在WebApi应用程序中将MEF与DI结合使用

Question

I'm planning on using MEF to implement a plugin architecture for my import plugins. These plugins will import various data into the db (eg. customers, addresses, products, etc).

The import plugin class looks like this:

public interface IImportPlugin
{
    string Name { get; }
    void Import();
}

[Export(typeof(IImportPlugin))]
public class ImportCustomers : IImportPlugin
{
    private readonly ICustomerService customerService;

    public string Name
    {
        get { this.GetType().Name; }
    }

    public ImportCustomers(ICustomerService _customerService) 
    {
        customerService = _customerService;
    }

    public void Import() {}
}

I then have a controller, which first gets all import plugins as follows:

public IHttpActionResult GetImportPlugins()
{
    var catalog = new AggregateCatalog();

    catalog.Catalogs.Add(new DirectoryCatalog(Path.Combine(AppDomain.CurrentDomain.BaseDirectory, "bin")));

    var directoryCatalog = new DirectoryCatalog(Path.Combine(AppDomain.CurrentDomain.BaseDirectory, "Plugins"));
    catalog.Catalogs.Add(directoryCatalog);

    var container = new CompositionContainer(catalog);
    container.ComposeParts();

    var list = container.GetExportedValues<IImportPlugin>().Select(x => x.Name);
    return Ok(list);
}

The import plugin needs to reference my Services assembly because this is where the BL takes place. I register my services in the main WebApi project with Autofac as follows:

builder.RegisterAssemblyTypes(assemblies)
  .Where(t => t.Name.EndsWith("Service"))
  .AsImplementedInterfaces()
  .InstancePerRequest();

Is it possible to pass different services to different import plugins?

For example, if I'm importing products I need to pass the ProductService , and if I'm importing customers I might need to pass CustomerService and AddressService .

How can I inject these services inside the plugins (through their constructors just like one would do in a controller)?

Answer 1

For plugin-like architecture, you need three things:

• Contracts (basicaly assembly containing only interfaces and simple objects withouth BL). This will be used as API for your plugins. Also, here you can specify IImportPlugin interface.

• Module which responsibily will be loading plugin modules from some folder, or from somewhere else.

• Module in each plugin you create, to register your plugin as IImportPlugin inside DI container.

You can register your plugin modules like this in loop:

builder.RegisterAssemblyModules(/*plugin 'Assembly' goes here*/);

In your plugin assembly, in specific module, you specify only your plugin registration:

public class MyPluginModule : Module
{
    protected override void Load(ContainerBuilder builder)
    {
        builder.Register<ImportCustomers>().As<IImportPlugin>();
    }
}

Then in plugin implementation ImportCustomer you can use everything from Contract assembly (for example your ICustomerService interface). And if your system registered dependecies for your plugin - it will succesfuly load into DI container.