c# - Circular Reference when using XML Serialization?

Question

I am receiving the following exception when trying to serialize an object using XMLSerialization.

A circular reference was detected while serializing an object of type MyObject}

I know the circular reference is because ObjectA can have a childObject of ObjectB and ObjectB's parentObject is ObjectA, however I would like to keep that reference if possible . Is there a way to get this object to serialize with XML Serialization without losing any data during the serialization process? I'm not very familar with serialization so I'm hoping theres some kind of Attribute I could set.

Answer 1

There are several options depending on serializer type.

If you could use DataContractSerializer or BinaryFormatter then you may use OnSerializedAttribute and set Parent property for your child object to this:

[Serializable]
public class Child
{
    public string Foo { get; set; }

    public Parent Parent { get { return parent; } set { parent = value; } }

    // We don't want to serialize this property explicitly.
    // But we could set it during parent deserialization
    [NonSerialized]
    private Parent parent;
}

[Serializable]
public class Parent
{
    // BinaryFormatter or DataContractSerializer whould call this method
    // during deserialization
    [OnDeserialized()]
    internal void OnSerializedMethod(StreamingContext context)
    {
        // Setting this as parent property for Child object
        Child.Parent = this;
    }

    public string Boo { get; set; }

    public Child Child { get; set; }
}

class Program
{
    static void Main(string[] args)
    {
        Child c = new Child { Foo = "Foo" };
        Parent p = new Parent { Boo = "Boo", Child = c };

        using (var stream1 = new MemoryStream())
        {
            DataContractSerializer serializer = new DataContractSerializer(typeof (Parent));
            serializer.WriteObject(stream1, p);
            stream1.Position = 0;
            var p2 = (Parent)serializer.ReadObject(stream1);

            Console.WriteLine(object.ReferenceEquals(p, p2)); //return false
            Console.WriteLine(p2.Boo); //Prints "Boo"

            //Prints: Is Parent not null: True
            Console.WriteLine("Is Parent not null: {0}", p2.Child.Parent != null);
        }
    }

}

If you want to use XmlSerializer you should implement IXmlSerializable, use XmlIgnoreAttribute and implemented more or less the same logic in ReadXml method. But in this case you should also implement all Xml serialization logic manually:

[Serializable]
public class Child
{
    public Child()
    {
    }

    public string Foo { get; set; }

    [XmlIgnore]
    public Parent Parent { get; set; }
}

[Serializable]
public class Parent
{
    public Parent()
    {
    }

    #region IXmlSerializable Members

    public System.Xml.Schema.XmlSchema GetSchema()
    {
        throw new NotImplementedException();
    }

    public void ReadXml(System.Xml.XmlReader reader)
    {
        //Reading Parent content
        //Reading Child
        Child.Parent = this;
    }

    public void WriteXml(System.Xml.XmlWriter writer)
    {
        //Writing Parent and Child content
    }

    #endregion

    public string Boo { get; set; }

    public Child Child { get; set; }
}