Xml serialization - Hide null values

Question

When using a standard .NET Xml Serializer, is there any way I can hide all null values? The below is an example of the output of my class. I don't want to output the nullable integers if they are set to null.

Current Xml output:

<?xml version="1.0" encoding="utf-8"?>
<myClass>
   <myNullableInt p2:nil="true" xmlns:p2="http://www.w3.org/2001/XMLSchema-instance" />
   <myOtherInt>-1</myOtherInt>
</myClass>

What I want:

<?xml version="1.0" encoding="utf-8"?>
<myClass>
   <myOtherInt>-1</myOtherInt>
</myClass>

Chris Taylor · Accepted Answer · 2011-04-28 12:48:32Z

299

You can create a function with the pattern ShouldSerialize{PropertyName} which tells the XmlSerializer if it should serialize the member or not.

For example, if your class property is called MyNullableInt you could have

public bool ShouldSerializeMyNullableInt() 
{
  return MyNullableInt.HasValue;
}

Here is a full sample

public class Person
{
  public string Name {get;set;}
  public int? Age {get;set;}
  public bool ShouldSerializeAge()
  {
    return Age.HasValue;
  }
}

Serialized with the following code

Person thePerson = new Person(){Name="Chris"};
XmlSerializer xs = new XmlSerializer(typeof(Person));
StringWriter sw = new StringWriter();
xs.Serialize(sw, thePerson);

Results in the followng XML - Notice there is no Age

<Person xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
        xmlns:xsd="http://www.w3.org/2001/XMLSchema">
  <Name>Chris</Name>
</Person>

edited Apr 28, 2011 at 12:48

answered Apr 28, 2011 at 12:28

Chris Taylor

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18 Comments

schei1 Over a year ago

One word: Awesome! MSDN ShouldSerialize

Matze Over a year ago

The ShouldSerialize pattern does only work, if the property is not marked with an XmlAttribute-attribute (I thought this should work, because an attribute could be optional, but it does not).

Chris Taylor Over a year ago

@Matze interesting, I have not tried that. I would also have assumed it would work.

Matze Over a year ago

@ChrisTaylor Yes; I assumed the same. The tricky thing was that the creation of the XmlSerializer instance failed (due to an error when reflecting the type) until I removed the XmlAttribute from the nullable int-property.

RooiWillie Over a year ago

@PierredeLESPINAY - From visual studio 2015 and up, you could use: public bool ShouldSerializeAge() => Age.HasValue;

|

Daniel Rose · Accepted Answer · 2012-12-10 11:54:41Z

43

Additionally to what Chris Taylor wrote: if you have something serialized as an attribute, you can have a property on your class named {PropertyName}Specified to control if it should be serialized. In code:

public class MyClass
{
    [XmlAttribute]
    public int MyValue;

    [XmlIgnore]
    public bool MyValueSpecified;
}

edited Dec 10, 2012 at 11:54

answered Apr 28, 2011 at 12:48

Daniel Rose

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3 Comments

sinsedrix Over a year ago

Be carefull, {PropertyName}Specified attributes have to be of type bool.

OfirD Over a year ago

Works also as a function. For example, if MyValue is int?, one could do public bool MyValueSpecified => MyValue.HasValue;.

Gh61 Over a year ago

@OfirD public bool MyValueSpecified => MyValue.HasValue; is not function. It is getter only property. Same as: public bool MyValueSpecified { get { return MyValue.HasValue; } }

JPBlanc · Accepted Answer · 2011-04-28 13:29:18Z

33

It exists a property called XmlElementAttribute.IsNullable

If the IsNullable property is set to true, the xsi:nil attribute is generated for class members that have been set to a null reference.

The following example shows a field with the XmlElementAttribute applied to it, and the IsNullable property set to false.

public class MyClass
{
   [XmlElement(IsNullable = false)]
   public string Group;
}

You can have a look to other XmlElementAttribute for changing names in serialization etc.

edited Apr 28, 2011 at 13:29

answered Apr 28, 2011 at 12:43

JPBlanc

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2 Comments

Vincent Sels Over a year ago

Unfortunately, this only works for reference types, not for value types or their Nullable counterparts.

bouvierr Over a year ago

@VincentSels is correct. MSDN says: You cannot apply the IsNullable property to a member typed as a value type because a value type cannot contain null. Additionally, you cannot set this property to false for nullable value types. When such types are null, they will be serialized by setting xsi:nil to true.

MichaelSo · Accepted Answer · 2013-12-15 19:09:42Z

15

You can define some default values and it prevents the fields from being serialized.

    [XmlElement, DefaultValue("")]
    string data;

    [XmlArray, DefaultValue(null)]
    List<string> data;

answered Dec 15, 2013 at 19:09

MichaelSo

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1 Comment

bubi Over a year ago

Unfortunately, this does not work for nullable value types

Durga Nunna · Accepted Answer · 2016-06-10 20:46:20Z

I prefer creating my own xml with no auto-generated tags. In this I can ignore creating the nodes with null values:

public static string ConvertToXML<T>(T objectToConvert)
    {
        XmlDocument doc = new XmlDocument();
        XmlNode root = doc.CreateNode(XmlNodeType.Element, objectToConvert.GetType().Name, string.Empty);
        doc.AppendChild(root);
        XmlNode childNode;

        PropertyDescriptorCollection properties = TypeDescriptor.GetProperties(typeof(T));
        foreach (PropertyDescriptor prop in properties)
        {
            if (prop.GetValue(objectToConvert) != null)
            {
                childNode = doc.CreateNode(XmlNodeType.Element, prop.Name, string.Empty);
                childNode.InnerText = prop.GetValue(objectToConvert).ToString();
                root.AppendChild(childNode);
            }
        }            

        return doc.OuterXml;
    }

Sagar · Accepted Answer · 2014-05-07 13:59:20Z

1

In my case the nullable variables/elements were all String type. So, I simply performed a check and assigned them string.Empty in case of NULL. This way I got rid of the unnecessary nil and xmlns attributes (p3:nil="true" xmlns:p3="http://www.w3.org/2001/XMLSchema-instance)

// Example:

myNullableStringElement = varCarryingValue ?? string.Empty

// OR

myNullableStringElement = myNullableStringElement ?? string.Empty

answered May 7, 2014 at 13:59

Sagar

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1 Comment

ZafarYousafi Over a year ago

This solutions very limited and only works with string. For other types empty string is still a value. Some parsers try to find attribute and if found try to convert the value to target type. For such parsers, missing attribute means null and if there is attribute then it must have a valid value.

Rauld · Accepted Answer · 2012-10-18 10:40:51Z

0

private static string ToXml(Person obj)
{
  XmlSerializerNamespaces namespaces = new XmlSerializerNamespaces();
  namespaces.Add(string.Empty, string.Empty);

  string retval = null;
  if (obj != null)
  {
    StringBuilder sb = new StringBuilder();
    using (XmlWriter writer = XmlWriter.Create(sb, new XmlWriterSettings() { OmitXmlDeclaration = true }))
    {
      new XmlSerializer(obj.GetType()).Serialize(writer, obj,namespaces);
    }
    retval = sb.ToString();
  }
  return retval;
}

answered Oct 18, 2012 at 10:40

Rauld

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1 Comment

Louis Somers Over a year ago

That only removes the specifications on the Root, but then you get extra specifications fer each and every NULL value on nullable reference types...

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