Auto Generated POCO serialization with DataContractSerializer and MetaDataTypeAttribute problem

Question

As the title says, i am having some problems with serializing my auto generated POCO objects. But first some background information:

I have created my Data Access Layer using EF 4.0 en ADO.Net POCO Entity Generator following this guide: http://blogs.msdn.com/b/adonet/archive/2010/01/25/walkthrough-poco-template-for-the-entity-framework.aspx .

I have now 2 class libraries, one with EF model and second with T4 Auto generated POCO entities.

Currently i am working on another project where i want to use my DAL class libraries. I must retrieve some objects and serialize them to XML. First i tried XmlSerializer, but then i found out that it has problems with circural references. I fixed this problem using XmlIgnore, but then i had problem with serializing:

Public Overridable Property NwlGroup As ICollection(Of NwlGroup) 

Because XmlSerializer does not support interfaces.

Second i tried DataContractSerializer with [DataContract] and [DataMember] attributes in autogenerated entity Poco Class file. This worked, but naturally i had to clean up the changes from the auto generated file, therefor i wanted to use MetaDataType attribute. I created extra file like this:

Imports System.Runtime.Serialization
Imports System.ComponentModel.DataAnnotations

<MetadataType(GetType(NewsletterCustomerMetadata))>
Partial Public Class NewsletterCustomer
End Class

<DataContract()
Public Class NewsletterCustomerMetadata

    <DataMember(Name:="emailaddress", IsRequired:=True)>
    Public Overridable Property Emailaddress As String

    <DataMember(Name:="name")>
    Public Overridable Property Name As String

    <DataMember()>
    Public Overridable Property NwlGroup As ICollection(Of NwlGroup)
End Class

Auto generated file:

'------------------------------------------------------------------------------
' <auto-generated>
'     This code was generated from a template.
'
'     Changes to this file may cause incorrect behavior and will be lost if
'     the code is regenerated.
' </auto-generated>
'------------------------------------------------------------------------------
Imports System
Imports System.Collections
Imports System.Collections.Generic
Imports System.Collections.ObjectModel
Imports System.Collections.Specialized
Imports System.Runtime.Serialization



Public Class NewsletterCustomer
#Region "Primitive Properties"

    Public Overridable Property ID As Integer

    Public Overridable Property Emailaddress As String

    Public Overridable Property Name As String

...

#Region "Navigation Properties"
    Public Overridable Property NwlGroup As ICollection(Of NwlGroup)
        Get
            If _nwlGroup Is Nothing Then
                Dim newCollection As New FixupCollection(Of NwlGroup)
                AddHandler newCollection.CollectionChanged, AddressOf FixupNwlGroup
                _nwlGroup = newCollection
            End If
            Return _nwlGroup
        End Get
        Set(ByVal value As ICollection(Of NwlGroup))
            If _nwlGroup IsNot value Then
                Dim previousValue As FixupCollection(Of NwlGroup) = TryCast(_nwlGroup, FixupCollection(Of NwlGroup))
                If previousValue IsNot Nothing Then
                    RemoveHandler previousValue.CollectionChanged, AddressOf FixupNwlGroup
                End If
                _nwlGroup = value
                Dim newValue As FixupCollection(Of NwlGroup) = TryCast(value, FixupCollection(Of NwlGroup))
                If newValue IsNot Nothing Then
                    AddHandler newValue.CollectionChanged, AddressOf FixupNwlGroup
                End If
            End If
        End Set
    End Property
    Private _nwlGroup As ICollection(Of NwlGroup)

...
End Class

Then i try to serialize it to xml

    Dim ctx = New ModelEntities(_connectionString)
       ctx.ContextOptions.ProxyCreationEnabled = False
       ctx.ContextOptions.LazyLoadingEnabled = False

    Dim customers = From c In ctx.NwlCustomer
                    Select c
                   Where c.SiID = 99

    Dim filename As String = "C:\test.txt"
    Dim result As NewsletterCustomer = customers.ToList.FirstOrDefault
    Dim writer As New FileStream(filename, FileMode.Create)
    Dim ser As New DataContractSerializer(GetType(NewsletterCustomer))
    ser.WriteObject(writer, customers.ToList.FirstOrDefault)
    writer.Close()

This gave me NewsletterCustomer xml with all read / write properties serialized as you would excpect when no DataContract is specified. If i move DataContract attribute from NewsletterCustomerMetadata to NewsletterCustomer then i only get the root node as you would expect when DataContract is specified with no DataMember attributes.

It looks like DataContractSerializer don't work with MetaDataType Data Annotations.

My Questions are:

1. How can i serialize my POCO Classes to CUSTOM XML?
2. How can i add [DataContract] and [DataMember] attributes to auto generated POCO classes?
3. What is the best way to serialize Auto Generated POCO classes to XML?

Answer 1

DataContractSerializer doesn't read attributes from external metadata type. Not every feature of .NET framework works with rest of the API especially newer features usually don't work with old ones and that is exactly this case.

The best way is either use custom serialization in IXmlSerializable or DTO as @Marc suggested. In case of DataContractSerializer you can also use IDataContractSurrogate. Very advanced scenario of XmlSerializer is overriding XML serialization.

It is also possible to let T4 template generate attributes for you but that is very advanced technique because it requires two steps:

• Manually modify EDMX file (as XML) and add structural annotations into CSDL part (part defining your entities). Structural annotations are custom XML elements. Example of using structural annotation in reverse process (controlling SQL generation).
• Modify T4 template to load your custom structural annotations and use them in class generation.