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

Question

I am trying to populate a GridView using Entity Frameworkm but every time I am getting the following error:

"Property accessor 'LoanProduct' on object 'COSIS_DAL.MemberLoan' threw the following exception: The ObjectContext instance has been disposed and can no longer be used for operations that require a connection."

My code is:

public List<MemberLoan> GetAllMembersForLoan(string keyword)
{
    using (CosisEntities db = new CosisEntities())
    {
        IQueryable<MemberLoan> query = db.MemberLoans.OrderByDescending(m => m.LoanDate);
        if (!string.IsNullOrEmpty(keyword))
        {
            keyword = keyword.ToLower();
            query = query.Where(m =>
                  m.LoanProviderCode.Contains(keyword)
                  || m.MemNo.Contains(keyword)
                  || (!string.IsNullOrEmpty(m.LoanProduct.LoanProductName) && m.LoanProduct.LoanProductName.ToLower().Contains(keyword))
                  || m.Membership.MemName.Contains(keyword)
                  || m.GeneralMasterInformation.Description.Contains(keyword)

                  );
        }
        return query.ToList();
    }
}


protected void btnSearch_Click(object sender, ImageClickEventArgs e)
{
    string keyword = txtKeyword.Text.ToLower();
    LoanController c = new LoanController();
    List<COSIS_DAL.MemberLoan> list = new List<COSIS_DAL.MemberLoan>();
    list = c.GetAllMembersForLoan(keyword);

    if (list.Count <= 0)
    {
        lblMsg.Text = "No Records Found";
        GridView1.DataSourceID = null;
        GridView1.DataSource = null;
        GridView1.DataBind();
    }
    else
    {
        lblMsg.Text = "";
        GridView1.DataSourceID = null;   
        GridView1.DataSource = list;
        GridView1.DataBind();
    }
}

The error is mentioning the LoanProductName column of the Gridview. Mentioned: I am using C#, ASP.net, SQL-Server 2008 as back end DB.

I am quite new to Entity Framework. I can't understand why I am getting this error. Can anyone help me please?

Batt

Are you accessing any navigation properties in the gridview. If you do, you need to include those navigation tables in the query as well. Like query.Include("SomeOtherTable") – Stringer

Try either creating a proxy class to host your entity or at least return an anonymous object. From my point of view, using ef does require creating proxy classes to implement your logics, use the edmx just as the db access layer not as business. – Cyclic

yes in the gridview I am getting another table column also. Which is LoanProviderName. – Batt

Thanks for your answer Gonzix but I could not understand as I am so new in Entity framework and as well as in Linq. Can you please make me a bit more clear? – Batt

LINQ-style data sources are lazily evaluated, which means they only actually query the database when you start to read results from them. What this means is that you're attempting to read results - or read lazily-loaded properties from existing results, i.e. properties that weren't read at the point the object was initially loaded - after your database session has closed. You'll need to make sure that the initial read is done whilst the session is open (I don't know ASP.NET's controls well enough, but this ought to happen) and that any child entities you want to display are read then too. – Pikeman

Try db.MemberLoans.Include("LoanProduct").OrderByDescending() check the syntax cause I dont have VS in front of me. – Stringer

Thanks a lot Nilesh your answer was really helpful. the error has been gone but now I am having the same error for another field which comes from one more table can you please tell me how can I include another table here? Thank you – Batt

You just need to go on including all the navigation properties that you are accessing outside the context like db.MemberLoans.Include("LoanProduct").Include("SomeOtherTable). Check the answers by @Tragedian and @lazyberezovsky – Stringer

Answer 1

By default Entity Framework uses lazy-loading for navigation properties. That's why these properties should be marked as virtual - EF creates proxy class for your entity and overrides navigation properties to allow lazy-loading. E.g. if you have this entity:

public class MemberLoan
{
   public string LoandProviderCode { get; set; }
   public virtual Membership Membership { get; set; }
}

Entity Framework will return proxy inherited from this entity and provide DbContext instance to this proxy in order to allow lazy loading of membership later:

public class MemberLoanProxy : MemberLoan
{
    private CosisEntities db;
    private int membershipId;
    private Membership membership;

    public override Membership Membership 
    { 
       get 
       {
          if (membership == null)
              membership = db.Memberships.Find(membershipId);
          return membership;
       }
       set { membership = value; }
    }
}

So, entity has instance of DbContext which was used for loading entity. That's your problem. You have using block around CosisEntities usage. Which disposes context before entities are returned. When some code later tries to use lazy-loaded navigation property, it fails, because context is disposed at that moment.

