Question

More specifically in Raven DB, I want to create a generic method with a signature like;

public void Clear<T>() {...

Then have Raven DB clear all documents of the given type.

I understand from other posts by Ayende to similar questions that you’d need an index in place to do this as a batch.

I think this would involve creating an index that maps each document type – this seems like a lot of work.

Does anyone know an efficient way of creating a method like the above that will do a set delete directly in the database?

Answer 1

After much experimentation I found the answer to be quite simple, although far from obvious;

public void Clear<T>()
{
    session.Advanced.DocumentStore.DatabaseCommands.PutIndex(indexName, new IndexDefinitionBuilder<T>
    {
        Map = documents => documents.Select(entity => new {})
    });

    session.Advanced.DatabaseCommands.DeleteByIndex(indexName, new IndexQuery());
}

Of course you almost certainly wouldn’t define your index and do your delete in one go, I’ve put this as a single method for the sake of brevity.

My own implementation defines the indexes on application start as recommended by the documentation.

If you wanted to use this approach to actually index a property of T then you would need to constrain T. For example if I have an IEntity that all my document classes inherit from and this class specifies a property Id. Then a ‘where T : IEntity’ would allow you to use that property in the index.

It’s been said in other places, but it’s also worth noting that once you define a static index Raven will probably use it, this can cause your queries to seemingly not return data that you’ve inserted:

RavenDB Saving to disk query