Question

I have the following LINQ query:

var query = session.Query<Event>()
    .Fetch(e => e.Venue); // Fetch is an IQueryable extension which does a join

// Code needed here to remove the fetch part

var num = query.Count(); // This then hits the database

Unfortunately this throws an error as fetch is not supported for a count method. At this stage i’m sure you’re thinking why don’t i remove the fetch part. However i have simplified my example and this is not possible. What i’d ideally like to be able to do is navigate the expression tree for the LINQ query and remove any calls to Fetch before i call Count.

I’d appreciate it if someone could show how this is possible. Thanks

Answer 1

It is possible to change expression trees at runtime (by building a new one out of the existing one), since O/RM tools such as LINQ to SQL and Entity Framework do this constantly, but it’s not really easy. It has become easier with the introduction of the ExpressionVisitor class of .NET 4.0, but still don’t expect it to be simple.

Here is an article that shows an example of this.