Hibernate 学习笔记3

Component

 

Component 是一个存值类型而非引用类型的被包含对象。--摘自《Hibernate Reference》

• Composite element
• Component在CUD的适合如何与数据库同步？
• Component可以作为对象的ID
• Component的作用
  • 将一张大表用Component进行拆分
• Component对象没有oid

继承映射

• 四种继承映射的类型
  • 一个层级对应一张表 <subclass> 缺点：子类声明的属性映射到得列不能有NOT NULL约束。（why？）
  • 一个子类对应一张表 <joined-subclass>
  • 一个具体类对应一张表 <union-subclass>
  • implicit polymorphism
• 基类需要声明所有的子类？
• It is possible to use different mapping strategies for different branches of the same inheritance hierarchy. You can then make use of implicit polymorphism to achieve polymorphism across the whole hierarchy. However, Hibernate does not support mixing <subclass>, <joined-subclass> and <union-subclass> mappings under the same root <class> element. It is possible to mix together the table per hierarchy and table per subclass strategies under the the same <class> element, by combining the <subclass> and <join> elements (see below for an example).

对象操作函数

• save
• update
• saveorupdate
• persist
• merge
• lock
• flush