To fix this behavior you can use eager loading of navigation properties which you will need later:

IQueryable<MemberLoan> query = db.MemberLoans.Include(m => m.Membership);

That will pre-load all memberships and lazy-loading will not be used. For details see Loading Related Entities article on MSDN.

Deluna

Thanks a lot for your helpful explanation and answer. Actually here I am including three table so I don't know how I can add the three tables with INCLUDE. can you please help me on this please. – Batt

@Batt just include all navigation properties one by one. E.g. db.MemberLoans.Include(m => m.Membership).Include(m => m.LoanProduct).OrderByDescending(m => m.LoanDate); that will generate JOIN query and return all data at once. – Deluna

Thanks mate, perfect. I had a using statement that was limiting the lazy loading. Great answer. – Harilda

@Batt An easy way to prevent accidentally Lazy Loading things is to turn it off with Configuration.LazyLoadingEnabled = false; in the constructor of your DbContext. Lazy Loading can have serious performance issues in some cases, so I usually turn it off by default. This forces you to explicitly load any navigation properties, as Sergey showed. – Suttee

What if I don't want to include those related entities in my query at all? – Geri

Answer 2

The CosisEntities class is your DbContext. When you create a context in a using block, you're defining the boundaries for your data-oriented operation.

In your code, you're trying to emit the result of a query from a method and then end the context within the method. The operation you pass the result to then tries to access the entities in order to populate the grid view. Somewhere in the process of binding to the grid, a lazy-loaded property is being accessed and Entity Framework is trying to perform a lookup to obtain the values. It fails, because the associated context has already ended.

You have two problems:

1. You're lazy-loading entities when you bind to the grid. This means that you're doing lots of separate query operations to SQL Server, which are going to slow everything down. You can fix this issue by either making the related properties eager-loaded by default, or asking Entity Framework to include them in the results of this query by using the Include extension method.

2. You're ending your context prematurely: a DbContext should be available throughout the unit of work being performed, only disposing it when you're done with the work at hand. In the case of ASP.NET, a unit of work is typically the HTTP request being handled.

Shagbark

Answer 3

Bottom Line

Your code has retrieved data (entities) via entity-framework with lazy-loading enabled and after the DbContext has been disposed, your code is referencing properties (related/relationship/navigation entities) that was not explicitly requested.

More Specifically

The InvalidOperationException with this message always means the same thing: you are requesting data (entities) from entity-framework after the DbContext has been disposed.

A simple case:

(these classes will be used for all examples in this answer, and assume all navigation properties have been configured correctly and have associated tables in the database)

public class Person
{
  public int Id { get; set; }
  public string name { get; set; }
  public int? PetId { get; set; }
  public Pet Pet { get; set; }
}

public class Pet 
{
  public string name { get; set; }
}

using (var db = new dbContext())
{
  var person = db.Persons.FirstOrDefaultAsync(p => p.id == 1);
}

Console.WriteLine(person.Pet.Name);

The last line will throw the InvalidOperationException because the dbContext has not disabled lazy-loading and the code is accessing the Pet navigation property after the Context has been disposed by the using statement.

Debugging

How do you find the source of this exception? Apart from looking at the exception itself, which will be thrown exactly at the location where it occurs, the general rules of debugging in Visual Studio apply: place strategic breakpoints and inspect your variables, either by hovering the mouse over their names, opening a (Quick)Watch window or using the various debugging panels like Locals and Autos.

If you want to find out where the reference is or isn't set, right-click its name and select "Find All References". You can then place a breakpoint at every location that requests data, and run your program with the debugger attached. Every time the debugger breaks on such a breakpoint, you need to determine whether your navigation property should have been populated or if the data requested is necessary.

Ways to Avoid

Disable Lazy-Loading

public class MyDbContext : DbContext
{
  public MyDbContext()
  {
    this.Configuration.LazyLoadingEnabled = false;
  }
}

Pros: Instead of throwing the InvalidOperationException the property will be null. Accessing properties of null or attempting to change the properties of this property will throw a NullReferenceException.

