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Interoperable object references

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By default, DataContractSerializer serializes objects by value. You can use the IsReference property to instruct the data contract serializer to preserve object references when serializing objects.

Generated XML

As an example, consider the following object:

[DataContract]  
public class X  
{  
    SomeClass someInstance = new SomeClass();  
    [DataMember]  
    public SomeClass A = someInstance;  
    [DataMember]  
    public SomeClass B = someInstance;  
}  
  
public class SomeClass
{  
}

With PreserveObjectReferences set to false (the default), the following XML is generated:

<X>  
   <A>contents of someInstance</A>  
   <B>contents of someInstance</B>  
</X>

With PreserveObjectReferences set to true, the following XML is generated:

<X>  
   <A id="1">contents of someInstance</A>  
   <B ref="1"></B>  
</X>

However, XsdDataContractExporter doesn't describe the id and ref attributes in its schema, even when the preserveObjectReferences property is set to true.

Using IsReference

To generate object reference information that's valid according to the schema that describes it, apply the DataContractAttribute attribute to a type, and set the IsReference flag to true. The following example modifies class X in the previous example by adding IsReference:

[DataContract(IsReference=true)]
public class X
{  
     SomeClass someInstance = new SomeClass();
     [DataMember]
     public SomeClass A = someInstance;
     [DataMember]
     public SomeClass B = someInstance;
}
  
public class SomeClass
{
}

The generated XML is as follows:

<X>  
    <A id="1">
        <Value>contents of A</Value>  
    </A>
    <B ref="1"></B>  
</X>

Using IsReference ensures compliance on message round-tripping. Without it, when a type is generated from schema, the XML output for that type isn't necessarily compatible with the schema originally assumed. In other words, although the id and ref attributes were serialized, the original schema could have barred these attributes (or all attributes) from occurring in the XML. With IsReference applied to a data member, the member continues to be recognized as referenceable when round-tripped.

See also