Is it possible to query on an interface property?

Question

I have the following class:

public class BicycleSellerListing : IUserName
{
    public UserProfile UserProfile { get; set; }

    /// <summary>
    /// IUserName interface property
    /// </summary>
    public string UserName
    {
        get
        {
            return UserProfile.UserName;
        }
    }
}

The interface:

public interface IUserName
{
    string UserName { get; }
}

And this query:

public static List<T> GetList<T>(string userName) where T : class, IUserName
{
    using (SqlUnitOfWork work = new SqlUnitOfWork())
    {
        return work.GetList<T>(row => row.UserName == userName)
            .ToList();
    }
}

When I execute this query, I get the following exception:

The specified type member 'UserName' is not supported in LINQ to Entities. Only initializers, entity members, and entity navigation properties are supported.

I understand why I'm getting the exception, but am wondering if there is a way I can perform this query using the interface?

score 2 · Accepted Answer · edited May 23 '17 at 10:25

2

To answer you quistion:

Is it possible to query on an interface property?

Yes. it's no problem. The fault you are getting is not becuase of the interface.

The problem is that you can't query on properties that isn't mappe with Linq 2 Entities

Other people have had this propblem as well.

The underlying expressionbuilder can not distinct between properties that is mapped to the database, and properties that is not.

It is a problem becuase the compiler can't help you. In Linq to object, it is no problem, so the compiler doesnt throw any errors/warnings

You should try to make it clear the this property is not mapped - perhaps by a prefix, or a nested class that contains all the "custom" properties.

edited May 23 '17 at 10:25

Community

1
1

answered Mar 15 '13 at 12:07

Jens Kloster

11,099
5
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That's the case. The error message already states it: `entity members`. `UserName` is not part of the model, and therefor is not an `entity member`. – JustAnotherUserYouMayKnow Mar 15 '13 at 12:08
I suspect I can. Will have to get back to a desk to test this out. – Aron Mar 15 '13 at 16:12

score 0 · Answer 2 · answered Mar 15 '13 at 12:13

0

In addition to the existing answer(s), you can perform the where in memory, but that means retrieving the whole table.

Normally I wouldn't recommend this though.

public static List<T> GetList<T>(string userName) where T : class, IUserName
{
    using (SqlUnitOfWork work = new SqlUnitOfWork())
    {
        return work.GetList<T>()
            .AsEnumerable()
            .Where(row => row.UserName == userName)
            .ToList();
    }
}

answered Mar 15 '13 at 12:13

Maarten

22,527
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1

I would emphasize that this will retrieve the **entire** table. Depending on the size of this table this can be a **huge performance penalty**. – JustAnotherUserYouMayKnow Mar 15 '13 at 13:01

score 0 · Answer 3 · answered Mar 15 '13 at 14:30

Some workarounds:

You could try to determine underlying entity type in runtime and
then dynamically compile and invoke a generic method executing query with this type.
It is possible to assemble this query manually in runtime using Expression class
You could try Entity SQL query syntax instead of Linq

Is it possible to query on an interface property?

3 Answers3