JPA tables are ID is mandatory?

Question

I saw that the ID type is defined in every JPA table. Is it mandatory? Or is there any option that I can get class without the ID member?

Its not mandatory in JDO, in that you can have tables without primary key (see "nondurable identity"), but is in JPA. — DataNucleus, Jan 27 '13 at 08:45

Hui Zheng · Accepted Answer · 2013-01-27T08:57:15.697

3

Id(i.e. primary key) is mandatory in JPA. As JSR317(Java Persistence API, which could be downloaded here) chapter 2.4 said(first sentence):

Every entity must have a primary key

BTW, besides Id annotation, one can also use EmbeddedId annotation for composite primary keys.

edited Jan 27 '13 at 08:57

answered Jan 27 '13 at 07:59

Hui Zheng

And the type of the ID can be any type ? I tried to find the documentation without success – Stefan Strooves Jan 27 '13 at 08:09
JPA poses some restrictions on ID type(e.g. primary key class must be serializable), you can read the specification from the link I gave for more details,(esp. chapter 2.4 which I mentioned in the answer). – Hui Zheng Jan 27 '13 at 08:17

score 3 · Answer 2 · answered Jan 27 '13 at 08:14

Id is required by JPA, but it is not required that the Id specified in your mapping match the Id in your database.

For instance you can map a table with no id to a jpa entity. To do it just specify that the "Jpa Id" is the combination of all columns.

Note that for performence reason, it's important to have a good index on column(s) specified as Id in Jpa

2 Answers2