How can I check if my Entity object is lazy loading?

Question

I have two entity classes that have a one-to-many relationship.

public class Call : IEntity
{
    public int Id { get; set; }
    public int UserId { get; set; }
    public virtual User User { get; set; }
}

public class User : IEntity
{
    public int Id { get; set; }

    public string Username { get; set; }
    public virtual ICollection<Call> Calls { get; set; }
}

And I have a view model for 'Call' operations on the web layer.

public class CallVm : IViewModel
{
    public string Id { get; set; }
    public string UserFullname { get; set; }
}

And I use a method to convert my 'Call' object to 'CallVm' object. This method is briefly as follows.

public CallVm MapCallVm(Call call)
{
    return call == null ? null : new CallVm { Id = call.Id, UserFullname = call.User?.Fullname };
}

When I read the 'Call' entity from the database, I sometimes include 'User' and sometimes I don't. When I do not include it, there is no User property definition in the Call object because it is lazy loading. Therefore, I get the following error in MapCallVm method.

The ObjectContext instance has been disposed and can no longer be used for operations that require a connection.

Is there a way to check this? I just want to assign UserFullname = call.User?.Fullname when there is a eager load. The only solution I can think of is controlling with try-catch. Is there a different solution?

you could disable lazy loading then you would know as it will throw an exception. — Seabizkit
– Seabizkit, Commented Feb 5, 2020 at 7:01

Nguyễn Văn Phong · Accepted Answer · 2020-02-05 06:51:40Z

2

You can use DbReferenceEntry.IsLoaded Property.

Gets or sets a value indicating whether the entity has been loaded from the database.

if (_dbContext.Entry(Call).Reference(e => e.User).IsLoaded)

Updated

If you are getting value without dbContext, you should force the query to Eager loading instead.

Read the following post to have a better understanding.

Should we disable lazy loading of Entity Framework in web apps?

edited Feb 5, 2020 at 6:51

answered Feb 5, 2020 at 5:59

Nguyễn Văn Phong

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5 Comments

user12843193 Over a year ago

I do not have access to the dbContext object in 'MapCallVm' method. I need to do this control without mixing the context class. Can't I control it directly over the 'Call' object? For this I wrote a code like this:

user12843193 Over a year ago

public CallVm MapCallVm(Call call)             {                 string userFullName;                 try { userFullName = call.User?.Username; }                 catch { userFullName = null; }                 return call == null ? null : new CallVm { Id = HashidsHelper.Encrypt(call.Id), ContactId = HashidsHelper.Encrypt(call.ContactId), UserFullname = userFullName, IsAccess = call.IsAccess, Date = call.Date };             }

Nguyễn Văn Phong Over a year ago

If you are getting value without dbContext, you should force the query to Eager loading instead. Anyway, your code is okie. But It's not a good way.

Nguyễn Văn Phong Over a year ago

You should read this link to have a better understanding.

Aleksej Vasinov Over a year ago

Phong is right - try to avoid passing database entities to your views

Nguyễn Văn Phong · Accepted Answer · 2020-02-06 01:04:21Z

As @Phong's answer - avoid passing DbContext. Normally, your repository class should map DB entities to simple POCO/DTO objects.

I suggest to introduce mapper class. This will help you to unit test your logic

// Interface to inject to repository
public interface ICallMapper
{
    CallVm Map(Call call);
}

public class CallMapper : ICallMapper
{
    public CallVm Map(Call call)
    {
        return call == null ? null : new CallVm { Id = call.Id, UserFullname = call.User?.Username };
    }
}

Pass mapper to repository and ensure that your objects are not connected with DB anymore

public class CallRepository : ICallRepository
{
    private readonly ICallMapper _callMapper;

    public CallRepository(ICallMapper callMapper)
    {
        _callMapper = callMapper;
    }

    public IList<CallVm> GetList()
    {
        // Call DB and get entities
        var calls = GetCalls();

        // Map DB entities to plain model
        return calls.Select(_callMapper.Map).ToList();
    }
}

This lets you to get rid of your error. And makes your program more structable and testable.

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