error:The ObjectContext instance has been disposed and can no longer be used for operations that require a connection
c#, entity-framework, wpf
Solution
`Company` should be lazy-loaded in your case. But your entity now in detached state (context which loaded `KBrand` entity now disposed. So, when you are trying to access `Company` property, Entity Framework tries to use disposed context to make query to server. That gives you exception.
You need to attach your `KBrand` entity to current context in order to enable lazy-loading
RSPDbContext c = new RSPDbContext();
KBrand co = item.Tag as KBrand;
c.KBrands.Attach(co);
// use co.Company
OR you need to use eager loading, to have `Company` already loaded. Something like this when you getting items:
RSPDbContext db = new RSPDbContext();
var brands = db.KBrands.Include(b => b.Company).ToList();
// assign brands to listbox
Problem
i have a listbox and when i select an item from this listbox called as ListofKBrands1, i take this error message: The ObjectContext instance has been disposed and can no longer be used for operations that require a connection. In code-behind,place of this error: ``` if (co.Company != null) ``` my code: ``` private void ListofKBrands1_SelectionChanged(object sender, SelectionChangedEventArgs e) { RSPDbContext c = new RSPDbContext(); if (ListofKBrands1.SelectedItem != null) { ListBoxItem item = ListofKBrands1.SelectedItem as ListBoxItem; KBrand co = item.Tag as KBrand; if (ListofKBrands1.SelectedItem != null) txtNewKBrand.Text = co.Name; else txtNewKBrand.Text = ""; int count = 0; if (co.Company != null) { foreach (string a in cbCompany.Items) { if (a == co.Company.Name) cbCompany.SelectedIndex = count; count++; } } else cbCompany.SelectedIndex = 0; } } ``` before error: my KBrand.cs: ``` public class KBrand { [Key] public int Id { get; set; } public String Name { get; set; } public virtual Company Company { get; set; } public override string ToString() { return Name; } } ``` company.cs: ``` public class Company { [Key] public int Id { get; set; } public String Name { get; set; } public override string ToString() { return Name; } } ``` if company of selected KBrand is null, this error does not appear. but if company of selected KBrand is not null, i take this error.how can i fix this error ? thanks in advance.