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POBest practice for protobuf-net, versioning and surrogate types
 

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  1. POBest practice for protobuf-net, versioning and surrogate types
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    <p>I'm trying to determine how to address this use case using protobuf-net (Marc Gravell's implementation).</p> <ul> <li>We have class A, which is considered version 1</li> <li>An instance of class A has been serialized to disk</li> <li>We now have class B, which is considered version 2 of class A (there were so many things wrong with class A, we had to create class B for the next version). Class A still exists in code, but only for legacy purposes.</li> <li>I want to deserialize the version:1 data (stored to disk) as a class B instance, and use a logic routine to translate the data from the previous class A instance to a new instance of class B.</li> <li>The instance of class B will be serialized to disk during operation.</li> <li>The application should expect to deserialize instances of both class A and B.</li> </ul> <p>The concept of data contract surrogates and the DataContractSerializer come to mind. The goal is transition the version:1 data to the new class B structure.</p> <p>An example:</p> <pre><code>[DataContract] public class A { public A(){} [DataMember] public bool IsActive {get;set;] [DataMember] public int VersionNumber { get { return 1; } set { } } [DataMember] public int TimeInSeconds {get;set;} [DataMember] public string Name {get;set;} [DataMember] public CustomObject CustomObj {get;set;} //Also a DataContract [DataMember] public List&lt;ComplexThing&gt; ComplexThings {get;set;} //Also a DataContract ... } [DataContract] public class B { public B(A a) { this.Enabled = a.IsActive; //Property now has a different name this.TimeInMilliseconds = a.TimeInSeconds * 1000; //Property requires math for correctness this.Name = a.Name; this.CustomObject2 = new CustomObject2(a.CustomObj); //Reference objects change, too this.ComplexThings = new List&lt;ComplexThings&gt;(); this.ComplexThings.AddRange(a.ComplexThings); ... } public B(){} [DataMember] public bool Enabled {get;set;] [DataMember] public int Version { get { return 2; } set { } } [DataMember] public double TimeInMilliseconds {get;set;} [DataMember] public string Name {get;set;} [DataMember] public CustomObject2 CustomObject {get;set;} //Also a DataContract [DataMember] public List&lt;ComplexThing&gt; ComplexThings {get;set;} //Also a DataContract ... } </code></pre> <p>Class A was the first iteration of our object, and is actively in use. Data exists in v1 format, using class A for serialization.</p> <p>After realizing the error of our ways, we create a new structure called class B. There are so many changes between A and B that we feel it's better to create B, as opposed to adapting the original class A.</p> <p>But our application already exists and class A is being used to serialize data. We're ready to roll our changes out to the world, but we must first deserialize data created under version 1 (using class A) and instantiate it as class B. The data is significant enough that we can't just assume defaults in class B for missing data, but rather we must transition the data from a class A instance to class B. Once we have a class B instance, the application will serialize that data again in class B format (version 2).</p> <p>We're assuming we'll make modifications to class B in the future, and we want to be able to iterate to a version 3, perhaps in a new class "C". We have two goals: address data already in existence, and prepare our objects for future migration.</p> <p>The existing "transition" attributes (OnSerializing/OnSerialized,OnDeserializing/OnDeserialized,etc.) don't provide access to the previous data.</p> <p>What is the expected practice when using protobuf-net in this scenario?</p>
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      1. USFabian Tamp
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    1. COdo you know in advance whether you are reading v1 vs v2 data? how different are v1 & v2? on your 4th bullet - why would you read v1 data into a B, rather than read it into an A then convert the A to a B?
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      1. USMarc Gravell
    2. COI won't know it. To expand upon this, I have to assume that I may encounter V1, V2, V3, V4, etc. And the difference could be substantial -- think replacement of entire sets of classes.
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    3. CO"why would you read v1 data into a B, rather than read it into an A then convert the A to a B" - definitely want to do this, but I won't know if it's A or B data ahead of time.
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