Question

I’ve added a custom property to a LINQ-to-SQL entity:

public partial class User
{
    public bool IsActive
    {
        get
        {
            // note that startDate and endDate are columns of User table
            return startDate <= DateTime.Now && endDate >= DateTime.Now;
        }
    }
}

and now I need to use this property with lambda expressions:

activeUsers = users.Where(u => u.IsActive);

but when this code is executed I get a System.NotSupportedException. The exception message says that “SQL conversions for the member ‘User.IsActive’ are not supported”.

Is there a way to solve this problem?

Answer 1

The IsActive you show is regular C# – it will be compiled to IL and will not be available for LINQ-to-SQL (etc) to inspect and turn into TSQL to execute at the database. One option here might be:

public static Expression<Func<User,bool>> GetIsActiveFilter() {
    return user => user.StartDate <= DateTime.Now &&
                   user.EndDate >= DateTime.Now;
}

then you should be able to use:

activeUsers = users.Where(User.GetIsActiveFilter());

Or similarly – maybe an extension method:

public static IQueryable<User> ActiveOnly(this IQueryable<User> users) {
    return users.Where(user => user.StartDate <= DateTime.Now &&
                               user.EndDate >= DateTime.Now);
}

then:

activeUsers = users.ActiveOnly();

The difference here is that we are using the IQueryable<T> interface and expression trees throughout, which allows LINQ to understand our intent, and create suitable TSQL to achieve the same.