How to: Omit Deafulted Elements from XML When Serializing

28 Jan 2006 6:36 PM

Charles Law

I have a complex object that I am serializing, and I would like to omit
elements that have a default value.

For example, if I have a class as follows

Public Class Test

    Private m_Name As String = "George"
    Private m_Active As Boolean = False
    Private m_Address As String

    Public Property Name() As String
        Get
            Return m_Name
        End Get
        Set(ByVal Value As String)
            m_Name = Value
        End Set
    End Property

    Public Property Active() As Boolean
        Get
            Return m_Active
        End Get
        Set(ByVal Value As Boolean)
            m_Active = Value
        End Set
    End Property

    Public Property Address() As String
        Get
            Return m_Address
        End Get
        Set(ByVal Value As String)
            m_Address = Value
        End Set
    End Property

End Class

If Name is "George" when I serialize the object then I don't want this
element to be included in the output. Similarly, if Active is "False" when
the object is serialized, then I don't want that element included in the
output either. Anything different, and they should be included.

Is there a way to do this, perhaps by tagging the property/element in some
way? I am using VS2003.

TIA

Charles

30 Jan 2006 2:52 PM

Clive Dixon

(Apologies for any bad VB in advance - I'm a C# person)
For each field add a corresponding Boolean field & property suffixed with
Specified (and the property has attribute XmlIgnore), such as:

Public Class Test

    Private m_Name As String = "George"
    Private m_NameSpecified As Boolean = False

    Public Property Name() As String
        Get
            Return m_Name
        End Get
        Set(ByVal Value As String)
            m_Name = Value
            m_NameSpecified = True
        End Set
    End Property

    <XmlIgnore()>
    Public Property NameSpecified() As Boolean
        Get
            Return m_NameSpecified
        End Get
        Set(ByVal Value As Boolean)
            m_NameSpecified = Value
        End Set
    End Property

The framework on serializing each field looks for a field of type Boolean
with the field name suffixed with "Specified". If this field exists and has
value False, the field will not be serialized.

Note that in the original field's Set accessor I set the XXXSpecified field
to True. This means that if I ever set the property then it will get
serialized; if I don't set it, it won't. If you specifically want it so that
if it's not "George" it will be serialized then that is easy enough for you
to change appropriately.

Show quoteHide quote

"Charles Law" <bl***@nowhere.com> wrote in message
news:%232KE3mDJGHA.2668@tk2msftngp13.phx.gbl...
>I have a complex object that I am serializing, and I would like to omit
>elements that have a default value.
>
> For example, if I have a class as follows
>
> Public Class Test
>
>    Private m_Name As String = "George"
>    Private m_Active As Boolean = False
>    Private m_Address As String
>
>    Public Property Name() As String
>        Get
>            Return m_Name
>        End Get
>        Set(ByVal Value As String)
>            m_Name = Value
>        End Set
>    End Property
>
>    Public Property Active() As Boolean
>        Get
>            Return m_Active
>        End Get
>        Set(ByVal Value As Boolean)
>            m_Active = Value
>        End Set
>    End Property
>
>    Public Property Address() As String
>        Get
>            Return m_Address
>        End Get
>        Set(ByVal Value As String)
>            m_Address = Value
>        End Set
>    End Property
>
> End Class
>
> If Name is "George" when I serialize the object then I don't want this
> element to be included in the output. Similarly, if Active is "False" when
> the object is serialized, then I don't want that element included in the
> output either. Anything different, and they should be included.
>
> Is there a way to do this, perhaps by tagging the property/element in some
> way? I am using VS2003.
>
> TIA
>
> Charles
>
>

30 Jan 2006 3:52 PM

Charles Law

Hi Clive

That does exactly what I want. Thanks.

I have never seen this documented, can you point me to an MSDN description
of this feature?

Whilst looking myself, I came across another way that seems to work:

<ComponentModel.DefaultValue("George")> _
Public Property Name() As String
    Get
        Return m_Name
    End Get
    Set(ByVal Value As String)
        m_Name = Value
    End Set
End Property

Name now does not get serialized when it returns "George". Also,
XmlAttributes.XmlDefaultValue can be used to do the same thing at runtime.
The only concern with this is that MSDN article KB325691 highlights that
Microsoft intend to change this behaviour in the next major version release
of the .NET framework. I haven't checked, but I wonder if this technique no
longer works in .NET 2.0.

Anyway, many thanks again.

Charles

Show quoteHide quote

"Clive Dixon" <clived.noluncheonm***@digita.noluncheonmeat.com> wrote in
message news:eif4czaJGHA.3176@TK2MSFTNGP12.phx.gbl...
> (Apologies for any bad VB in advance - I'm a C# person)
> For each field add a corresponding Boolean field & property suffixed with
> Specified (and the property has attribute XmlIgnore), such as:
>
> Public Class Test
>
>    Private m_Name As String = "George"
>    Private m_NameSpecified As Boolean = False
>
>    Public Property Name() As String
>        Get
>            Return m_Name
>        End Get
>        Set(ByVal Value As String)
>            m_Name = Value
>            m_NameSpecified = True
>        End Set
>    End Property
>
>    <XmlIgnore()>
>    Public Property NameSpecified() As Boolean
>        Get
>            Return m_NameSpecified
>        End Get
>        Set(ByVal Value As Boolean)
>            m_NameSpecified = Value
>        End Set
>    End Property
>
> The framework on serializing each field looks for a field of type Boolean
> with the field name suffixed with "Specified". If this field exists and
> has value False, the field will not be serialized.
>
> Note that in the original field's Set accessor I set the XXXSpecified
> field to True. This means that if I ever set the property then it will get
> serialized; if I don't set it, it won't. If you specifically want it so
> that if it's not "George" it will be serialized then that is easy enough
> for you to change appropriately.
>
> "Charles Law" <bl***@nowhere.com> wrote in message
> news:%232KE3mDJGHA.2668@tk2msftngp13.phx.gbl...
>>I have a complex object that I am serializing, and I would like to omit
>>elements that have a default value.
>>
>> For example, if I have a class as follows
>>
>> Public Class Test
>>
>>    Private m_Name As String = "George"
>>    Private m_Active As Boolean = False
>>    Private m_Address As String
>>
>>    Public Property Name() As String
>>        Get
>>            Return m_Name
>>        End Get
>>        Set(ByVal Value As String)
>>            m_Name = Value
>>        End Set
>>    End Property
>>
>>    Public Property Active() As Boolean
>>        Get
>>            Return m_Active
>>        End Get
>>        Set(ByVal Value As Boolean)
>>            m_Active = Value
>>        End Set
>>    End Property
>>
>>    Public Property Address() As String
>>        Get
>>            Return m_Address
>>        End Get
>>        Set(ByVal Value As String)
>>            m_Address = Value
>>        End Set
>>    End Property
>>
>> End Class
>>
>> If Name is "George" when I serialize the object then I don't want this
>> element to be included in the output. Similarly, if Active is "False"
>> when the object is serialized, then I don't want that element included in
>> the output either. Anything different, and they should be included.
>>
>> Is there a way to do this, perhaps by tagging the property/element in
>> some way? I am using VS2003.
>>
>> TIA
>>
>> Charles
>>
>>
>
>