可以立即为已有数据库连接添加新层。
Adding new layers for existing database connections can be done right away.
允许在没有数据库连接的情况下使用保存的模型。
Let you work with a disconnected, saved model for the database connection.
而link则可被设为对现有数据库连接或对象的一个引用。
You can set link as a reference to an existing database connection link or object.
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