I tried to find an easy way of deleting/updating entities directly in LLBLGen, and the methods DeleteEntitiesDirectly/UpdateEntitiesDirectly seem the perfect match for what I need. However, it would be way easier to use something like:

adapter.DeleteEntitiesDirectly<Customer>(c => c.Name.StartsWith("John"));

instead of manually creating the predicate bucket. Did I miss something or these LINQ expressions are not supported currently?

This is not available. I'll pass your request to the developing team.

Parsing expression trees is pretty complicated, as there's no end to what you can add there: you can specify a complicated expression there spanning a lot of entities. Parsing expression trees in our linq provider is a complicated process which isn't re-usable here, hence we don't offer that.

It's not all bad tho. The QuerySpec extension methods make specifying the predicates not that complicated.

adapter.DeleteEntitiesDirectly(new RelationPredicateBucket(CustomerFields.Name.Equal("John")));

If you hate the bucket ctor call, you can add an extension method, e.g. ToBucket(IPredicate) :

public static IRelationPredicateBucket(this IPredicate toWrap)
{
    return new RelationPredicateBucket(toWrap);
}

Which then leads to:

adapter.DeleteEntitiesDirectly(CustomerFields.Name.Equal("John").ToBucket());

@Otis: thanks for the clarification. It would have been very nice to have a syntax not so dependent on LLBLGen, like LINQ is, but I understand the difficulties. At least I know what I can do .