Interfaces with Generics

[guimar86]

When an interface that uses generics is passed as dependency injection in a command it fails on the call as it requests the interfaces as if it is a parameter. Whereas with other interfaces this does not happen at all.

See the error message below:

[Arnab-Developer]

@guimar86 you have registered ICosmosDbRepository<CosmosDocumentBase> in the DI container. But you have injected ICosmosDbRepository<Document> in the AddCommand method. The generic type parameters (CosmosDocumentBase and Document) are not matching. This is the reason you are getting the error.

You need to design this differently to solve this problem. You can take a look at the below code.

using Cocona;
using Microsoft.Extensions.DependencyInjection;

var builder = CoconaApp.CreateBuilder();

builder.Services.AddTransient<ICosmosRepository<BaseDocument>, BaseDocumentRepository>();
builder.Services.AddTransient<ICosmosRepository<Document>, DocumentRepository>();

var app = builder.Build();

app.AddCommand("base-doc", async (ICosmosRepository<BaseDocument> repository) =>
{
    var doc = await repository.GetAsync();

    Console.WriteLine(doc.Id);
    Console.WriteLine(doc.Name);
});

app.AddCommand("doc", async (ICosmosRepository<Document> repository) =>
{
    var doc = await repository.GetAsync();

    Console.WriteLine(doc.Id);
    Console.WriteLine(doc.Name);
    Console.WriteLine(doc.Type);
});

await app.RunAsync();

internal record BaseDocument(int Id, string Name);

internal record Document(int Id, string Name, string Type) : BaseDocument(Id, Name);

internal interface ICosmosRepository<T>
{
    public Task<T> GetAsync();
}

internal interface IBaseDocumentRepository : ICosmosRepository<BaseDocument>;

internal class BaseDocumentRepository : IBaseDocumentRepository
{
    public async Task<BaseDocument> GetAsync()
    {
        var baseDocument = new BaseDocument(1, "doc1");
        var task = await Task.FromResult(baseDocument);
        return task;
    }
}

internal interface IDocumentRepository : ICosmosRepository<Document>;

internal class DocumentRepository : IDocumentRepository
{
    public async Task<Document> GetAsync()
    {
        var document = new Document(1, "doc1", "type1");
        var task = await Task.FromResult(document);
        return task;
    }
}