Hibernate：在删除之前检查外键约束违规？

Question

The system I'm currently working on has a policy in which objects that have no relationships can be freely deleted, while those that do must be logically deleted. This is meant to prevent historical information from being deleted.

So basically, what I was trying to do was determine whether an object's key is currently present in another table. If it isn't I would simply call delete(), otherwise I would set a property that indicates a logical delete, and call update().

I'm using Spring transaction management, so I'm trying to mess with the session itself as least as possible. My initial approach seemed to work at first, but you'll see that it has a major flaw:

@Transactional
public void deleteObject(SomeEntity object)
{       
    //try to delete
    this.someEntityDAO.delete(object);

    try //force foreign key constraint check
    {
        this.someEntityDAO.flush();
    }
    catch (ConstraintViolationException e)
    {
        //reload object
        object= this.someEntityDAO.loadById(object.getId());

        //save as inactive instead of deleting
        object.setActive(false);
        this.someEntityDAO.update(object);
    }
}

Since Hibernate exceptions are fatal, this is completely unreliable (even though it works). I was wondering if there is a way to do a sort of "peek" operation in which I could test if the delete will fail due to a constraint, without actually performing the operation (and thus invalidating the session). The only thing I can think of is to manually check each related table to see if the id is present, but this would be very tedious and error-prone in tables with many relationships. I want to leverage the constraints that are already in place in the database, if possible.

Answer 1

Speaking specifically to:

So basically, what I was trying to do was determine whether an object's key is currently present in another table. If it isn't I would simply call delete(), otherwise I would set a property that indicates a logical delete, and call update().

and:

I was wondering if there is a way to do a sort of "peek" operation in which I could test if the delete will fail due to a constraint, without actually performing the operation (and thus invalidating the session).

I have only worked occasionally with Hibernate, but the general answer is: This is what SQL is for. It's all in your where clause!

For clarity: You do your delete with a sufficient where clause that it does the check in the transaction itself; The delete deletes whatever it is that meets the constraints given.

Update:

When you write:

"So basically, what I was trying to do was determine whether an object's key is currently present in another table. If it isn't I would simply call delete(), otherwise I would set a property that indicates a logical delete, and call update()."

the problem is that YOU are trying to do this when you should let (direct) the database engine to do it for you in your SQL. Investigate use of the "not exists" clause...