Entity Framework : Why this extension is not usable ?

dilkonika

Hello ! I'm using entity framework 6 with Vb.net 2013. I'm trying to add an extension. This is the code :

Imports System.ComponentModel
Imports System.Collections
Imports System.Data.Entity.Core.Objects.DataClasses
Imports System.Runtime.Serialization
Imports System.IO
Imports System.Reflection

Module Extensions
_
Public Function Clone(Of T As EntityObject)(source As T) As T
Dim ser = New DataContractSerializer(GetType(T))
Using stream = New MemoryStream()
ser.WriteObject(stream, source)
stream.Seek(0, SeekOrigin.Begin)
Return CType(ser.ReadObject(stream), T)
End Using
End Function
End Module

But if I try to use like this :

Dim litm, newitm as MyObject
For Each litm In itemlist
newitm = litm.Clone()
...
Next

I'm getting this error :

'Clone' is not a member of 'TheProg.MyObject'

What's the problem ?

Dave Kreskowiak

Your ``MyObject`` class doesn't have a ``Clone()`` method. It's not supplied to your class automatically, after all how would a default implementation know how to correctly copy your class? It wouldn't. YOU have to implement a ``Clone()`` method yourself.

A guide to posting questions on CodeProject

Click this: Asking questions is a skill. Seriously, do it.
Dave Kreskowiak

dilkonika

sorry , but why the method Clone is not added as extension ? Have I done something wrong constructing the extension ?

Dave Kreskowiak

Wow an I tired. It's 2:00am here. I didn't even notice the Clone method name... What does your ``MyObject`` class look like? Are you using Database First, Code First, or what?

A guide to posting questions on CodeProject

Click this: Asking questions is a skill. Seriously, do it.
Dave Kreskowiak

dilkonika

I'm using Database First.

Partial Public Class Myobject
Public Property id As Integer
Public property name as string
Public Overridable Property chld As ICollection(Of chld) = New HashSet(Of chld)
End Class

Partial Public Class chld
Public Property id As Integer
Public Property date1 as DateTime
Public Property quantity as Integer
Public Property ParentID as integer
Public Overridable Property MyObj1 As MyObject
End Class

Dave Kreskowiak

It doesn't work because Database First entity objects inherit from ``Object``, not ``EntityObject``. Your current Close method would work just fine for a Code First EF model. The only way to get the ``Clone()`` to work is to remove the "As EntityObject" restriction in the function header. Of course, this is going to make your ``Clone()`` method available for every type in the application.

A guide to posting questions on CodeProject

Click this: Asking questions is a skill. Seriously, do it.
Dave Kreskowiak

dilkonika

I remove the "As entityobject". Now , on runtime , I get this error on the line : ser.WriteObject(stream, source) :

An unhandled exception of type 'System.Runtime.Serialization.SerializationException' occurred in System.Runtime.Serialization.dll

Additional information: Type 'System.Data.Entity.DynamicProxies.MyObject_F2FFE64DA472EB2B2BDF7E143DE887D3845AD9D1731FD3107937062AC0C2E4BB' with data contract name 'MyObject_F2FFE64DA472EB2B2BDF7E143DE887D3845AD9D1731FD3107937062AC0C2E4BB:http://schemas.datacontract.org/2004/07/System.Data.Entity.DynamicProxies' is not expected. Consider using a DataContractResolver or add any types not known statically to the list of known types - for example, by using the KnownTypeAttribute attribute or by adding them to the list of known types passed to DataContractSerializer.

Dave Kreskowiak

I don't know what you've got wrong because I can't replicated it. This is the modified extension code I used:

Imports System.Data.Entity.Core.Objects.DataClasses
Imports System.Runtime.Serialization
Imports System.IO
Imports System.Runtime.CompilerServices
Imports System.Data.Objects

Module Extensions

Public Function Clone(Of T)(source As T) As T
    Dim ser = New DataContractSerializer(GetType(T))
    Using stream = New MemoryStream()
        ser.WriteObject(stream, source)
        stream.Seek(0, SeekOrigin.Begin)
        Return CType(ser.ReadObject(stream), T)
    End Using
End Function

End Module

A guide to posting questions on CodeProject

Click this: Asking questions is a skill. Seriously, do it.
Dave Kreskowiak

dilkonika

This exactly the same code that I have used. but I get the error that I have posted before.

Dave Kreskowiak

It just dawned on me why you're getting that error. The object you're trying to Clone is referencing other object in the database that haven't been re-hydrated by EF yet. That's where those strange looking proxy objects are coming from. In order to get it to work, you have to load the objects being referenced before you try and Close the base object.

A guide to posting questions on CodeProject

Click this: Asking questions is a skill. Seriously, do it.
Dave Kreskowiak

dilkonika

The way I'm getting the object that i want to clone is this : -I have a listbox bound to a bindingsource (that have as datasource = (From t in context.Myobjects where t.id>5 select t ).Tolist - The user select several items from listbox. - I have a listitm=New list(of Myobject) , where i add one by one the items selected from listbox. - After i have the code that i posted to my question :

Dim litm, newitm as MyObject
For Each litm In itemlist
newitm = litm.Clone()
...
Next

so in this situation , do you have an idea why i have those strange looking proxy objects like : MyObject_F2FFE64DA472EB2B2BDF7E143DE887D3845AD9D1731FD3107937062AC0C2E4BB Thank you !

Dave Kreskowiak

I just told you why. The object has a reference to another related object that EF hasn't loaded.

A guide to posting questions on CodeProject

Click this: Asking questions is a skill. Seriously, do it.
Dave Kreskowiak

dilkonika

Actually , i have loaded all referenced object , but i think some of them are loaded only with some of the properties. MyObjects - ob1 I have loaded ob1 like below : Myob1list=(From t in context.ob1s Select t.id,t.name).Tolist May be this the problem , and if yes , what should i do ? Thank you !

Dave Kreskowiak

You have to load the child objects in your query:

Myob1list = (From t in context.ob1s.Include("chld")
             Select t).ToList()

(I'm converting C# code from memory. I haven't touched VB.NET in a few years now.)

A guide to posting questions on CodeProject

Click this: Asking questions is a skill. Seriously, do it.
Dave Kreskowiak

dilkonika

Sorry , but I'm using lazyloading. and I've read that these proxy objects , are related with using of lazyloading. So , why all other actions that I do with my objects works without problems, and this Clone action produce errors ?

Dave Kreskowiak

dilkonika wrote:

Sorry , but I'm using lazyloading. and I've read that these proxy objects , are related with using of lazyloading.

Yeah, I can see that.

dilkonika wrote:

So , why all other actions that I do with my objects works without problems, and this Clone action produce errors ?

Because the proxy classes are dynamically generated by EF and are not serializable.

A guide to posting questions on CodeProject

Click this: Asking questions is a skill. Seriously, do it.
Dave Kreskowiak

Sascha Lefevre

dilkonika wrote:

Sorry , but I'm using lazyloading.

That doesn't mean you can't tell EF it should eager-load dependencies when you need it (which is what Include(..) does).

dilkonika

yes , but when I call the extension , these objects are already loaded in the way that I have described.