Question

In my interface I have following defined

List<IFoo> GetListOfFoo<T>(Expression<Func<T, bool>> predicate) where T : IFoo;

In my implementation I’ll cast the expression in the specific type:

if (typeof(T) == typeof(Foo))
{
    Expression converted = Expression.Convert(predicate.Body, typeof(Foo));
    Expression<Func<Foo, bool>> newPredicate = 
        Expression.Lambda<Func<Foo, bool>>(converted, predicate.Parameters);
}

I try to use my implementation like this:

Expression<Func<Foo, bool>> predicate = c => c.Name == "Myname";
_repository.GetListOfFoo<Foo>(predicate);

I get no compiling errors, but if I use this, I get an Exception that in the ExpressionBody is the bool argument defined.

Where is my problem?

Answer 1

I found a better solution. I don’t need to cast the predicate themselves.

public List<IFoo> GetFoos<T>(Expression<Func<T, bool>> predicate) where T : class, IModel 
{
    var result = new List<IFoo>();
    var repository = new Repository<T>();
    result.AddRange(repository.GetEntities(predicate).ToList().ConvertAll(c => (IFoo)c));
    return result;
}