R – NHibernate – problems with validation and transactions

nhibernatetransactionsvalidation

I'm using NHibernate as my ORM. I have a situation where I have some stuff wrapped in an ITransaction. I am listening to the SaveUpdate event in NHibernate and then doing my entity validation in that SaveUpdate handler.

For one of my entities, I want to validate that the value of a certain property hasn't changed. So I figured that I would load up the value of the existing object from the database and compare it with the new value. The problem is that I called ITransaction.Commit() to save my entity object and the transaction hasn't actually been committed at the time that validation occurs, so I can't load the existing object from the database because the transaction has it locked.

So I guess I have a few different questions here:
– Is the SaveUpdate event the correct place to do validation?
– Is there another way I can do this so that I can do the validation that I need to do (getting the existing value from the database and comparing)?

I'm sure someone else out there has run into a similar situation…… hopefully!

Best Answer

Validation has nothing to do with persistence, so saveupdate is not the right place. The correct place of validation depends on: what you want to validate, your programming style, the UI framework you use to show the validation messages, etc. Personally, I prefer to put the validation on the place where things are changed, so I would put it in the change method that sets the property. I don't understand why you want to load the entity in the previous state, because that state is already loaded when you load it for the first time.

Related Solutions

R – NHibernate Rollback w/ broken rules (validation best practice)

I'm not familiar with the enterprise validation block, but can't you write an interceptor or something like that which can be used to determine whether the object can be saved or not, based on the information you have regarding the broken rules ?

You can also choose not to use the automatic dirty checking of NHibernate.
This means that you'll have to call 'Save' yourself on an object you have modified in order to get that object saved. You can get this functionality via NH Addins

NHibernate, transactions and TransactionScope

I took a very similar approach. In the HttpModule I ask the sessionfactory for a new session + bind it when a new request comes in. But I also begin the transaction here. Then when the request is ending I simply unbind it and attempt to commit the transaction.

Also my base repository doesn't take a session in any way - it instead will ask for the current session and then perform some work with the session. Also I don't wrap anything inside this base class with a transaction. Instead the entire http request is a single unit of work.

This might not be appropriate for the project you are working on, but I prefer this approach because each request will fail or succeed as a single atomic unit. I have a full blog post here with source code if you are interested in the actual implementation.

The below is a sample of what this base repository looks like:

public abstract class NHibernateRepository<T> where T : class
{

    protected readonly ISessionBuilder mSessionBuilder;

    public NHibernateRepository()
    {
        mSessionBuilder = SessionBuilderFactory.CurrentBuilder;
    }

    public T Retrieve(int id)
    {
            ISession session = GetSession();

            return session.Get<T>(id);
    }

    public void Save(T entity)
    {
            ISession session = GetSession();

            session.SaveOrUpdate(entity);
    }

    public void Delete(T entity)
    {
            ISession session = GetSession();

            session.Delete(entity);
    }

    public IQueryable<T> RetrieveAll() 
    { 
            ISession session = GetSession();

            var query = from Item in session.Linq<T>() select Item; 

            return query; 
    }

    protected virtual ISession GetSession()
    {
        return mSessionBuilder.CurrentSession;
    }
}

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