Error : Collection was modified; enumeration operation may not execute.

Question

Hello !

I'm using EF6 , VB.net 2013.

I'm trying to implement a way to copy an object to a new object.

This is my code :

<Extension> _
    Public Sub CopyTo(Of T)(copyFrom As T, copyTo__1 As T, copyParentProperties As Boolean)
        Dim props As PropertyInfo()
        If copyParentProperties Then
            props = GetType(T).GetProperties()
        Else
            props = GetType(T).GetProperties(BindingFlags.[Public] Or BindingFlags.Instance Or BindingFlags.DeclaredOnly)
        End If
        Dim i As Integer = 0
        While i < props.Length
            Dim propertyValue = copyFrom.[GetType]().GetProperty(props(i).Name).GetValue(copyFrom, Nothing)
            copyTo__1.[GetType]().GetProperty(props(i).Name).SetValue(copyTo__1, propertyValue, Nothing)
            System.Math.Max(System.Threading.Interlocked.Increment(i), i - 1)
        End While
    End Sub

But when I try to use the code like this :

newitm = New Myobject
currentobj.CopyTo(newitm, False)
context.MyObjects.Add(Newitm)
context.savechanges

I get this error , on the line----- context.MyObjects.Add(Newitm) -------

An unhandled exception of type 'System.InvalidOperationException' occurred in System.Core.dll
 
Additional information: Collection was modified; enumeration operation may not execute.

(But of course , if i create a new object and fill the properties manually one by one , the ADD method works without problems. )

What may be the problem ?
Thank you !

Answer 1

Hello,

>>What may be the problem ?

There are some unclear points are:

Where do you add your extension method?

What is the currentobj object and how do you declare it and assign valves to it?

It is also confused your call the “currentobj.CopyTo(newitm, False)” while you provided an extension method which accepts three parameters().

Based on your provided code, I created a demo and it could work with the extension method:

Sub Main()

        Dim context As WinFormDBEntities = New WinFormDBEntities

        Dim order As Order = New Order() With {.ID = 1, .Name = "1"}

        Dim copiedOrder As Order = New Order

        order.CopyTo(order, copiedOrder, False)

        context.Orders.Add(copiedOrder)

        context.SaveChanges()

    End Sub

You could check it to see if this would also work on your side.

Regards.

---

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Answer 2

Hello !

Your code works , because you create a new object  , and immediately copy this.

My CurrentObj is an existing object that I have read like this :

MyBindingSource.Datasource=(For t in context.MyObjects select t).Tolist

.....

CurrentObj = MyBindingsource.current

.......

and as for the extension , is declared on a module , and I call with only 2 parameters ( the new object and the Boolean parameter ). But I have no problem on this call. the problem is when I try to add the newitm . 

Answer 3

Hello,

It seems to be BindingSource object in window form, with your code, I also created a test as:

Imports System.Reflection

Imports System.Runtime.CompilerServices

Imports System.Windows.Forms


Module Module1



    Sub Main()

        Dim MyBindingSource As BindingSource = New BindingSource


        Dim context As WinFormDBEntities = New WinFormDBEntities

        MyBindingSource.DataSource = (From o In context.Orders).ToList



        Dim order As Order = New Order()

        Dim copiedOrder As Order = MyBindingSource.Current

        order.CopyTo(copiedOrder, order, False)

        context.Orders.Add(copiedOrder)

        context.SaveChanges()

    End Sub-


End Module

It however still works, I do not know what exactly operation you have done for the bindingsource object, if possible, please share more code with us.

Regards.

---

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