How to use DI in this example? - azure

Question

I followed this example https://learn.microsoft.com/pt-br/azure/app-service/webjobs-sdk-get-started and it is working fine. What I want to do is to make the connection strings (strongly typed) available in all methods within Functions class. My Connection Strings object:
namespace MyApp.Domain
{
public class Secrets
{
public class ConnectionStrings
{
public string SqlServer {get; set;}
public string Storage {get; set;}
public string SendGrid {get; set;}
public string AzureWebJobsDashboard { get; set; }
public string AzureWebJobsStorage {get; set;}
}
}
}
In web project I use (and it works perfectly):
services.Configure<Secrets.ConnectionStrings>(Configuration.GetSection("CUSTOMCONNSTR_ConnectionStrings"));
and in the classes' constructors I use:
public class EmailController: ControllerBase
{
private readonly MyEmail _myEmail;
public EmailController(MyEmail MyEmail)
{
_myEmail = MyEmail;
}
[HttpGet]
public async Task<ActionResult<string>> SendEmail()
{
try
{
...
return await _myEmail.SendMailMI3D(myMsg);
}
catch (System.Exception ex)
{
return ex.Message + " - " + ex.StackTrace;
}
}
[HttpGet("sendgrid")]
public string GetSendGrid(long id)
{
return _myEmail.SendGridConnStr();
}
}
But this way doesn't work on webjobs (console apps).
I tried to insert a simple Console.WriteLine in Functions' constructor but it doesn't work as well. So I think this is the problem: Functions' constructor is not being called. So when I insert a message in my queue I receive this error message related to DI Connection String:
Microsoft.Azure.WebJobs.Host.FunctionInvocationException: Exception while executing function: Functions.ProcessQueueMessage ---> System.NullReferenceException: Object reference not set to an instance of an object.
Can anybody please help me? Thanks a lot.
public Functions(IOptions<Secrets.ConnectionStrings> ConnectionStrings)
{
_connectionStrings = ConnectionStrings;
Console.WriteLine("Simple line");
Console.WriteLine($"Functions constructor: ${_connectionStrings.Value.SendGrid}");
}
Microsoft.Azure.WebJobs.Host.FunctionInvocationException: Exception while executing function: Functions.ProcessQueueMessage ---> System.NullReferenceException: Object reference not set to an instance of an object.

Answer 1

Dependency Injection is available in WebJobs but you do need to take the extra step to create an IJobActivator to define the injection.
namespace NetCoreWebJob.WebJob
{
public class JobActivator : IJobActivator
{
private readonly IServiceProvider services;
public JobActivator(IServiceProvider services)
{
this.services = services;
}
public T CreateInstance<T>()
{
return services.GetService<T>();
}
}
}
Inside Main()
var config = new JobHostConfiguration();
config.JobActivator = new JobActivator(services.BuildServiceProvider());
That should allow the runtime to utilize the parameterized constructor.