In a nutshell I'm in the process of upgrading a .NETStandard 2.1 app to .NET 6. Plus upgrading the various libraries accordingly, in particular MassTransit v5 to v8, and AutoFac 4.9.4 to 6.4.0.
This is a multi-tenant application where one instance is shared by multiple tenants, and each tenant has their own database.
The upgrade has gone well apart from one snag. The application uses the, no longer available, AutofacReceivedEndpointExtensions to setup the Tenant details in the Consumer, and I am struggling to find a way to replicate the functionally it provides.
Below is the key bit of code.
config.ReceiveEndpoint(host, azureBusConfig.QueueName, endpoint =>
{
ConfigureConsumer<MyConsumer>(endpoint, componentContext);
});
private static void ConfigureConsumer<TConsumer>(IServiceBusReceiveEndpointConfigurator endpoint, IComponentContext componentContext, Action<IConsumerConfigurator<TConsumer>> configure = null)
where TConsumer : class, IConsumer
{
endpoint.Consumer(componentContext, configure, configureScope: (container, context) =>
{
var tenantName = context.Headers.Get<string>("tenant");
var userId = context.Headers.Get<int>("userId");
container.RegisterInstance(new NamedTenantInfoProvider(tenantName, userId)).As<ITenantInfoProvider>();
});
}
The endpoint.Consumer method as shown is no longer provided.
The ITenantInfoProvider interface is injected into various constructors in the application e.g., to setup the dbContext for a tenant to point to the correct database.
public interface ITenantInfoProvider
{
string GetTenantName();
int? GetUserId();
}
There are two implementations of the ITenantInfoProvider. The NamedTenantInfoProvider which is used to set the Tenant from the received message, above.
There is also a RequestTenantInfoProvider, that gets the Tenant from the HttpRequest. e.g. via api call.
The RequestTenantInfoProvider is registered as follows
builder.RegisterType<RequestTenantInfoProvider>()
.As<ITenantInfoProvider>()
.InstancePerLifetimeScope();
So, what should happen is that the RequestTenantInfoProvider is injected into the constructors by default, but when a message is being consumed the NamedTenantInfoProvider instance is injected instead.
I have tried to register the NamedTenantInfoProvider as per the RequestTenantInfoProvider. Then inject an IEnumerable into the constructors. And set the Tenant in the consumer.ConfigureConsumer on the Named instance. Then use which ever instance has a Tenant set in the code. However, the NamedTenantInfoProvider instance is set after it is required in the other constructors e.g., dbContext.
The only way I can get the application to fully work is to hardcode a Tenant name in the NamedTenentInfoProvider class.
I was hoping that someone has already refactored some similiar code to replace the endpoint.ConfigureConsumer call and can advise a solution.
It may be that I'm missing a bit of knowledge regarding how scoping works with the Microsoft Dependency Injection/MassTransit configuration. Note: I didn't write the original application, and this is my first dabble with Mass Transit as well.
MassTransit v8 (and onward) only support IServiceCollection, which is part of Microsoft.Extensions.DependencyInjection. Third-party containers are no longer directly supported.
There is a Scoped Filter sample that might help you understand how scopes work with MSDI. The token concept is similar to that used by developers injecting "tenant info" into consumers.
Related
In case of a Web API, each request is a distinct scope and dependencies registered as scoped will get resolved per request. So resolving dependencies per request per tenant is easy as the tenant information (like TenantId) can be passed in the HTTP Request headers like below:
services.TryAddScoped<ITenantContext>(x =>
{
var context = x.GetService<IHttpContextAccessor>().HttpContext;
var tenantId = context.Request.Headers["TenantId"].ToString();
var tenantContext = GetTenantContext(tenantId);
return tenantContext;
}
Other registrations first resolve TenantContext and use it to resolve other dependencies. For example, IDatabase will be registered as below. During resolution it will resolve and connect to specific tenant database.
services.TryAddScoped<IDatabase>(x =>
{
var tenantContext = x.GetService<ITenantContext>();
return new Database(tenantContext.DatabaseConnectionString);
}
This is all good in a Web API service because each request is a scope. I am facing challenges using dependency injection in a multi-tenant Console App. Suppose the app processes items from a
multi-tenant queue and each message can belong to a different tenant. While processing each message, it commits data to tenant specific database. So in this case the scope is each message in a queue and message contains the tenantId.
