Serialization and object versioning
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If I want to serialize an object I have to use [Serializable] attribute and all member variables will be written to the file. What I don't know how to do versioning e.g. if I add a new member variable (rename a variable or just remove a variable) to the object e.g. m_dRadius and then I open (deserialize) the file how can I determine that the variable was initialized during the load or not. I know that there are version tolerant approaches and I can mark variables with [OptionalField(VersionAdded = 1)] attribute. If I open an old file the framework will ignore this optional (new variable) and it will be just zero/null. But again how can I determine if the variable is initialized by load to zero or it was ignored. I can write the class/object version number to the stream. Use the ISerializable approach and in the constructor(SerializationInfo oInfo, StreamingContext context) method read this version number. This will exactly tell me what is the class version in the stream. However I expected that such kind of versioning is already implemented by the streaming framework. I tried to obtain the Assembly version from the SerializationInfo but it is always set to current version not to the version which was used when the object was saved. What is the preferred approach? I found a lot of articles on the net, but I could not find a good solution for this... Any help is appreciated :-) Thanks, Abyss
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If I want to serialize an object I have to use [Serializable] attribute and all member variables will be written to the file. What I don't know how to do versioning e.g. if I add a new member variable (rename a variable or just remove a variable) to the object e.g. m_dRadius and then I open (deserialize) the file how can I determine that the variable was initialized during the load or not. I know that there are version tolerant approaches and I can mark variables with [OptionalField(VersionAdded = 1)] attribute. If I open an old file the framework will ignore this optional (new variable) and it will be just zero/null. But again how can I determine if the variable is initialized by load to zero or it was ignored. I can write the class/object version number to the stream. Use the ISerializable approach and in the constructor(SerializationInfo oInfo, StreamingContext context) method read this version number. This will exactly tell me what is the class version in the stream. However I expected that such kind of versioning is already implemented by the streaming framework. I tried to obtain the Assembly version from the SerializationInfo but it is always set to current version not to the version which was used when the object was saved. What is the preferred approach? I found a lot of articles on the net, but I could not find a good solution for this... Any help is appreciated :-) Thanks, Abyss
Abyss wrote:
What is the preferred approach?
If there was a preferred approach that applies in all circumstances, all other approaches would be dropped. I'd go for the simplest solution; meaning the OptionalField if I'd expect that the class is not going to change much. Anything that could have more/complexer versions, I'd write a custom ISerializable.
Abyss wrote:
However I expected that such kind of versioning is already implemented by the streaming framework. I tried to obtain the Assembly version from the SerializationInfo but it is always set to current version not to the version which was used when the object was saved.
It'd be overkill, and not everybody will be wanting to use those version-numbers. Keep in mind that the version-number you see is the one of the assembly that the class is contained in. Alternatively, one might use different version numbers for files, created with a single version of a class. So, the one-size-fits all wouldn't fit here.
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