hibernate - Does JPA @Id provide value if the table is auto-incrementing? -

this searched high , low in hibernate docs , surprisingly couldn't find answer for.

almost canonical examples of hibernate/jpa demonstrate configuring primary key via @id annotation so:

// groovy pseudo-code! @entity class car {   @id   @column(name = "car_id")   long id    @column(name = "car_make")   string make    @column(name = "car_model")   string model } 

but, if have pre-existing database, , if plan on using hibernate merely validate database instead of create 1 me (via hibernate.hbm2ddl.auto = validate), , if db table configured auto-incrementing primary key field, of value (at application layer) @id provide me? meaning, given:

• hibernate.hbm2ddl.auto = validate; and
• the table/entity has auto-incrementing pk (such mysql auto_incrementing)

...then matter application whether entity class has @id in or not? why couldn't write like:

// groovy pseudo-code! @entity class car {   @column(name = "car_id")   long id    @column(name = "car_make")   string make    @column(name = "car_model")   string model } 

or @id still provide value app in way (if so, how)?

does jpa @id provide value if table auto-incrementing?

short answer no. annotation @id specifies primary key of entity. if want value auto-generated have annotate field @generatedvalue indicating appropriate generationtype strategy, i.e.: identity:

@entity class car {      @id     @generatedvalue(strategy = generationtype.identity)     @column(name = "car_id")     long id      /... } 

note auto-increment or serial types not supported rdbms, i.e: oracle not have auto-increment type can create , use sequence instead.