.Net core Dependency injection - with parameters

Question

NOTE: This example has been simplified

I have got a Client's Contact table and wanted to retrieve specific client contact information from DB. The code I typed belove brings me all contact details. I wanted to use a parameter to only bring me specific client contacts.

I used IClientContactRepository interface like this

public interface IClientContactRepository
{
    IQueryable<ClientContactModel> ClientContacts { get; }
}

And i used this class to retrive data from database with dapper

public class ClientContactRepository : IClientContactRepository
{
    private readonly IConfiguration configuration;
    private List<ClientContactModel> ClientContactList {get;set;}


    public ClientContactRepository(IConfiguration config)
    {
        configuration = config;

        SqlConnection conn = new SqlConnection(configuration["ConnectionString"]);

        using (var connection = conn)
        {
            ClientContactList = connection.Query<ClientContactModel>("Select * FROM ContactTable ").ToList();
        }
    }
    public IQueryable<ClientContactModel> ClientContacts => ClientContactList;
}

In my Startup class

  services.AddTransient<IClientContactRepository, ClientContactRepository>();

My QUESTION is: can I pass the client's id parameter to the constructor.

I tried this: add a parameter to the constructor

  public ClientContactRepository(IConfiguration config, int clientId)

and tried to start up class.

 services.AddTransient<IClientContactRepository, ClientContactRepository(int,i)>()

Didn't work.... Can someone help me how to pass parameter please?

Answer 1

Yes, but where are you getting the client ID from - is it a configured value that will be static for the lifetime of the application? If so, you can use the AddTansient method overload that accepts a factory delegate to create the objects.

The better way (will cover all use cases) is registering the type that can provide that information (create one if no such type exists) with the DI container and use that as a parameter in the constructor of your repo.

As an example, let’s say you get your client ID from a claim, so the type you need to inject is IPrincipal:

services.AddScoped<IPrincipal>(
    provider => provider.GetService<IHttpContextAccessor>()
        .HttpContext
        .User);

You would then inject the IPrincipal into your repo constructor and retrieve the client ID. An even better way would be to create your own type “ClientIdAccessor” which is responsible for providing the client ID. You would then not have a dependency on IPrincipal when testing your repo and the implementation of this new type would only depend on external libraries for your asp.net core implementation.

Side note: are you certain you want to use AddTransient for your repo? Usually you’d want to use the same repo object for the lifetime of the request (I.e. AddScoped).