Is it possible to have immutable fields in Hibernate/JPA?

 

In our application, we need to have fields that are assignable only once.

At first we thought of encapsulating the fields and making the setters private. However, some questions arouse:

  • Without a public setter, is Hibernate still able to map the field from the database?
  • Can I strip out the setter and make the field mutable only in the entity constructor?
  • Finally, is there any standard JPA way to make a field immutable?

    • Thanks in advance.

  • Ad. 1: I believe JPA uses plain private fields for both read and write if annotations are placed on fields and not on getters. Recently I discovered that Hibernate as an underlying JPA provider does not even need get*() and set*() methods at all. This was truly enlightening solution since from the beginning I thought Hibernate needs accessors. So the answer is: you don't need setters as far as Hibernate is concerned.

  • Ad. 2: However please note that Hibernate still needs no-arg constructor, otherwise it will fail to load entities with a descriptive exception. This is also a JPA requirement.

  • Ad. 3: No, there isn't. Remember that your collections would also had to be immutable.

    • Try 

    @Column(updatable = false)

    And make your setter private. (Leave your getter public if you want)

    I think this is the best practice.

    PS: JPA uses field access if you annotate your fields and uses getter/setter access if you annotate your getter method.

    In JPA 2.0 you have two ways to define what attributes should be persisted:

  • Access(FIELD) - the fields name are persisted,
  • Access(PROPERTY) - the properties name are persisted.

    • If no Access(-) annotation is used, the decision what access will be used depends on where you put your @Id annotation. If you put it next to your field - Access(FIELD) will be used. If you put it next to your accessor - Access(PROPERTY) will be used.

    Therefore, if you use Access(FIELD) you don't have to have an appropriate JavaBeans-style accessor for particular field. You can have a private field named 'myField' and a public setter for it named 'public setBlahBlah(-)'. The JPA will persist just the 'myField'.

    链接地址: http://www.djcxy.com/p/37006.html

    上一篇: JPA和Hibernate有什么区别？

    下一篇: Hibernate / JPA中可能有不可变的字段吗？