CODEWITHSUNDEEP
c#asp.net-coredependency-injection
Urgen
Urgen

Reputation: 1233

Dependency Injection ASP.NET Core Singleton

May I know what is wrong with following line of code:-

Why I can't use singleton on it?

services.AddSingleton<IProductRepository, ProductRepository>();

I have been getting 500 internal server error on the above code, however it is working fine with Transient and Scoped.

Upvotes: 2

Views: 5873

Answers (2)

TanvirArjel
TanvirArjel

Reputation: 32139

According to Microsoft Documentiaon:

It's dangerous to resolve a scoped service from a singleton. It may cause the service to have incorrect state when processing subsequent requests.

Now look at the following code of your ConfigureServices method in Startup class:

services.AddDbContext<ApplicationDbContext>(options =>
                       options.UseSqlServer(Configuration.GetConnectionString("DefaultConnection")));

There is a second parameter in the UseSqlServer method for Service Lifetime whose default value is ServiceLifetime.Scoped. May be you didn't specify the second parameter so it is taking the default value ServiceLifetime.Scoped. That means your DbContext has been registered as Scoped service. Now if you use your DbContext in ProductRepository then your ProductRepository has to be resisted as Scoped Service too otherwise ASP.NET Core DI provider cannot resolve it.

Now If you really want to register your ProductRepository as Singleton Service then make your DbContext also Singleton as follows:

services.AddDbContext<ApplicationDbContext>(options =>
                    options.UseSqlServer(Configuration.GetConnectionString("DefaultConnection")),ServiceLifetime.Singleton);

Now it should work!

Note: I assumed that your ProductRepository is dependent on DbContext. If not then your ProductRepository repository must be dependent on a service which is registered as a Scoped Service and that's why currently you are not able to use ProductRepository as Singleton.

Upvotes: 1

Nkosi
Nkosi

Reputation: 247571

I assume based on the provided pattern that the repository depends on a DbContext? 

public class ProductRepository : IProductRepository {

    public ProductRepository (MyDbContext db) {
        //...
    }
}

Which tends to be registered as scoped.

If you try to register a singleton with scoped dependencies, it may cause the service to have incorrect state when processing subsequent requests.

Reference Dependency injection in ASP.NET Core : Service Lifetimes

Upvotes: 3

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