JPA @version - can it be used to calcualate version of a table entry
Please consider the following table (created using a corresponding entity)
request
-------
id requestor type version items
1 a t1 1 5
2 a t1 2 3
3 b t1 1 2
4 a t2 1 4
5 a t1 3 9
The above is what I want to achieve. The version field is a calculated field others are user provided. Basically the request's version needs to be calculated based on the combination of requestor and the type. The first occurance with a given combination will have a version 1 then version 2 and so on.
I tried various things using @version on a different entity with just the three columns and joining the two entities using ManytoOne etc but I'm not able to get to the desired outcome. I dont want to confuse you with the things I tried.
Since the objective is simple there should be an easier way I suppose? Can you please help? - any help gr开发者_运维技巧eatly appreciated!
thanks in advance
The Version
annotation is used to specify the version field or property of an entity class that serves as its optimistic lock value. I don't think this has anything to do with what you're looking for. Here are some ideas though:
- Use a trigger on insert.
- Use a SQL View.
- Use a provider specific extension for derived attributes like Hibernate's
@Formula
(this annotation that lets you map a property to an SQL expression rather than a table column).
To illustrate the latest option, you could declare something like this:
@Formula("(select count(r.id)+1 from Request r where r.requestor=requestor and r.type=type and r.id<id)")
public long getVersion() { return version; }
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