QueryOver error : Unrecognised method call in expression value

问题

I have a query by QueryOver in Nhibernate3.1

 var q = SessionInstance.QueryOver<Person>()
         .Where(x => IsActive(x.PersonType) == true);

 return q.List<Person>();

By this method:

private bool IsActive(PersonType type)
{
   if(type == PersonType.Employee
      return true;
   else
      return false;
}

Now it has a runtime error by this message:

Unrecognised method call in expression value

Why?

回答1:

I solved a similar problem by returning an expression tree in my predicate method instead of returning a boolean value directly. Using your example, it'd be something like this:

private Expression<Func<PersonType, bool>> IsActive()
{
    return (t => t == PersonType.Employee );
}

回答2:

Your Method IsActive is a method compiled directly to IL. The query analyzer cant dissect this method and build a query out of it. I'm not sure how you can expose an expression from a method and use it in a query with NHibernate but i'm sure google can help you with that.

回答3:

Can you not just do this?

var q = SessionInstance.QueryOver<Person>()
         .Where(x => x.PersonType == PersonType.Employee);

来源：https://stackoverflow.com/questions/9377774/queryover-error-unrecognised-method-call-in-expression-value