How to Use EF Dependency Injection with Called Method

Question

Hello everyone and thanks for the help in advance. Attempting to learn dependency injection concepts with C# and MVC controller. I am reading through the article https://learn.microsoft.com/en-us/ef/core/dbcontext-configuration/. My question is, let's assume within my MVC controller, an async method is called requiring the context object. Should you instantiate the context in the controller, then pass it to the method that consumes it, or do I instantiate it within the method. My controller may need to make more than one method call where each method requires the context. How should this be handled?

Answer

Hi @Kmcnet Thanks for sharing your concern with us. Regarding your question tough our official document clear instruction for your scenario however, I am trying to explain it as per your scenario.

In genral ApplicationDbContext can be used in ASP.NET Core controllers or other services through constructor injection Like below:

public class HomeController  
{  
    private readonly ApplicationDbContext _context;  
  
    public HomeController(ApplicationDbContext context)  
    {  
        _context = context;  
    }  
}

Note: Once you initiate the _context globally then it can be used in Controller Action level. Now let's consider your below scenario:

Question: My controller may need to make more than one method call where each method requires the context. How should this be handled?

As you might know Entity Framework Core does not support multiple parallel operations being run on the same DbContext instance. In that case, if you only need to call the method one after another then async, await can resolve your issue. However, if you want to call them concurrently then this way won't work for you and it will throw InvalidOperationException

Handle Parallel Method Operation:

Using dependency injection, this can be achieved by either registering the context as scoped, and creating scopes (using IServiceScopeFactory) for each thread, or by registering the DbContext. For example

public class EFDenpendencyHostedService : IHostedService  
{  
    private readonly IServiceScopeFactory scopeFactory;  
  
    public EFDenpendencyHostedService(IServiceScopeFactory scopeFactory)  
    {  
        this.scopeFactory = scopeFactory;  
    }  
  
    public void ExecuteDbContext()  
    {  
        using (var scope = scopeFactory.CreateScope())  
        {  
            var dbContext = scope.ServiceProvider.GetRequiredService();  
            …  
        }  
    }  
    …  
}

Note: Once you have created the middleware hosted service then register it in the startup.cs/ program.cs class

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Md Farid Uddin Kiron

How to Use EF Dependency Injection with Called Method

1 answer