Simple Injector - Injecting IDbContextScopeFactory

[wheeeels]

I'm trying to inject a IDbContextScopeFactory object using Simple Injector but I'm always getting the following error:

Additional information: The configuration is invalid. Creating the instance for type IDbContextScopeFactory failed. The constructor of type DbContextScopeFactory contains the parameter with name 'dbContextFactory' and type IDbContextFactory that is not registered. Please ensure IDbContextFactory is registered, or change the constructor of DbContextScopeFactory.

My problem is that I dont see an implementation of IDbContextFactory anywhere so I'm a little lost on how to resolve this situation. Any help is appreciated

[sliekens]

Apparently, providing an object that implements IDbContextFactory is completely optional.

public DbContextScopeFactory(IDbContextFactory dbContextFactory = null)
{
    _dbContextFactory = dbContextFactory;
}

But as you discovered, it seems that SimpleInjector does not support constructors with defaulted parameters (in this case the default is null).

I tried explicitly registering null for service type IDbContextFactory, but that is also not supported by SimpleInjector.

You could write your own implementation and register it in your container. The default implementation can be found here:
https://github.com/mehdime/DbContextScope/blob/master/Mehdime.Entity/Implementations/DbContextCollection.cs#L64-L68

public class DefaultDbContextFactory : IDbContextFactory
{
    public TDbContext CreateDbContext<TDbContext>() where TDbContext : DbContext
    {
        return Activator.CreateInstance<TDbContext>();
    }
}

container.Register<IDbContextFactory, DefaultDbContextFactory>();

@mehdime you could improve support for dependency injection by splitting the DbContextCollection constructor into overloads with and without parameters.

// default ctor for improved support for dependency injection containers that don't support default parameters
public DbContextScopeFactory()
    : this(null)
{
}

public DbContextScopeFactory(IDbContextFactory dbContextFactory = null)
{
    _dbContextFactory = dbContextFactory;
}

[wheeeels]

With that default implementation, I can now inject without any problems.
Thank you for your help!

[simon-nguyen]

@wheeeels, @StevenLiekens
I am using SimpleInjector too, and the library allows me to manage the lifetime of an instance (Scoped, Transient, Singleton) when registering in an Owin WebApi 2 application. In case of DbContextScope I am currently using as below

var container = new Container();

// To allow scoped instances to be resolved during an OWIN request,
// the following registration needs to be added to the IAppBuilder instance:
app.Use(async (context, next) =>
{
    using (container.BeginExecutionContextScope())
    {
          await next();
     }
});

/**
 * There will be only one instance of a given service type within a certain (explicitly defined) scope and
 * that instance will be disposed when the scope ends(unless specified otherwise).
 * This scope will automatically flow with the logical flow of control of asynchronous methods.
 **/
container.Options.DefaultScopedLifestyle = new ExecutionContextScopeLifestyle();

container.Register<IDbContextFactory, DefaultDbContextFactory>(Lifestyle.Scoped);
container.Register<IDbContextScopeFactory, DbContextScopeFactory>(Lifestyle.Scoped);
container.Register<IAmbientDbContextLocator, AmbientDbContextLocator>(Lifestyle.Scoped);

container.Register<IRepositoryAsync<User>, Repository<User>>(Lifestyle.Scoped);

container.Register<IUserService, UserService>(Lifestyle.Scoped);

container.Verify();

My question is "Does Lifestyle.Scoped suit for Owin WebApi 2 which is using DbContextScope?".

I've read that LifeStyle.Scoped will ensure the container its disposal if the type of cached instance implements IDisposable.

There's already a thread that said Singleton would make sense. But I see that you two have been using SimpleInjector so please give me some advise. Thank you.

[sliekens]

I don't know, sorry.

[rlightner]

@simon-nguyen What does your Repository class look like?