background()
+	require.NoError(t, err)
+	const ddl = "CREATE TABLE test_1128 (Col1 Array(String)) Engine MergeTree() ORDER BY tuple()"
+	require.NoError(t, conn.Exec(ctx, ddl))
+	defer func() {
+		conn.Exec(ctx, "DROP TABLE IF EXISTS test_1128")
+	}()
+
+	batch, err := conn.PrepareBatch(ctx, "INSERT INTO test_1128")
+	require.NoError(t, err)
+
+	data := Test{
+		Col1: []SomeUint64AsString{A, B, C},
+	}
+	require.NoError(t, batch.AppendStruct(&data))
+	require.NoError(t, batch.Send())
+
+	var res Test
+	require.NoError(t, conn.QueryRow(ctx, "SELECT * FROM test_1128").ScanStruct(&res))
+	require.Equal(t, []SomeUint64AsString{A, B, C}, res.Col1)
+}