JPA - Column annotation tip

Being an Oracle guy, I always have enjoyed getting into the guts of the SQL language. Recently I have been using JPA quite a bit recently and was frustrated by a particular problem. I needed to include a column that was generated off of other columns. For instance:

1. SELECT a, b, a+b FROM uninteresting_table;

In JPA-land, I started by writing my own fetch query and added a dummy field to the database table to accomplish this. Class, let's say this together, "This sucks.". However, I did perform a little bit of JPA trickery to get what I want, with the custom fetch query and no dummy data field. In your persistent bean you'll simply annotate your column as follows:

1. // Java code above....




3. @Column(name="a+b", insertable=false, updatable=false)


4. Long myNewColumn;




6. //Java code below....

In the example above, you'll see I just injected my sql I want as that column name and the rest JPA handles for you. Other examples include:

1. @Column(name="myFunc(a)", insertable=false, updatable=false)


2. String functionResult;




4. @Column(name="select count(*) from other_table where id = a", insertable=false, updateable = false)


5. String queryResult;