A new feature in DD4T is the Web library (DD4T.Web.dll). It contains some functions that are useful in any .NET web site, whether they use MVC or not. It offers – for example – a way to serve binaries (images, PDFs, etc) straight out of the broker database.
Why would you want to do that, might you ask? Of course, Tridion has been used for ages to deliver binaries directly to the file system. Binaries are rarely dynamic in nature, so storing them as static files is actually a good idea!
Well, yes and no. Yes, storing binaries on the file system is great for performance, but it has a big downside: you cannot just plug in a new server into your web farm anymore, since it would not contain these binary files. Also, your developers who are so used to running the entire web app from within their IDE, would miss out on the images if they are only published to a central presentation environment.
If you work with DD4T, that does not mean you MUST serve the binary files from the broker database. It is okay to serve them from the file system as well!
Serving binaries with the BinaryDistributionModule
The DD4T.Web library contains a BinaryDistributionModule. Purpose of this HttpModule is to make sure the requested binary is available on the file system, so IIS can serve it. Here’s how it works:
- If the binary is not on the file system, it is retrieved from the broker database and stored as a file
- If the binary is already on the file system, the timestamp of the file is compared against the last publish date of the binary in the broker database. If the file is stale, it is replaced. If the binary is no longer present in the broker, the file is removed (resulting in a 404, which is what you would expect if you attempt to view a file which has been unpublished).
To configure the BinaryDistributionModule, add the following XML code to the system.webServer node in your Web.config:
<modules runAllManagedModulesForAllRequests="true">
<add name="BinaryModule"
type="DD4T.Web.Binaries.BinaryDistributionModule" />
</modules>
Good stuff. Note that if the binary on the file system is not updated, even though you have changed and re-published it, you can try installing hotfix CD_2011.1.1.84845 (this is for 2011 SP1-1 and earlier – later versions do not need this). This fixes an issue where the last published date for binaries is not updated on republish, which means the BinaryDistributionModule cannot tell when the version it has saved to the filesystem should be updated or not.