How To integrate Dependency Injection In Azure Functions

First, we need to install the below Nuget package into the Azure function project.

To inject dependency we first need to create a new class called "Startup. cs" into the root of the project. Add the below code into the class which is used at the start of the function app.

using AzureFuncDependencyDemo;
using AzureFuncDependencyDemo.Customer.Service;
using Microsoft.Azure.Functions.Extensions.DependencyInjection;
using Microsoft.Extensions.DependencyInjection;
[assembly: FunctionsStartup(typeof(Startup))]
namespace AzureFuncDependencyDemo
{
    public class Startup : FunctionsStartup
    {
        public override void Configure(IFunctionsHostBuilder builder)
        {
            builder.Services.AddTransient<ICustomerService, CustomerService>();
        }
    }
}

• Then FunctionStartup attribute is used to register the assembly which specifies the name you need to use during the startup of the function.
• Initiate FunctionStartup and implement the Configure method to register all the dependencies.
• Register ICustomerService dependency in the same way we usually do in ASP.NET core apps.

Now add the below code into the function to inject dependency and get the customer data.

using System.Threading.Tasks;
using AzureFuncDependencyDemo.Customer.Service;
using Microsoft.AspNetCore.Http;
using Microsoft.AspNetCore.Mvc;
using Microsoft.Azure.WebJobs;
using Microsoft.Azure.WebJobs.Extensions.Http;
namespace AzureFuncDependencyDemo
{
    public class Function1
    {
        private readonly ICustomerService customerService;

        public Function1(ICustomerService _customerService)
        {
            customerService = _customerService;
        }
        [FunctionName("Function1")]
        public async Task<IActionResult> Run(
            [HttpTrigger(AuthorizationLevel.Anonymous, "get", Route = null)] HttpRequest req)
        {
            var customersData = await customerService.GetCustomersDataAsync();
            return new OkObjectResult(customersData);
        }
    }
}

Now to run the function app we need to just run the project. It will then start Azure function cli to run the function.

The function is running on 'http://localhost:7071/api/Function1'.

That's it. We have now configured dependency injection into the Azure function app.

If we want to use HttpClient to make an HTTP request then we can inject the HttpClient dependency in the same way we like adding it into NET Core. So let's add the below Nuget package,

After that open Startup.cs class and add the below line to inject HttpClient dependency.

using AzureFuncDependencyDemo.Customer.Service;
using Microsoft.Azure.Functions.Extensions.DependencyInjection;
using Microsoft.Extensions.DependencyInjection;
[assembly: FunctionsStartup(typeof(AzureFuncDependencyDemo.Startup))]
namespace AzureFuncDependencyDemo
{
    public class Startup : FunctionsStartup
    {
        public override void Configure(IFunctionsHostBuilder builder)
        {
            builder.Services.AddHttpClient();
            builder.Services.AddTransient<ICustomerService, CustomerService>();
        }
    }
}

Now create another Azure function and use the HttpClient to fetch the user's data using the 'jsonplaceholder.typicode.com/users' mock api. Right-click on the solution and click on Add -> New Azure Function.

Select the Azure function give it the name "GetUsers" and click on the Add button.

Select function trigger type as HttpTrigger and Authorization level as Anonymous.

Now add the below code to fetch the user's data.

using System.Net.Http;
using System.Threading.Tasks;
using Microsoft.AspNetCore.Http;
using Microsoft.AspNetCore.Mvc;
using Microsoft.Azure.WebJobs;
using Microsoft.Azure.WebJobs.Extensions.Http;
using Microsoft.Extensions.Logging;
namespace AzureFuncDependencyDemo
{
    public class GetUsers
    {
        private readonly HttpClient _httpClient;
        public GetUsers(HttpClient httpClient)
        {
            _httpClient = httpClient;
        }
        [FunctionName("GetUsers")]
        public async Task<IActionResult> Run(
            [HttpTrigger(AuthorizationLevel.Anonymous, "get", Route = null)] HttpRequest req,
            ILogger log)
        {
            log.LogInformation("C# HTTP trigger function processed a request.");
            var responseMessage = await _httpClient.GetAsync("http://jsonplaceholder.typicode.com/users");
            var usersData = responseMessage.Content.ReadAsStringAsync().Result;
            return new OkObjectResult(usersData);
        }
    }
}

Here we have injected HttpClient dependency using Constructor and then called the GetAsync method to fetch data from api. So run the application and see the output.

Conclusion

In this article, we have created a new Azure function and a simple mock CustomerService from Visual Studio. Also, I demonstrated how to inject CustomerService dependency into the Azure function app and also inject it into the function. I hope that you enjoy this article, share it with friends, and please do not hesitate to send me your thoughts or comments.

Stay tuned for more Azure Functions articles.

You can follow me on Twitter @sumitkharche01 and Sumit Kharche

Happy Coding!