实体框架6-上下文返回的列表的某些对象具有空属性

Question

I am retrieving a list of entities like this :

var traductions = from t in context.Traductions
                        where t.User.ID == user.ID
                        && (DateTime.Now < t.EndDate)
                        select t;

var list = traductions.ToList();

Here is the model :

Here is the first class :

    public class Original
    {
    public int ID { get; set; }
    public string Name { get; private set; }
    public Traduction Traduction { get; private set; }
    }

And here is the second class :

   public class Traduction
   { 
    public int ID { get; set; }
    public Original Original { get; private set; }
    public string Content { get; private set; }
   }

I get 4 entities - that's good - however one of the properties of some of my retrieved objects is null - Original. In 3 of the 4 object the Original property is null, but this property is correctly populated in the 4th. I have checked in the Database directly and the Primary Keys / FK are consistent.

What do you think about it? I don't understand because normally if there is a problem this property should be null for all the retrieved objects, but here the property is correctly populated for one of the objects.

Thanks

Answer 1

My first thought is you might have a circular reference. Is it possible to have a Traduction, that contains an Original that contains the first Traduction? If you do that could be what you're seeing. You'll definitely have problems if/when you try to serialize things.

The following won't help a circular reference, but could be why the data is not loading as you'd expect.

You could try using lazy loading. To do that you'll use the 'virtual' keyword in your classes like:

public class Original
{
    public int ID { get; set; }
    public string Name { get; private set; }
    public virtual Traduction Traduction { get; private set; }
}

public class Traduction
{ 
    public int ID { get; set; }
    public virtual Original Original { get; private set; }
    public string Content { get; private set; }
}

Or you can specifically include the objects in your query:

var traductions = from t in context.Traductions.Include("Original")
                  where t.User.ID == user.ID
                  && (DateTime.Now < t.EndDate)
                  select t;