【第一章 Design】 2 Cayenne 持久化对象生存期-优快云博客

本文介绍Apache Cayenne框架中持久化对象的状态及其转换过程。详细解释了TRANSIENT、NEW、COMMITTED、MODIFIED、HOLLOW和DELETED等状态，并说明了这些状态如何随数据上下文的变化而变化。

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持久化对象的生存期可以描述为可以相互转化的几种状态，并且预定义了整数型的常量值，定义在org.apache.cayenne.PersistenceState 类中。在应用程序和持久化对象或者Cayenne上下文交互时，状态发生变化。无论什么时候状态发生了变化，Cayenne会调用setPersistenceState()方法，自动更新所有受到影响的对象的persistenceState的属性值。

新建对象的状态变化:

自动获取或者提交对象状态变化:

预定义的几种状态:

状态	值	描述
TRANSIENT	1	The object is not registered in a `DataContext` and will not persist.
NEW	2	The object is freshly registered in a `DataContext`, but has not been persisted to the database (there is no matching database record).
COMMITTED	3	The object is registered in a `DataContext` and has been persisted to the database (there is a matching database record).
MODIFIED	4	The object is registered in a `DataContext` and there is a matching database record and the object has been modified in memory, but the changes have not yet been persisted back to the database.
HOLLOW	5	The object is registered in a `DataContext` and has a corresponding database row, but the values have not yet been fetched from the database. The values will be fetched/faulted from the database automatically by Cayenne if any fields are requested from the object.
DELETED	6	The object is registered in a `DataContext` and will be deleted from the database upon commit.