MVC 4-具有相同键的对象已存在于ObjectStateManager中

Question

First of all - apologies. I know that there are a lot of questions about this but I've been searching for a few days and couldn't find any solutions that I was able to tweak to my situation (or was too dull to tweak).

Essentially, this is what I'm trying to accomplish: The code shown is for saving an edit to one item in a particular class --- that functionality works fine. Then, based off the Order property of that entry, I then want to change other items' Order property in the database. Those changes are made in the For Each statement.

The error shown in the code is being thrown on EntityState.Modified. I know that the error is probably resulting from the For Each statement due to the db items basically being called upon twice; however, I'm unsure of how to fix it. Please help. Thank you!

Function Edit(<Bind(Include:="ID,Column,Order,Type,Header,Expandable,Expansion,Instruction")> ByVal checklistitem As ChecklistItem) As ActionResult

For Each x In db.Items
    If checklistitem.Order <= x.Order And checklistitem.Type = x.Type And checklistitem.ID <> x.ID Then
        x.Order += 1
    End If
Next

If ModelState.IsValid Then
    db.Entry(checklistitem).State = EntityState.Modified 'ERROR RETURNED ON THIS LINE: An object with the same key already exists in the ObjectStateManager. The existing object is in the Modified state. An object can only be added to the ObjectStateManager again if it is in the added state.'
    db.SaveChanges()
    Return RedirectToAction("Index")
End If
Return View(checklistitem)

Answer 1

your db is not instance per request?
when you show you edit form,it must read checklistitem from db ,so it will attach to db context.
and when post,a new same key obj create by mvc,so it make this err.
2 obj with same key,what attach to 1 context