How to explicitly request the object when needed:

using (var db = new dbContext())
{
  var person = db.Persons
    .Include(p => p.Pet)
    .FirstOrDefaultAsync(p => p.id == 1);
}
Console.WriteLine(person.Pet.Name);  // No Exception Thrown

In the previous example, Entity Framework will materialize the Pet in addition to the Person. This can be advantageous because it’s a single call the the database. (However, there can also be huge performance problems depending on the number of returned results and the number of navigation properties requested, in this instance, there would be no performance penalty because both instances are only a single record and a single join).

or

using (var db = new dbContext())
{
  var person = db.Persons.FirstOrDefaultAsync(p => p.id == 1);

  var pet = db.Pets.FirstOrDefaultAsync(p => p.id == person.PetId);
}
Console.WriteLine(person.Pet.Name);  // No Exception Thrown

In the previous example, Entity Framework will materialize the Pet independently of the Person by making an additional call to the database. By default, Entity Framework tracks objects it has retrieved from the database and if it finds navigation properties that match it will auto-magically populate these entities. In this instance because the PetId on the Person object matches the Pet.Id, Entity Framework will assign the Person.Pet to the Pet value retrieved, before the value is assigned to the pet variable.

I always recommend this approach as it forces programmers to understand when and how code is request data via Entity Framework. When code throws a null reference exception on a property of an entity, you can almost always be sure you have not explicitly requested that data.

Unconscious

Answer 4

It's a very late answer but I resolved the issue turning off the lazy loading:

db.Configuration.LazyLoadingEnabled = false;

Enlistee

Downside is you have to use .Include and things like that to load navigation properties. – Hecto

Answer 5

If you're using ASP.NET Core and wonder why you get this message in one of your async controller methods, make sure you return a Task rather than void - ASP.NET Core disposes injected contexts.

(I'm posting this answer as this question is high in the search results to that exception message and it's a subtle issue - maybe it's useful to people who Google for it.)

Immoderacy

Answer 6

In my case, I was passsing all models 'Users' to column and it wasn't mapped correctly, so I just passed 'Users.Name' and it fixed it.

var data = db.ApplicationTranceLogs 
             .Include(q=>q.Users)
             .Include(q => q.LookupItems) 
             .Select(q => new { Id = q.Id, FormatDate = q.Date.ToString("yyyy/MM/dd"), ***Users = q.Users,*** ProcessType = q.ProcessType, CoreProcessId = q.CoreProcessId, Data = q.Data }) 
             .ToList();

var data = db.ApplicationTranceLogs 
             .Include(q=>q.Users).Include(q => q.LookupItems) 
             .Select(q => new { Id = q.Id, FormatDate = q.Date.ToString("yyyy/MM/dd"), ***Users = q.Users.Name***, ProcessType = q.ProcessType, CoreProcessId = q.CoreProcessId, Data = q.Data }) 
             .ToList();

Justifiable

Answer 7

Most of the other answers point to eager loading, but I found another solution.

In my case I had an EF object InventoryItem with a collection of InvActivity child objects.

class InventoryItem {
...
   // EF code first declaration of a cross table relationship
   public virtual List<InvActivity> ItemsActivity { get; set; }

   public GetLatestActivity()
   {
       return ItemActivity?.OrderByDescending(x => x.DateEntered).SingleOrDefault();
   }
...
}

And since I was pulling from the child object collection instead of a context query (with IQueryable), the Include() function was not available to implement eager loading. So instead my solution was to create a context from where I utilized GetLatestActivity() and attach() the returned object:

using (DBContext ctx = new DBContext())
{
    var latestAct = _item.GetLatestActivity();

    // attach the Entity object back to a usable database context
    ctx.InventoryActivity.Attach(latestAct);

    // your code that would make use of the latestAct's lazy loading
    // ie   latestAct.lazyLoadedChild.name = "foo";
}

Thus you aren't stuck with eager loading.

Sublet

This is basically eager loading, you've loaded the object via a context. There is only two options; eager loading and lazy loading. – Unconscious

@ErikPhilips right, it's lazy loading with a new data context – Sublet

@ErikPhilips - there is also Explicit Loading - learn.microsoft.com/en-us/ef/ef6/querying/… – Crump

Answer 8

Could be

 -> context.Configuration.ProxyCreationEnabled = false;

using (var context = new BDPuntoDeVenta())
            {
                context.Configuration.ProxyCreationEnabled = false;
                return context.FacturaDetalle.Where(x => x.ID_Factura == _ID_Factura && x.Devuelto != true).ToList();
            }

Ebby

There are two other answers which directly suggest this. – Deontology