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

Question

In various database tables I have both a property and a value column. I\'m using Linq to SQL to access the database.

I\'m writing a method which returns a dictionary

Answer 1

This happens because of how Table is declared:

public sealed class Table : IQueryable, 
    IQueryProvider, IEnumerable, ITable, IQueryable, IEnumerable, 
    IListSource
where TEntity : class  // <-- T must be a reference type!

The compiler is complaining because your method has no constraints on T, which means that you could accept a T which doesn't conform to the specification of Table.

Thus, your method needs to be at least as strict about what it accepts. Try this instead:

private static Dictionary GetProperties(Table table) where T : class