Version Tolerant Serialization
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Fields can be marked as optional by applying the OptionalFieldAttribute attribute to them. During deserialization, if the optional data is missing, the serialization engine ignores the absence and does not throw an exception. Thus, applications that expect older versions of a type can send data to applications that expect newer versions of the same type.
The following example shows version 2.0 of the Address class with the CountryField field marked as optional. If an older application sends version 1 to a newer application that expects version 2.0, the absence of the data is ignored.
Serialization callbacks are a mechanism that provides hooks into the serialization/deserialization process at four points.
Attribute
When the Associated Method is Called
Typical Use
OnDeserializingAttribute
Before deserialization.*
Initialize default values for optional fields.
OnDeserializedAttribute
After deserialization.
Fix optional field values based on contents of other fields.
OnSerializingAttribute
Before serialization.
Prepare for serialization. For example, create optional data structures.
OnSerializedAttribute
After serialization.
Log serialization events.
* This callback is invoked before the deserialization constructor, if one is present.
// Version 1 of the Address class.
[Serializable]
public class Address
{
public string Street;
public string City;
}
// Version 2.0 of the Address class.
[Serializable]
public class Address
{
public string Street;
public string City;
// The older application ignores this data.
public string CountryField;
}Fields can be marked as optional by applying the OptionalFieldAttribute attribute to them. During deserialization, if the optional data is missing, the serialization engine ignores the absence and does not throw an exception. Thus, applications that expect older versions of a type can send data to applications that expect newer versions of the same type.
The following example shows version 2.0 of the Address class with the CountryField field marked as optional. If an older application sends version 1 to a newer application that expects version 2.0, the absence of the data is ignored.
[Serializable]
public class Address
{
public string Street;
public string City;
[OptionalField]
public string CountryField;
}Serialization callbacks are a mechanism that provides hooks into the serialization/deserialization process at four points.
Attribute
When the Associated Method is Called
Typical Use
OnDeserializingAttribute
Before deserialization.*
Initialize default values for optional fields.
OnDeserializedAttribute
After deserialization.
Fix optional field values based on contents of other fields.
OnSerializingAttribute
Before serialization.
Prepare for serialization. For example, create optional data structures.
OnSerializedAttribute
After serialization.
Log serialization events.
* This callback is invoked before the deserialization constructor, if one is present.
[Serializable]
public class Address
{
public string Street;
public string City;
[OptionalField]
public string CountryField;
[OnDeserializing]
private void SetCountryRegionDefault (StreamingContext sc)
{
CountryField = "Japan";
}
}