So when the app reads a message from queue, it needs to get TenantContext. Then resolve other dependencies based on this TenantContext.
One straightforward option I see how this dynamic resolution can be achieved is to create the dependent objects manually using the TenantContext but then I wouldn't be able to leverage dependency injection. All objects would get created manually and disposed after going out of scope after the message is processed.
var messgage = GetMessageFromQueue(queueName);
var tenantContext = GetTenantContext(message.TenantId);
var database = GetDatabaseObject(tenantContext);
// Do other processing now we got the database object connected to specific tenant DB
Is there an option in DI where I can pass in the TenantId dynamically so that TenantContext gets set for this scope and then all further resolution within this scope leverage this TenantContext?
Because the role of the tenancy goes beyond the implementation ("this uses X database") and is actually contextual to the action being performed ("this uses X database and must use this connection string based on the context being handled in the action"), there's some risk of assuming that ambient context is present in alternate implementations due to it not expressly being described in your interface in some way, which is where the DI issue is coming up here.
You might be able to:
Update your interfaces so that the tenancy information is an expected parameter of your methods. This ensures that regardless of future implementation, the presence of the tenant ID is explicit in their signature:
public interface ITenantDatabase {
public TResponse Get(string TenantId, int Id);
//... other methods ...
}
Add a factory wrapper around your existing interfaces to handle assigning the context at object creation and have that factory return the IDatabase instance. This is basically what you are proposing manually but with an abstraction around it that you could register and inject to keep the code that leverages it from being responsible for the logic:
public interface ITenantDatabaseFactory {
public IDatabase GetDatabaseForTenant(int TenantId);
}
// Add an implementation that manually generates and returns the scoped objects
I have created a web api that handles the creation of jwt token based on the encrypted user details that it receives in a post request.
In addition to this STS api should also handle the population of the caching layer (Redis or Hazelcast) with all the user data present in the database. Presently I have registered the caching service using dependency injection.This will happen only once when the api is first initialized.
services.AddSingleton<ICacheService, RedisCacheService>();
And in the TokenController added the service as a parameter to initialize the CachingService class and thereby initialize the caching layer.So that when the cacheService object is fist initialized it fetches all the user rows from the database and stores it as a key value pair inside Redis/Hazelcast database.
public TokenController(
ICryptographyService cryptographyService,
crudDBContext crudDBContext,
IConfiguration configuration,
ICacheService cacheService)
{
_cryptographyService = cryptographyService;
_context = crudDBContext;
_config = configuration;
_cacheService = cacheService;
}
But the Token Controller constructor is initialized only when an endpoint is called, so i had to create a separate default [HttpGet] endpoint to ensure that the constructor is called when the STS api is first initialized so as to ensure that the cacheService object gets created and the data gets loaded to the cache.
public ActionResult<string> Get()
{
return "STS";
}
Please let me know if there is a proper way of doing this without calling an endpoint, like be able to use dependency injection but at the same time call some code without the endpoint being called.I need to use dependency injection because i should be able to switch between Redis and Hazelcast by just changing the classname in the startup.cs file.
With respect to Hazelcast and dependency injection: First you would need to use the sources and not the Hazelcast NuGet version. Next the configuration depends on if you are in a Container Environment or a Hosted Environment. In both cases configuration keys will be gathered from the same sources and in the same order, and options will be registered in the service container, and available via dependency injection
I'd like to start a WPF app using .NET Core 3.1
Can Prism make use of .Net Core's built-in DI (IServiceCollection) or do I have to use something like Unity?
If Prism cannot use the built-in DI, can they exist side-by-side?
