如何使用异步方法在 DI 中创建 Cosmos 客户端？

Question

I want to use Cosmos DB in my ASP.net 5 WebAPI project. To create the client I want to use Dependency injection to inject it to my Service. To do so I created this statement in my public void ConfigureServices(IServiceCollection services)

services.AddSingleton(async s => {
    var dbConfig = Configuration.GetSection("Database");
    var conn = dbConfig["ConnectionString"];
    var dbName = dbConfig["DbName"];
    if (string.IsNullOrEmpty(conn))
    {
       throw new ConfigurationErrorsException();
    }
    var client = new CosmosClient(conn);
    await client.CreateDatabaseIfNotExistsAsync(dbName);
    return client;
});

But in this case I get an error in my service when I try to inject it via:

public ProductService(ILogger<ProductService> logger, CosmosClient client)
{
    this._client = client;
    _logger = logger;
}

Because my arrow function returns Task<CosmosClient> instead of CosmosClient . But how can I change that therefore Database-creation methos is async and I have to use await?!

THanks

Answer 1

Microsoft's Dependency Injection does not support async .

I recommend having a separate "schema deployer" project that is run as part of your deployment (or locally to create databases on the emulator). Then you can remove the CreateDatabaseIfNotExistsAsync call and inject CosmosClient .

If you must use CreateDatabaseIfNotExistsAsync from within your application (and not during deployment), then you will need to inject an asynchronous factory :

public sealed class CosmosClientFactory
{
  private readonly Lazy<Task<CosmosClient>> _lazy;

  public CosmosClientFactory(Configuration configuration)
  {
    _lazy = new(async () =>
    {
      var dbConfig = configuration.GetSection("Database");
      var conn = dbConfig["ConnectionString"];
      var dbName = dbConfig["DbName"];
      if (string.IsNullOrEmpty(conn))
      {
       throw new ConfigurationErrorsException();
      }
      var client = new CosmosClient(conn);
      await client.CreateDatabaseIfNotExistsAsync(dbName);
      return client;
    });
  }

  public Task<CosmosClient> CreateAsync() => _lazy.Value;
}

Usage:

private readonly CosmosClientFactory _clientFactory;
public ProductService(ILogger<ProductService> logger, CosmosClientFactory clientFactory)
{
  _clientFactory = clientFactory;
  _logger = logger;
}
public async Task DoSomethingAsync()
{
  var client = await _clientFactory.CreateAsync();
  await client.DoSomethingAsync();
}