What data type should I use for an Image in my domain model?

Question

I am using Silverlight with a DDD approach. I have a Person domain object that has properties such as FirstName, LastName, Address, etc. The Person needs to have an Image.

What is the best way to handle this?

I don't really want to put an Windows.Controls.Image property on the Person object because this it will be coupled to Silverlight/WPF and I might want to use this object with some other technology in the future (ASP, WinForms, the next new thing, etc).

I also need to be able to save and load the image somewhere. Is it best practice to save the image to a database or to a file system? I am currently using nHibernate with Microsoft SQL Server, but I also want to be able to support nHibernate with mySql and possibly some other databases. It is also possible that I may some day want to replace nHibernate with entity framework or some other technology (I am abstracting this out using a repository).

Given this information, how should I handle Images for my Person?

Answer 1

Well, byte[] (or something wrapping a byte[]) is fairly portable... most anything else is going to be implementation specific.

Re database vs file... for the purposes of the client apps (Silverlight, WPF, etc) I would probably expose them via a web page rather than a WCF (etc) call - i.e. some ASP.NET handler (or ASP.NET MVC route) that returns the image via an http call. Then all you actually need in the client is the path to the image (/people/images/12345 or whatever).

For storage - either is usually fine... in SQL Server 2008 you can do both at once with the file-stream type. One of the problems with storing BLOBs in the database is increasing the size, but a few (small) images won't usually hurt (unless you are using SQL Express and have a capped db size). But using the database has the advantage that a single backup includes everything.

Saying that, though: almost every implementation I've done like this has used files.

Answer 2

Are you actually using the binary blob for anything? If not, pass around a reference to something on the filesystem. I'd be worried about pissing things off if you start carrying around byte[]'s or something.

If you are WPF, everything takes a URI as an ImageSource:

BitmapImage pic = new BitmapImage(new Uri("YourAssembly;components/images/something.jpg"));

Keep in mind that if you go my suggested route and move this to Silverlight, you'll need a crossdomain.xml file on the domain you are dishing these things out.

If you do need to mess with the binary blob, then keep all that as a Stream of some form and have your Person.Image class offer a way to get a StreamReader/StreamWriter like GetImageStream(). Then your database stuff can get a StreamReader and go write that stuff into the database. Without checking, my guess is just about every database out there that has binary blobs writes out using a Stream, not byte[].

...Just some thoughts. Dont forget BitmapImage lets you tap into its Stream too, but you'll have to look that up in the docs :-) Hope that helps.