How to make a method generic when "type 'T' must be a reference type"? [duplicate]

Question

Possible Duplicate:
Why do I get “error: … must be a reference type” in my C# generic method?

I have 2 Repository methods that are almost identical:

public IList<Fund> GetFundsByName(int pageSize, string searchExpression) {     return _session.CreateCriteria<Fund>()         .AddNameSearchCriteria<Fund>(searchExpression)         .AddOrder<Fund>(f => f.Name, Order.Asc)         .SetMaxResults(pageSize).List<Fund>(); }  public IList<Company> GetCompaniesByName(int pageSize, string searchExpression) {     return _session.CreateCriteria<Company>()         .AddNameSearchCriteria<Company>(searchExpression)         .AddOrder<Company>(f => f.Name, Order.Asc)         .SetMaxResults(pageSize).List<Company>(); } 

The only difference is that the first one's _session.CreateCriteria is of type Fund and the second one is company

I was hoping that I could make this generic by changing the method definition to:

public IList<T> GetEntitiesByName<T>(int pageSize, string searchExpression)     where T : ISearchableEntity {     return _session.CreateCriteria<T>()         .AddNameSearchCriteria<T>(searchExpression)         .AddOrder<T>(f => f.Name, Order.Asc)         .SetMaxResults(pageSize).List<T>(); } 

where ISearchableEntity is defined as:

public interface ISearchableEntity {     string Name { get; set; } } 

but unfortunately NHibernate doesn't like this and gives me the error:

The type 'T' must be a reference type in order to use it as parameter 'T' in the generic type or method 'NHibernate.ISession.CreateCriteria<T>()'

Is it possible for me to make this generic some other way?

Answer 1

You could try adding the constraint class:

where T : class, ISearchableEntity 

Answer 2

Here's the full list of constraints you can use on T

http://msdn.microsoft.com/en-us/library/d5x73970.aspx