How to ignore a nullable property from serialization if it is null or empty?

Question

I have a class which is used for Xml Serialization.

Inside which I have a nullable property which is decorated with XmlAttribute:

 [XmlAttribute("lastUpdated")]
 public DateTime? LastUpdated { get; set; }

How to ignore the property from serialization if it is null or empty?

I've tried the below but it doesn't serialize when there is a value (always ignores):

  [XmlIgnore]
        public DateTime? LastUpdatedValue { get; set; }

        [XmlAttribute("lastUpdated")]
       public DateTime LastUpdated { get; set; }

        public bool ShouldSerializeLastUpdated()
        {
            return LastUpdatedValue.HasValue;
        }

Have you seen this http://stackoverflow.com/questions/244953/serialize-a-nullable-int?rq=1 — Yahya, Apr 23 '13 at 14:56
What do you expect the XML to look like? In this case you'll get `` if the property is null; you could either post-process your xml (easier) or you can write a XmlWriter class (harder, performs better). There are other options that are both hard and bloat your code. — Sten Petrov, Apr 23 '13 at 14:57
no I just want to ignore the xmlattribute if it's null. but DateTime? is not serializable. How to replace it? — The Light, Apr 23 '13 at 15:09

binard · Answer 1 · 2013-04-24T08:22:17.530

11

Nullable is not directly supported by XmlSerialization.

If you want use a nullable property you must use a non nullable property and add a boolean property with the same name of property with the suffix "Specified" which specifie when the property must be serializable.

An example with your case :

    private DateTime? _lastUpdated;

    [XmlAttribute("lastUpdated")]
    public DateTime LastUpdated {
        get {
            return (DateTime)_lastUpdated;
        }
        set
        {
            _lastUpdated = value;
        }
    }

    public bool LastUpdatedSpecified
    {
        get
        {
            return _lastUpdated.HasValue;
        }
    }

edited Apr 24 '13 at 08:22

answered Apr 23 '13 at 15:40

binard

1,726
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Thanks but the problem is I can't serialize it anymore using XmlSerializer. I'm getting this error: + InnerException {"There was an error reflecting property 'LastUpdated'."} System.Exception {System.InvalidOperationException} – The Light Apr 24 '13 at 07:29
Sorry, I was too fast, I correct and edit my code. Can you try this ? – binard Apr 24 '13 at 08:22
@TheLight can you accept my answer like best response ? – binard Apr 28 '14 at 07:56
`return (DateTime)_lastUpdated;` will throw `InvalidOperationException` if `_lastUpdated` doesn't has a value. – isalgueiro Jan 29 '15 at 11:45
Where is LastUpdatedSpecified used ? – rajibdotnet Oct 22 '21 at 05:39

score 5 · Answer 2 · answered Jun 03 '16 at 17:58

I know this topic is old. This is the solution I came with. A class which encapsulates the type, and has implicit casting to the type. When serializing, the member variable can be marked with IsNullable = false without getting compiler errors, and blocking it from being serialized when null.

public class Optional<T> where T : struct, IComparable
{
    public Optional(T valueObject)
    {
        Value = valueObject;
    }

    public Optional()
    {
    }

    [XmlText]
    public T Value { get; set; }

    public static implicit operator T(Optional<T> objectToCast)
    {
        return objectToCast.Value;
    }

    public static implicit operator Optional<T>(T objectToCast)
    {
        return new Optional<T>(objectToCast);
    }
}

Then use it in your class

[Serializable]
[XmlRoot(ElementName = "foo")]
public class foo
{
   [XmlElement(ElementName = "myInteger", isNullable = false)]
   Optional<int> myInt;
}

You can do things like

        myFoo.myInt = 7;
        int j = 8 + myFoo.myInt;

For all purposes it's an int. For serialization purposes, it can be null and blocked from being serialized.

Thank you, this worked fine for me! When using it with another custom datatype (my bools need to be serialized as Y/N), I've changed the IComparable to IComparable, where I could implement IComparable in my CustomBool type — BerDev, Dec 05 '18 at 11:01
This doesn't work for [XmlElement(DataType="date")]. 'date' is an invalid value for the XmlElementAttribute.DataType property. The property may only be specified for primitive types. — JJS, Jan 30 '21 at 22:33

score 4 · Answer 3 · answered Jul 29 '16 at 06:15

This is working for me.

    [XmlIgnore]
    public float? Speed { get; set; }

    [XmlAttribute("Speed")]
    public float SpeedSerializable
    {
        get
        {
            return this.Speed.Value;
        }
        set { this.Speed = value; }
    }

    public bool ShouldSerializeSpeedSerializable()
    {
          return Speed.HasValue;
    }

score 2 · Answer 4 · answered Oct 25 '17 at 08:41

Note: This works for sure in SOAP contracts in WCF. I haven't tested in other Xml serialization scenarios.

When using a [DataContract] you can use

[DataMember(EmitDefaultValue = false)]

For a boolean it will only emit the value if it is true.
For a nullable boolean it will only emit if it is not null.
For a string it will only emit the value if it isn't null.
For an int it will only emit the value if it isn't 0.

etc.

Make sure to put [DataContract] on the class itself and [DataMember] on all members you want serialized, whether you're specifying EmitDefaultValue or not.

Setting the EmitDefaultValue property to false is not a recommended practice. It should only be done if there is a specific need to do so (such as for interoperability or to reduce data size).

https://msdn.microsoft.com/en-us/library/system.runtime.serialization.datamemberattribute.emitdefaultvalue(v=vs.110).aspx

score 1 · Answer 5 · answered Dec 18 '13 at 08:02

1

You can use XmlElementAttribute.IsNullable:

[Serializable]
public class Result
{
    [XmlElement(IsNullable = true)]
    public DateTime? LastUpdated  { get; set; }
}

answered Dec 18 '13 at 08:02

Yochai Timmer

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It could not be used with attributes. It is only used fo elements. – Belurd Apr 05 '16 at 09:44
This does the opposite of what was asked. From [the documentation](https://learn.microsoft.com/en-us/dotnet/api/system.xml.serialization.xmlelementattribute.isnullable): "Gets or sets a value that indicates whether the XmlSerializer must serialize a member that is set to null as an empty tag with the xsi:nil attribute set to true." – Simon Morgan Mar 17 '23 at 09:15

How to ignore a nullable property from serialization if it is null or empty?

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