Question

Hello and happy new year for everyone.

I need to insert a record at the end of a table (the table has not set autoincrement) using JPA.

I know I could get the last id (integer) and apply to the entity before insert, but how could that be done? Which way would be most effective?

Answer 1

Well, while i do not know where the end of a table really is, JPA has a lot of options for plugging in ID generators.

One common option is to use a table of its own, having a counter for each entity you need an ID for (from http://download.oracle.com/docs/cd/B32110_01/web.1013/b28221/cmp30cfg001.htm).

@Id(generate=TABLE, generator="ADDRESS_TABLE_GENERATOR")
@TableGenerator(
name="ADDRESS_TABLE_GENERATOR", 
    tableName="EMPLOYEE_GENERATOR_TABLE", 
    pkColumnValue="ADDRESS_SEQ"
)
@Column(name="ADDRESS_ID")
public Integer getId() {
    return id;
 }

…other “Generator” strategies to be googled…

EDIT

I dare to reference @a_horse_with_no_name as he says he does not know about JPA. If you want to use native mechanisms like sequence (that are not available in every DB) you can declare such a generator in JPA, too.

I do not know what issues he encountered with the table approach – i know large installations running this successfully. But anyway, this depends on a lot of factors besides scalability, for example if you want this to be portable etc. Just lookup the different strategies and select the appropriate.