Ninject - define mapping in web.config file

Question

I'm using Ninject as the IoC container for my ASP.NET MVC app. What I'm currently doing is I have The following layers in my project:

• Core
• Factory
• Infrastructure
• Logic
• UI (ASP.NET MVC)

Infrastructure, Logic and UI all have references to Core and Factory has references to all.

When my ASP.NET application loads, I call a method in my Factory and pass it an enum value that tells it who runs it (UI or any other UI equivalent layer - for instance, I would like UI to work against Cache classes and Backoffice project to skip the Cache implementation of an interface and work directly against the database). The method then checks the enum and does the mapping in Ninject accordingly.

First off, is what I'm doing here is good practice? each layer doesn't know the layer next to it, and therefor loosely coupled. But on the other hand, the factory has references to all layers - which makes it tightly coupled.

Second, my mappings are hard coded in my Factory layer - what I would like to have is the mappings in a .config file (web.config) - is this possible?

Thanks

Answer 1

Inevitably, your solution will always have at least one project that everything else depends on. Otherwise, you could just break things out into separate solutions, because you'd have entirely separate applications. The goal is to remove duplication and create areas of responsibility; dependencies are a given.

As far as Ninject configuration goes, there is support for XML configuration. Unfortunately the docs are poorly designed and don't allow deep-linking, so I can't just simply give you a URL to go to. However, if you head over to http://www.ninject.org/wiki.html, and on the left, expand the "Ninject" heading, then "Using Ninject", and finally "Xml Configuration", you'll get the info you need.

Answer 2

Usually one should work with composition roots. The composition root (usually the UI) defines which bindings (mappings) are used and instanciates the object-graph in one go (well.. not always feasible but the goal is to be as close to this ideal as possible).

If i understand you correctly, you have replaced having multiple composition roots by having a factory with "enum" parameters. Probably so there's on single instance/layer responsible for mappings. The (preferred?!) alternative is to move this to the composition root, where you won't need an "switch(enum)". To reduce code duplication, put the shared bindings into a separate assembly or config file which you reuse. You might also want to look into NinjectModule's which can help you with that.

As far as ninject configuration by XML goes, i would recommend against that. It's far more brittle (renamings and the like). Only do it if you have mappings which you need to be able to modify after implementation. However, for most configuration issues it's entirely possible (and recommended) to do it differently. For example:

config file:

DatabaseProvider = MicrosoftSQL // OracleSQL if you want to use Oracle DB...

ninject binding:

Bind<IDatabaseProvider>().To<MicrosoftSqlDatabaseProvider>()
    .When(x => config.DatabaseProvier == "MicrosoftSQL");
Bind<IDatabaseProvider>().To<OracleSqlDtabaseProvider>()
    .When(x => config.DatabaseProvier == "OracleSQL");