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dotnet xml
group:How to: Omit Deafulted Elements from XML When Serializing
dotnet xml:
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
(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. [quoted text, click to view] "Charles Law" <blank@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 > >
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 "Clive Dixon" <clived.noluncheonmeat@digita.noluncheonmeat.com> wrote in message news:eif4czaJGHA.3176@TK2MSFTNGP12.phx.gbl... [quoted text, click to view] > (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" <blank@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 >> >> > >
Charles,
I had quite forgotten about the other methods you discovered - have no idea whether they still function in the same way in 2.0. The 'propertyNameSpecified' method seems much more flexible though. If you look in the VS2003 help for XmlSerializer class ('about XMLSerializer class'), about half way down the page is the following (I suspect the MSDN documentation for this will be identical): Another option is to use a special pattern to create a Boolean field recognized by the XmlSerializer, and to apply the XmlIgnoreAttribute to the field. The pattern is created in the form of propertyNameSpecified. For example, if there is a field named "MyFirstName" you would also create a field named "MyFirstNameSpecified" that instructs the XmlSerializer whether or not to generate the XML element named "MyFirstName". This is shown in the following C# and Visual Basic example. ' Visual Basic Public Class OptionalOrder ' This field's value shouldn't be serialized ' if it is uninitialized. Public FirstOrder As String ' Use the XmlIgnoreAttribute to ignore the ' special field named "FirstOrderSpecified". <System.Xml.Serialization.XmlIgnoreAttribute> _ Public FirstOrderSpecified As Boolean End Class [quoted text, click to view] "Charles Law" <blank@nowhere.com> wrote in message news:OT$P2UbJGHA.668@TK2MSFTNGP11.phx.gbl... > 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 >
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