Can Prism make use of .Net Core's built-in DI
From what I've seen you can't really replace Prism's DryIot with the ASP.NET Core build-in one. Mainly DryIot is more feature-full than the ServiceCollection API. There is this opensource package I've found that has an IContainerExtension implementation using ServiceCollection, but per the developer's own words this is more of a proof of concept rather than sable solution.
If Prism cannot use the built-in DI, can they exist side-by-side?
Yes, they can. With a caveat - you cannot simply register a service in ServiceCollection and expect to be able to inject that service directly in your App, Modules and ViewModels. This will fail because those files are managed by the Prism framework and thus injection will only work for services you have registered using the IContainerRegistry interface.
Benefits
Why would you do it? As the build-in IoT container the ServiceCollection API is well-known, thus it will be simpler for .Net developers. Furthermore you can structure you non-WPF projects to register services using the default container thus allowing them to be completely decoupled from your Desktop project. This is very good for more complex architectures like Domain-Driven Design.
Let's consider the following project structure:
solution
-- Desktop // Prism WPF application, containing only views and models
-- Application // Class library, containing operational logic.
Let's say that as a part of the Application project you need an IUserService which holds information about the current user that has to be populated in-memory when the user authenticates in the Desktop app. A registration method would look like this:
public IServiceCollection AddServices(this IServiceCollection services)
{
services.AddSingleton<IUserService, UserService>()
}
So now we need to inject it inside the Desktop project. I suggest two methods:
Simple
Seemless
Simple
This approach requires very simple startup configuration. The caveat is that you will not be able to inject your services directly in the constructor, but through the IServiceProvider interface.
Reference Microsoft.Extensions.DependencyInjection
Call your service registration method in App:
protected override void RegisterTypes(IContainerRegistry container)
{
// Build service provider using the ServiceCollection API
var provider = new ServiceCollection()
.AddServices()
.BuildServiceProvider();
// Register IServiceProvider within DryIot and provide
// a factory method to retrieve the service instance
container.Register<IServiceProvider>(() => provider);
}
Inject IServiceProvider where you need IUserService. For this example I'll use a Prism Module:
public class Module : IModule
{
private readonly IUserService userService;
public Module(IServiceProvider serviceProvider)
{
this.userService = serviceProvider.GetService<IUserService>();
}
...
private void Authenticate()
{
this.userService.IsAuthenticated = true;
}
}
That's it, you can now use your ServiceCollection registered dependency wherever you can access the IServiceProvider through Prism injection. This is the approach I recommend, because we are simply wrapping the .Net container in Prism's.
Seemless
This is where it gets a bit more interesting. Full disclaimer - you might encounter problems using this approach. I have not yet tested this beyond the most basic use-case. The only advantage this method offers is that you will be able to directly inject services in the constructor, instead of having to go through the IServiceProvider.
In its essence this method is simply looping through the ServiceCollection and registering all services directly in the Prism container. If we take a look at the implementation of ServiceCollection - it is simply a list of ServiceDescriptors. Upon further inspection we observe that ServiceDescriptior contains a bunch of constructors. We'll ignore those and focus on the properties:
ServiceType - the type that will be used when injecting
ImplementationType - type of the implementation to be injected
ImplementationInstance - instance of the implementation type
ImplementationFactory - factory delegate that returns an instance of the implementation type
LifeTime - Singleton, Scoped or Transient type
Let's now inspect the IContainerRegistry interface. We'll see that there are a lot of overloads of Register that accept Types, object and delegates.
Using that knowledge we can now create an adapter from ServiceDescriptor to registration of IContainerRegistry. The below implementation will only focus on Transient services, but the difference between service lifetimes is simply which registry method we call - Register for a Transient and RegisterSingleton for well Singletons.
Create and Adapter class with static method that accepts IContainerRegistry and ServiceDescriptor arguments:
public static void Register(IContainerRegistry container, ServiceDescriptor service)
{
// In case an implementation instance is provided we simply need to register it
if (service.ImplementationInstance != null)
{
containter.Register(service.ServiceType, service.ImplementationInstance);
}
// In case a factory is provided we have a bit more work.
