Query a winforms control with CheckedListBoxItemCollection.AsQueryable().Provider.CreateQuery(

I need to query a winforms control(CheckedListBoxControl) having a CheckedListBoxItemCollection which I want to query for a certain Id that is within the property "Value" of the CheckedListBoxItem.

CheckedListBoxItemCollection items = myCheckedListBoxControl.Items;

foreach(Department dep in departmentList)
{
  bool isDepExisting = items.AsQueryable().Where( the .Where clause does not exist );
  // How can I query for the current dep.Id in the departmentList and compare this   dep.Id with  every Item.Value in the CheckedListBoxContro开发者_开发百科l and return a bool from the result ???   
  if(!isDepExisting)
      myCheckedListBoxControl.Items.Add( new CheckedListBoxItem(dep.id);
}

UPDATE:

IEnumberable<CheckedListBoxItem> checks = items.Cast<CheckedListBoxItem>().Where(item => item.Value.Equals(dep.InternalId));

Why says Visual Studio that the IEnumerable or the IEnumberable namespace of it can not be found? When I use "var" instead then I can compile my code. But the boss in my company forbide my to use var...

CheckListBox.Items only implements IEnumerable, not IEnumerable<T>. You get the overload of AsQueryable() that returns IQueryable (not the generic one). Which only has the Cast and OfType extension methods.

Cast the items back from object to Department. Like this:

var q = checkedListBox1.Items.Cast<Department>().AsQueryable().Where((d) => d.Id == 1);

You don't need AsQueryable() anymore btw.