如何使用依赖注入将参数传递给DbContext构造函数

Question

I'm in the middle of reworking my DbContext to support Multitenancy by requiring a tenantId:

public AppContext(int tenantId)            
    {
        _tenantId = tenantId;
    }

Before, there was no parameter.

In my service classes, I have the context instantiated with DI:

    private readonly AppContext db;
    private CommService _commService;

    public AdminService(AppContext db, CommService commService)
    {
        this.db = db;
        _commService = commService;
    }

And in my Controllers, the same thing:

    private readonly CommService _commService;
    public AdminController(CommService commService) {
         _commService = commService;
    }

I'm using Unity, but haven't really done much configuration at all - it all just works.

I'll be retrieving the tenantId from my Controllers. How do I go about passing the tenantId from Controller > Service layer > Constructor?

Answer 1

Unity can't pass the tenantId as this is a variable which will depend on the current use for example or any other condition, the tenantId will be determined at runtime, so don't make it injectable.

Still, you can make a factory for it and injecet this factory.

ex:

public Interface ITenantDiscovery
{
  int TenantId{get;}
}

public class UrlTenantDiscovery:ITenantDiscovery
{
 public int TenantId
 {
   get
    {
       var url = -- get current URL, ex: from HttpContext
       var tenant = _context.Tenants.Where(a=>a.Url == url);
       return tenant.Id; -- cache the Id for subsequent calls
    }
 }

In UnityConfig, register the ITenantDiscovery and its implementation UrlTenantDiscovery

Change your AppContext to accept an instance of ITenantDiscovery

public AppContext(ITenantDiscovery tenantDiscovery)            
    {
        _tenantId = tenantDiscovery.TenantId;
    }

That is it.