I have an idea for how to solve this problem, but I wanted to know if there’s something easier and more extensible to my problem.
The program I’m working on has two basic forms of data: images, and the information associated with those images. The information associated with the images has been previously stored in a JET database of extreme simplicity (four tables) which turned out to be both slow and incomplete in the stored fields. We’re moving to a new implementation of data storage. Given the simplicity of the data structures involved, I was thinking that a database was overkill.
Each image will have information of it’s own (capture parameters), will be part of a group of images which are interrelated (taken in the same thirty minute period, say), and then part of a larger group altogether (taken of the same person). Right now, I’m storing people in a dictionary with a unique identifier. Each person then has a List of the different groups of pictures, and each picture group has a List of pictures. All of these classes are serializable, and I’m just serializing and deserializing the dictionary. Fairly straightforward stuff. Images are stored separately, so that the dictionary doesn’t become astronomical in size.
The problem is: what happens when I need to add new information fields? Is there an easy way to setup these data structures to account for potential future revisions? In the past, the way I’d handle this in C was to create a serializable struct with lots of empty bytes (at least a k) for future extensibility, with one of the bytes in the struct indicating the version. Then, when the program read the struct, it would know which deserialization to use based on a massive switch statement (and old versions could read new data, because extraneous data would just go into fields which are ignored).
Does such a scheme exist in C#? Like, if I have a class that’s a group of String and Int objects, and then I add another String object to the struct, how can I deserialize an object from disk, and then add the string to it? Do I need to resign myself to having multiple versions of the data classes, and a factory which takes a deserialization stream and handles deserialization based on some version information stored in a base class? Or is a class like Dictionary ideal for storing this kind of information, as it will deserialize all the fields on disk automatically, and if there are new fields added in, I can just catch exceptions and substitute in blank Strings and Ints for those values?
If I go with the dictionary approach, is there a speed hit associated with file read/writes as well as parameter retrieval times? I figure that if there’s just fields in a class, then field retrieval is instant, but in a dictionary, there’s some small overhead associated with that class.
Thanks!
My brain is fried at the moment, so I’m not sure I can advise for or against a database, but if you’re looking for version-agnostic serialization, you’d be a fool to not at least check into Protocol Buffers.
Here’s a quick list of implementations I know about for C#/.NET: