Extending LINQ to Nhibernate provider, in combination with Dynamic LINQ problem

Question

I\'m using NHibernate 3.1.0 and I\'m trying to extend the LINQ provider by using BaseHqlGeneratorForMethod and extending the DefaultLinqToHqlGeneratorsReg

Answer 1

I had the same problem and fixed it.
At first I want to thank murki for providing the information which got me on my way!

The answer lies partly in Fabio's post. To solve this issue you have to use the RegisterGenerator instead of the Merge method in the CustomLinqToHqlGeneratorsRegistry constructor. My implementation of the CustomLinqToHqlGeneratorsRegistry class is as follows:

public class CustomLinqToHqlGeneratorsRegistry : DefaultLinqToHqlGeneratorsRegistry
{
    public CustomLinqToHqlGeneratorsRegistry()
        : base()
    {
        MethodInfo toStringMethod = ReflectionHelper.GetMethodDefinition<int>(x => x.ToString());
        RegisterGenerator(toStringMethod, new ToStringGenerator());
    }
}

Answer 2

Supposing the property Id of the class Project it's an Int32 try registering the corresponding Int32.ToString() method in your ToStringGenerator class.

...
public ToStringGenerator()
{
    SupportedMethods = new[]
        {
            ReflectionHelper.GetMethodDefinition<object>(x => x.ToString()),
            ReflectionHelper.GetMethodDefinition<int>(x => x.ToString()),
        };
}
...

Answer 3

There are two, well defined, separate stages here:

1. Converting the dynamic (string) query into a static expression (done by the Dynamic Linq library)
2. Parsing that into an HqlTree, then executing (done by NHibernate)

Since you have determined that a static expression works well, the problem lies in 1.

What happens if you do the following?

var results = Enumerable.Empty<Project>().AsQueryable();
string pId = "1";
results = results.Where("Id.ToString().Contains(@0)", pId);

If it fails, you'll have confirmed it's a problem with Dynamic Linq alone (i.e. it doesn't support the expression you're feeding it), so you'll have to dig into it and patch it.

Semi-related: the ToStringGenerator looks useful; could you submit a patch for NHibernate? http://jira.nhforge.org