C# – versioning serialized files

c++design-patternsserialization

I've got a working app that serializes a document (of type IDocument) to disk. From there there's another app that I've made that can open that document (IDocument implements IPrintDocument) for viewing.

Let's assume that I've written an IDocument to disk, and then a week later a field gets added to the IDocument object. Both the program that writes the files and the one that opens them are updated with this new 'version' of IDocument. It will then break (I assume – haven't had a chance to check, I'm looking ahead here) when trying to open the previous IDocument version. Is there a known pattern that alleviates this kind of problem?

Best Solution

Yes - use a serialization mechanism which is tolerant to versioning.

Predictably enough, I'm going to suggest using Google's Protocol Buffers, for which there are at least two viable .NET implementations. So long as you're careful, Protocol Buffers are both backward and forward compatible - you can read a new message with old code and vice versa, and the old code will still be able to preserve the information it doesn't understand.

Another alternative is XML, whether using .NET's built-in XML serialization or not. The built-in serialization isn't particularly flexible in terms of versioning as far as I'm aware.

Related Solutions

C# – How to delete all files and folders in a directory

System.IO.DirectoryInfo di = new DirectoryInfo("YourPath");

foreach (FileInfo file in di.GetFiles())
{
    file.Delete(); 
}
foreach (DirectoryInfo dir in di.GetDirectories())
{
    dir.Delete(true); 
}

If your directory may have many files, EnumerateFiles() is more efficient than GetFiles(), because when you use EnumerateFiles() you can start enumerating it before the whole collection is returned, as opposed to GetFiles() where you need to load the entire collection in memory before begin to enumerate it. See this quote here:

Therefore, when you are working with many files and directories, EnumerateFiles() can be more efficient.

The same applies to EnumerateDirectories() and GetDirectories(). So the code would be:

foreach (FileInfo file in di.EnumerateFiles())
{
    file.Delete(); 
}
foreach (DirectoryInfo dir in di.EnumerateDirectories())
{
    dir.Delete(true); 
}

For the purpose of this question, there is really no reason to use GetFiles() and GetDirectories().

Php – Check to see if a string is serialized

I'd say, try to unserialize it ;-)

Quoting the manual :

In case the passed string is not unserializeable, FALSE is returned and E_NOTICE is issued.

So, you have to check if the return value is false or not (with === or !==, to be sure not to have any problem with 0 or null or anything that equals to false, I'd say).

Just beware the notice : you might want/need to use the @ operator.

For instance :

$str = 'hjkl';
$data = @unserialize($str);
if ($data !== false) {
    echo "ok";
} else {
    echo "not ok";
}

Will get you :

not ok

EDIT : Oh, and like @Peter said (thanks to him!), you might run into trouble if you are trying to unserialize the representation of a boolean false :-(

So, checking that your serialized string is not equal to "b:0;" might be helpful too ; something like this should do the trick, I suppose :

$data = @unserialize($str);
if ($str === 'b:0;' || $data !== false) {
    echo "ok";
} else {
    echo "not ok";
}

testing that special case before trying to unserialize would be an optimization -- but probably not that usefull, if you don't often have a false serialized value.

Best Solution

Related Solutions

C# – How to delete all files and folders in a directory

Php – Check to see if a string is serialized

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