feat: add Connection to execute multiple commands in a single conne…

…ction; (go-gorm#4982)

finisher_api.go

@@ -515,6 +515,30 @@ func (db *DB) ScanRows(rows *sql.Rows, dest interface{}) error {
 	return tx.Error
 }
 
+// Connection  use a db conn to execute Multiple commands,this conn will put conn pool after it is executed.
+func (db *DB) Connection(fc func(tx *DB) error) (err error) {
+	if db.Error != nil {
+		return db.Error
+	}
+
+	tx := db.getInstance()
+	sqlDB, err := tx.DB()
+	if err != nil {
+		return
+	}
+
+	conn, err := sqlDB.Conn(tx.Statement.Context)
+	if err != nil {
+		return
+	}
+
+	defer conn.Close()
+	tx.Statement.ConnPool = conn
+	err = fc(tx)
+
+	return
+}
+
 // Transaction start a transaction as a block, return error will rollback, otherwise to commit.
 func (db *DB) Transaction(fc func(tx *DB) error, opts ...*sql.TxOptions) (err error) {
 	panicked := true

tests/connection_test.go

@@ -0,0 +1,48 @@
+package tests_test
+
+import (
+	"fmt"
+	"gorm.io/driver/mysql"
+	"gorm.io/gorm"
+	"testing"
+)
+
+func TestWithSingleConnection(t *testing.T) {
+
+	var expectedName = "test"
+	var actualName string
+
+	setSQL, getSQL := getSetSQL(DB.Dialector.Name())
+	if len(setSQL) == 0 || len(getSQL) == 0 {
+		return
+	}
+
+	err := DB.Connection(func(tx *gorm.DB) error {
+		if err := tx.Exec(setSQL, expectedName).Error; err != nil {
+			return err
+		}
+
+		if err := tx.Raw(getSQL).Scan(&actualName).Error; err != nil {
+			return err
+		}
+		return nil
+	})
+
+	if err != nil {
+		t.Errorf(fmt.Sprintf("WithSingleConnection should work, but got err %v", err))
+	}
+
+	if actualName != expectedName {
+		t.Errorf("WithSingleConnection() method should get correct value, expect: %v, got %v", expectedName, actualName)
+	}
+
+}
+
+func getSetSQL(driverName string) (string, string) {
+	switch driverName {
+	case mysql.Dialector{}.Name():
+		return "SET @testName := ?", "SELECT @testName"
+	default:
+		return "", ""
+	}
+}