How to inject or use IConfiguration in Azure Function V3 with Dependency Injection when configuring a service

Question

Normally in a .NET Core project I would create a \'boostrap\' class to configure my service along with the DI registration commands. This is usually an extension method of

Answer 1

The linked example is poorly designed (In My Opinion). It encourages tight coupling and the mixing of async-await and blocking calls.

IConfiguration is added to the service collection by default as part of the start up, so I would suggest changing up your design to take advantage of the deferred resolution of dependencies so that the IConfiguration can be resolved via the built IServiceProvider using a factory delegate.

public static class BootstrapCosmosDbClient {

    private static event EventHandler initializeDatabase = delegate { };

    public static IServiceCollection AddCosmosDbService(this IServiceCollection services) {

        Func factory = (sp) => {
            //resolve configuration
            IConfiguration configuration = sp.GetService();
            //and get the configured settings (Microsoft.Extensions.Configuration.Binder.dll)
            CosmosDbClientSettings cosmosDbClientSettings = configuration.Get();
            string databaseName = cosmosDbClientSettings.CosmosDbDatabaseName;
            string containerName = cosmosDbClientSettings.CosmosDbCollectionName;
            string account = cosmosDbClientSettings.CosmosDbAccount;
            string key = cosmosDbClientSettings.CosmosDbKey;

            CosmosClientBuilder clientBuilder = new CosmosClientBuilder(account, key);
            CosmosClient client = clientBuilder.WithConnectionModeDirect().Build();
            CosmosDbService cosmosDbService = new CosmosDbService(client, databaseName, containerName);

            //async event handler
            EventHandler handler = null;
            handler = async (sender, args) => {
                initializeDatabase -= handler; //unsubscribe
                DatabaseResponse database = await client.CreateDatabaseIfNotExistsAsync(databaseName);
                await database.Database.CreateContainerIfNotExistsAsync(containerName, "/id");
            };
            initializeDatabase += handler; //subscribe
            initializeDatabase(null, EventArgs.Empty); //raise the event to initialize db

            return cosmosDbService;
        };
        services.AddSingleton(factory);
        return service;
    }
}

Note the approach taken to get around the having to use async void in a non-async event handler.

Reference Async/Await - Best Practices in Asynchronous Programming.

So now the Configure can be properly invoked.

public class Startup : FunctionsStartup {

    public override void Configure(IFunctionsHostBuilder builder) =>
        builder.Services
            .AddHttpClient()
            .AddCosmosDbService();
}