c# - System.ObjectDisposedException: The ObjectContext instance has been disposed and can no longer be used for operations that require a connection

Question

I am using EF 4 to retrieve a list of Employees.

public ContentResult AutoCompleteResult(string searchText)
{
    List<Employee> list = Employee.GetAllCurrentEmployees();
    List<Employee> filteredEmployees = list
        .Where(x => x.GetName().ToLower().Contains(searchText.ToLower()))
        .ToList();

    JavaScriptSerializer jsonSerializer = new JavaScriptSerializer();
    var jsonString = jsonSerializer.Serialize(filteredEmployees).ToString();
    return Content(jsonString);
}

The list is retrieved OK, but when I serialize it, I get this exception;

System.ObjectDisposedException: The ObjectContext instance has been
 disposed and can no longer be used for
 operations that require a connection.
     Generated: Wed, 17 Nov 2010 16:06:56 GMT

 System.ObjectDisposedException: The ObjectContext instance has been
 disposed and can no longer be used for operations that require a connection. 
 at
 System.Data.Objects.ObjectContext.EnsureConnection()
 at
 System.Data.Objects.ObjectQuery`1.GetResults(Nullable`1 forMergeOption)     at
 System.Data.Objects.ObjectQuery`1.Execute(MergeOption mergeOption)     at
 System.Data.Objects.DataClasses.EntityCollection`1.Load(List`1 collection, MergeOption mergeOption)  at
 System.Data.Objects.DataClasses.EntityCollection`1.Load(MergeOption mergeOption)     at
 System.Data.Objects.DataClasses.RelatedEnd.Load() at
 System.Data.Objects.DataClasses.RelatedEnd.DeferredLoad() at
 System.Data.Objects.DataClasses.EntityCollection`1.System.Collections.IEnumerable.GetEnumerator() at
 System.Web.Script.Serialization.JavaScriptSerializer.SerializeEnumerable(IEnumerable enumerable, StringBuilder sb, Int32 depth, Hashtable objectsInUse, SerializationFormat serializationFormat)     at
 System.Web.Script.Serialization.JavaScriptSerializer.SerializeValueInternal(Object o, StringBuilder sb, Int32 depth, Hashtable objectsInUse, SerializationFormat serializationFormat)     at
 System.Web.Script.Serialization.JavaScriptSerializer.SerializeValue(Object o, StringBuilder sb, Int32 depth, Hashtable objectsInUse, SerializationFormat
 serializationFormat)     at
 System.Web.Script.Serialization.JavaScriptSerializer.SerializeCustomObject(Object o, StringBuilder sb, Int32 depth, Hashtable objectsInUse, SerializationFormat
 serializationFormat)     at
 System.Web.Script.Serialization.JavaScriptSerializer.SerializeValueInternal(Object o, StringBuilder sb, Int32 depth, Hashtable objectsInUse, SerializationFormat
 serializationFormat)     at
 System.Web.Script.Serialization.JavaScriptSerializer.SerializeValue(Object
 o, StringBuilder sb, Int32 depth, Hashtable objectsInUse, SerializationFormat
 serializationFormat)     at
 System.Web.Script.Serialization.JavaScriptSerializer.SerializeEnumerable(IEnumerable enumerable, StringBuilder sb, Int32 depth, Hashtable objectsInUse,
 SerializationFormat
 serializationFormat)     at
 System.Web.Script.Serialization.JavaScriptSerializer.SerializeValueInternal(Object o, StringBuilder sb, Int32 depth, Hashtable objectsInUse, SerializationFormat
 serializationFormat)     at
 System.Web.Script.Serialization.JavaScriptSerializer.SerializeValue(Object
 o, StringBuilder sb, Int32 depth, Hashtable objectsInUse, SerializationFormat
 serializationFormat)     at
 System.Web.Script.Serialization.JavaScriptSerializer.Serialize(Object
 obj, StringBuilder output, SerializationFormat serializationFormat)     at
 System.Web.Script.Serialization.JavaScriptSerializer.Serialize(Object
 obj, SerializationFormat serializationFormat)     at
 System.Web.Script.Serialization.JavaScriptSerializer.Serialize(Object obj)     at
 SHP.Controllers.EmployeeController.AutoCompleteResult(String searchText) in C:Documents and SettingsgeoffreypayneMy DocumentsVisual Studio
 2010ProjectsMVCSHPSHPControllersEmployeeController.cs:line
 623     at lambda_method(Closure , ControllerBase , Object[] )     at
 System.Web.Mvc.ActionMethodDispatcher.Execute(ControllerBase controller, Object[] parameters)    at
 System.Web.Mvc.ReflectedActionDescriptor.Execute(ControllerContext
 controllerContext, IDictionary`2 parameters)     at
 System.Web.Mvc.ControllerActionInvoker.InvokeActionMethod(ControllerContext
 controllerContext, ActionDescriptor actionDescriptor, IDictionary`2 parameters)     at
 System.Web.Mvc.ControllerActionInvoker.<>c__DisplayClassd.InvokeActionMethodWithFilters>b__a()
 at
 System.Web.Mvc.ControllerActionInvoker.InvokeActionMethodFilter(IActionFilter
 filter, ActionExecutingContext preContext, Func`1 continuation)    
 at
 System.Web.Mvc.ControllerActionInvoker.<>c__DisplayClassd.<>c__DisplayClassf.<InvokeActionMethodWithFilters>b__c() at
 System.Web.Mvc.ControllerActionInvoker.InvokeActionMethodWithFilters(ControllerContext controllerContext, IList`1 filters, ActionDescriptor actionDescriptor, IDictionary`2 parameters)     at
 System.Web.Mvc.ControllerActionInvoker.InvokeAction(ControllerContext
 controllerContext, String actionName)

I find this very odd. I have already retrieved the list of employees and the DataContext has been disposed. So why would I get this error?

Answer 1

It sounds like you have some lazily loaded relationship properties that have not yet loaded (which has an associated "n+1" performance concern). You can try eager loading to see if this helps; otherwise, explicitly load the data for each item in the list, before you close the object-context.