How can I share object level logic across Entity Framework queries?

Question

I am looking to share some very simple logic across multiple queries in Entity Framework. Say I have the following models

public class User
{
    // user properties
    public ICollection<UserRole> Roles { get; set; }
}

public class UserRole : IDateRestricted
{
    public RoleType Type { get; set; }
    public DateTime StartDate { get; set; }
    public DateTime? EndDate { get; set; }
}

public interface IDateRestricted
{
    DateTime StartDate { get; set; }
    DateTime? EndDate { get; set; }
}

If I was using normal LINQ I could create a simple extension method that would allow me to determine if the role was currently active.

public static class DateRestrictedExtensions
{
    public static Boolean IsActive(this IDateRestricted entity)
    {
        return entity.StartDate <= DateTime.Now && (entity.EndDate == null || entity.EndDate > DateTime.Now);
    }
}

and I could use it like so.

var admins = users.Where(x => x.Roles.Any(role => role.Type == RoleType.Admin && role.IsActive()));

With entity framework this fails with the dreaded:

LINQ to Entities does not recognize the method Boolean IsActive(Domain.Interfaces.IDateRestricted) method, and this method cannot be translated into a store expression.

Is there a way that I can share this logic and have LINQ to Entities support it when querying?

You could also create extensions that return Expression<Func> types but you would need to pass them as the whole parameter of the e.g. Any. — NetMage
– NetMage, Commented Jun 12, 2018 at 23:31

Slava Utesinov · Accepted Answer · 2018-06-14 10:30:35Z

1

You should use Expression<Func<IDateRestricted, bool>> instead of Func<IDateRestricted, bool> - presented exception's description exactly points to it:

public static class DateRestrictedExtensions
{
    public static Expression<Func<IDateRestricted, bool>> IsActive()
    {
        return entity => entity.StartDate <= DateTime.Now 
                         && (entity.EndDate == null || entity.EndDate > DateTime.Now);
    }
}

var admins = users.Where(x => x.Roles.AsQueryable().Where(role.Type == RoleType.Admin)
                                   .Any(DateRestrictedExtensions.IsActive()));

edited Jun 14, 2018 at 10:30

answered Jun 13, 2018 at 5:49

Slava Utesinov

13.5k2 gold badges21 silver badges26 bronze badges

Sign up to request clarification or add additional context in comments.

5 Comments

Aaron Roberts Over a year ago

Thought about this but the .Any() method does not accept an expression it would seem

Aaron Roberts Over a year ago

Adding .AsQueryable() to the roles collection allows it to work. Also you must include the static class name in the method call. If you update the answer with these I will accept it.

Slava Utesinov Over a year ago

@AaronRoberts, can you explain, why it is not working without .AsQueryable(). What problem did you face?

Aaron Roberts Over a year ago

there is no error because it doesn’t build. The LINQ extension methods on an ICollection don’t accept expression functions as a parameter.

Slava Utesinov Over a year ago

@AaronRoberts, yes, indeed, fixed.

Collectives™ on Stack Overflow

How can I share object level logic across Entity Framework queries?

1 Answer 1

5 Comments

Your Answer

Hot Network Questions

Collectives™ on Stack Overflow

1 Answer 1

5 Comments

Your Answer

Sign up or log in

Post as a guest

Related