Add BeginTx for parity with sql.DB.BeginTx (go-gorm#2227)

interface.go

@@ -1,6 +1,9 @@
 package gorm
 
-import "database/sql"
+import (
+	"context"
+	"database/sql"
+)
 
 // SQLCommon is the minimal database connection functionality gorm requires.  Implemented by *sql.DB.
 type SQLCommon interface {
@@ -12,6 +15,7 @@ type SQLCommon interface {
 
 type sqlDb interface {
 	Begin() (*sql.Tx, error)
+	BeginTx(ctx context.Context, opts *sql.TxOptions) (*sql.Tx, error)
 }
 
 type sqlTx interface {

main.go

@@ -1,6 +1,7 @@
 package gorm
 
 import (
+	"context"
 	"database/sql"
 	"errors"
 	"fmt"
@@ -503,11 +504,16 @@ func (s *DB) Debug() *DB {
 	return s.clone().LogMode(true)
 }
 
-// Begin begin a transaction
+// Begin begins a transaction
 func (s *DB) Begin() *DB {
+	return s.BeginTx(context.Background(), &sql.TxOptions{})
+}
+
+// BeginTX begins a transaction with options
+func (s *DB) BeginTx(ctx context.Context, opts *sql.TxOptions) *DB {
 	c := s.clone()
 	if db, ok := c.db.(sqlDb); ok && db != nil {
-		tx, err := db.Begin()
+		tx, err := db.BeginTx(ctx, opts)
 		c.db = interface{}(tx).(SQLCommon)
 
 		c.dialect.SetDB(c.db)

main_test.go

@@ -1,6 +1,7 @@
 package gorm_test
 
 import (
+	"context"
 	"database/sql"
 	"database/sql/driver"
 	"fmt"
@@ -471,6 +472,40 @@ func TestTransaction_NoErrorOnRollbackAfterCommit(t *testing.T) {
 	}
 }
 
+func TestTransactionReadonly(t *testing.T) {
+	dialect := os.Getenv("GORM_DIALECT")
+	if dialect == "" {
+		dialect = "sqlite"
+	}
+	switch dialect {
+	case "mssql", "sqlite":
+		t.Skipf("%s does not support readonly transactions\n", dialect)
+	}
+
+	tx := DB.Begin()
+	u := User{Name: "transcation"}
+	if err := tx.Save(&u).Error; err != nil {
+		t.Errorf("No error should raise")
+	}
+	tx.Commit()
+
+	tx = DB.BeginTx(context.Background(), &sql.TxOptions{ReadOnly: true})
+	if err := tx.First(&User{}, "name = ?", "transcation").Error; err != nil {
+		t.Errorf("Should find saved record")
+	}
+
+	if sqlTx, ok := tx.CommonDB().(*sql.Tx); !ok || sqlTx == nil {
+		t.Errorf("Should return the underlying sql.Tx")
+	}
+
+	u = User{Name: "transcation-2"}
+	if err := tx.Save(&u).Error; err == nil {
+		t.Errorf("Error should have been raised in a readonly transaction")
+	}
+
+	tx.Rollback()
+}
+
 func TestRow(t *testing.T) {
 	user1 := User{Name: "RowUser1", Age: 1, Birthday: parseTime("2000-1-1")}
 	user2 := User{Name: "RowUser2", Age: 10, Birthday: parseTime("2010-1-1")}