InstancePerRequest DbContext ASP.NET MVC

Question

Registering DbContext in ASP.NET MVC Application as InstancePerRequest . ( IoC Autofac )

builder.RegisterType<ADbContext>().As<IADbContext>().InstancePerRequest();

Using inside BService

public class BService : IBService
{
    readonly IADbContext _dbContext;
    public BService(IADbContext dbContext)
    {
        _dbContext = dbContext;
    }
}

Trying to register IBService as Singleton.

builder.RegisterType<BService>().As<IBService>().SingleInstance();

Obviously, this gives me an error

No scope with a tag matching 'AutofacWebRequest' is visible from the scope in which the instance was requested.

Simplest solution is to register IBService as InstancePerRequest , but there is no reason having PerRequest IBService rather than error message mentioned above.

How can i use PerRequest DbContext inside Singleton service ?

Answer 1

First attempt, you can inject IContainer into BService. But this will look like Service locator pattern, which is not good. Otherwise, you can define factory interface

public interface IFactory<T>
{
    T GetInstance();
}

Then implement it and register

public class SimpleFactory<T> : IFactory<T>
{
    private IContainer _container;

    public SimpleFactory(IContainer container)
    {
        _container = container;     
    }

    public T GetInstance()
    {
        return _container.Resolve<T>();
    }
}

public class DbContextFactory : SimpleFactory<IADbContext>
{   
    public DbContextFactory(IContainer container):base(container)
    {   
    }
}

Finally, use this factory in your singletone

public class BService : IBService
{
    IADbContext _dbContext =>  _dbContextFactory.GetInstance();
    IFactory<IADbContext> _dbContextFactory

    public BService(IFactory<IADbContext> dbContextFactory)
    {
        _dbContextFactory = dbContextFactory;
    }
}

Each time, when you want to acess to context inside singletone, it will pass this request to IoC container, which able to return context per request.