Hibernate - Insert Before Delete
Today I faced a problem that I already had faced some time before, but I didn’t documented that in blog entry or even in my “ProblemsThatCanNotBeForgotten.TXT”. So that’s the time for that.
The problem is: I have an entity called Team who has a List of Players (other entity). I’m trying to move an Player from one team to the other at the same transaction. Follow some code:
After load this Entity by the JPA/Hibernate engine and have the tables created this is the structure and the indexes created:
The Problem
As happens in the real world some teams wants to trade their players, so the software has to be able to transfer one player from one team to another.
The code wich do this is very simple, just remove a player from one collection’s player team from the seller team and then insert the remove player to the buyer team.
After the transfer, the application apply this changes on the Database with merge(entity) call.
Doing this a message telling that it’s impossible to insert a duplicate row blows up on the console.
This is because Hibernate does the INSERT statement BEFORE the DELETE.
After looking at Internet I didn’t find anything to solve that. Just a workaround that fixes that. But as I said, it’s a workaround.
Solving (woking it around)
To solve that problem I changed the reference from Team to Player from @OneToMany to @ManyToMany. The problem with this approach is that I lose the rule in the DB that has the control over the unicity of a player belonging to just one Team.
This is how the code and the table at the DB look like:
