[fix] 多次调用 Open() 错误

db.go

@@ -17,22 +17,20 @@ func (d *DB) SetLogger(f func(log Log)) *DB {
 }
 
 func Open(config map[string]DBConfig) *DB {
-	var configP = make(map[string]*DBConfig)
+	if Engine == nil {
+		Engine = &DB{
+			DatabaseManager: DatabaseManager{
+				Configs:     make(map[string]*DBConfig),
+				Connections: make(map[string]*Connection),
+			},
+		}
+	}
 
 	for name := range config {
 		c := config[name]
-		configP[name] = &c
+		Engine.Configs[name] = &c
 	}
 
-	db := DB{
-		DatabaseManager: DatabaseManager{
-			Configs:     configP,
-			Connections: make(map[string]*Connection),
-		},
-	}
-
-	Engine = &db
-
 	return Engine
 }