具有向后兼容性的Xml阅读

Question

The XML that i am currently working is directly formed using XML serializer (Serializing Class and its nested counter parts)

Also if there is an addition of a new Property is directly handled by the serializer but the problem comes when there is a deletion of property (value Type) or removal of and entire class or addition of class

I wish to read the old as well as the new XML files.... I cant seem to figure out how..

Process

Some ways

But i don't think these are good for a maintainable code

1) Make the custom XML parser (this will be less flexible as every time the change is done the parser has to be updated and hence tested again).
2) Use multiple Models then migrate from old to new (Taking essential components)
3) Export Old file and import the new file (This will also require another XML file and may b related to point 2)
4) Any other means (Please suggest)

I am not well versed with XML and its versioning. Also is XML a good choice for this or Any other file type/DB that i can use in place of XML

Any help in this regard would be helpful.

Answer 1

I usually follow your solution "#2" where I namespace version my models (Myapp.Models.V1.MyModel), this way you can maintain backward compatibility with clients still using the older schema (or in your case, loading an older file).

As suggested in the comments, you can use a simple attribute on the root node to determine the version, and use either xmlreader, or even a simple regex on the first line of the file to read the version number.

As far as your second question, about file type/db, depending on your needs, I would highly recommend looking at a document database like MongoDB or RavenDB, as implementation is straightforward/simple, and does not require the use of an ORM tool like entity framework to handle proper separation of concerns. If you need something portable, in the cases such as desktop app "save file", SqlLite is a good file based databases, but you will likely want to use an ORM for mapping your model to your database.

Links:

• MongoDB: http://www.mongodb.org/
• RavenDB: http://ravendb.net/
• Sqllite: http://www.sqlite.org/

Answer 2

In most ways, XmlSerializer already has pretty good version support built in. In most cases, if you add or remove elements it isn't a problem: extra (unexpected) data will be silently ignored - or put into the [XmlAnyElement] / [XmlAnyAttribute] member (if one) for round-trip. Any missing data just won't be initialized. The only noticeable problem is with sub-types, but adding and removing sub-types (or entire types) is going to be fairly fundamental to any serializer. One common option in the case of sub-types is: use a single model, but just don't remove any sub-types (adding sub-types is fine, assuming you don't need to be forwards compatible). However if this is not possible, the multiple models (model per revision) is not a bad approach.