// We need to modify it in order for it to be usable by the DryIot container
else if (service.ImlementationFactory != null)
{
var factory = service.ImplementationFactory;
var dryIotFactory = dryIotProvider =>
{
var provider = dryIotProvider.Resolve<IServiceProvider>();
return factory(provider);
};
container.Register(service.ServiceType, dryIotFactory);
}
// If no implementation or factory is provided then we simply register the
// types and let the container create the implementation instance on its own.
else
{
container.Register(service.ServiceType, service.ImplementationType);
}
}
The most tricky part here is the factory. To better understand factories in service-registration know that sometimes you may need access to other services to provide the correct implementation instance. For example if IHttpClient is registered you need to provide the IAuthorizationSerice with HttpAuthorizationService implementation instead of DesktopAuthorizationService.
Essentially we wrap the original factory method with a DryIot-compatible factory (accepts instance of DryIot container) that can supply the original factory with IServiceProvider instance.
Reference Microsoft.Extensions.DependencyInjection
Call your service registration method in App:
protected override void RegisterTypes(IContainerRegistry container)
{
var services = new ServiceCollection().AddServices()
foreach (var service in services)
{
Adapter.Register(container, service);
}
}
Inject IUserService directly in the module constructor:
public class Module : IModule
{
private readonly IUserService userService;
public Module(IUserService userService)
{
this.userService = userService;
}
}
Final thoughts
Again, I recommend the simple approach. Simplicity means lower learning curve and less room for errors. The inconvenience is minor in comparison.
Another fair warning - this is not production ready code. Especially the seemless method. I have yet to "battle-test" this implementation, but it might point you in the right direction.
If anyone has feedback/opinions I would be glad to read about it :)
Can Prism make use of .Net Core's built-in DI
Short Answer, NO
Here is a comment by #brianlagunas (The creator of Prism)
As I mentioned, we can't use IServiceProvider as we are in netstandard 1.0. The ServiceProvider and IServiceCollection is in netstandard 2.0. Also, there are a number of features that Prism needs that are to limited in the IServiceCollection implementation. Such as named instances and registrations, as well as a mutable container.
here is a comment by #dansiegel
I have spent a lot of time discussing this issue, and ultimately we cannot directly rely on IServiceProvider and IServiceCollection for a variety of reasons that extend beyond whether or not they are available.
here is the another comment also by
#brianlagunas
do I have to use something like Unity?
The ServiceCollection is "something like Unity". And, yes, you can use it with prism:
Create an IContainerExtension implementation that redirects to ServiceCollection
Derive from PrismApplicationBase and return your container extension from CreateContainerExtension
I have a user aggregate which is created using CreateUser command which consists of aggregate identifier and username.
Along with that i have domain service that communicates with mongo db and checks if username exists, if not it puts it there.
eg registerUsername(username) -> true / false whether it registered it or not
My question is, would it be good idea to create command handler on top of the user aggregate that would handle the CreateUser command and whether it has username or not will dispatch proper commands/events? like so:
#Component
class UserCommandHandler(
#Autowired
private val repository: Repository<User>,
#Autowired
private val eventBus: EventBus,
#Autowired
private val service: UniqueUserService
) {
#CommandHandler
fun createUser(cmd: CreateUser) {
if (this.service.registerUsername(cmd.username)) {
this.repository.newInstance { User(cmd.id) }
.handle(GenericCommandMessage(cmd))
} else {
this.eventBus.publishEvent(UserCreateFailed(cmd.id, cmd.username))
}
}
}
This question is not necessarily related to the set uniqueness in ddd but more of a question where should i put dependency of domain services? I could probably create user registration saga and inject that service inside saga but i think saga should only rely on command dispatching and not have any if/else logic.
I think the place to put your domain service depends on the use case at hand.
I typically try to have domain service do virtual no outbound calls to other services or databases, at all.
The domain service you're now conceiving however does exactly that to, like you're point out, solve the uniqueness issue.
In this situation, you could likely come by with the suggested approach.
You could also think of introducing a MessageHandlerInterceptor (or even fancier, a HandlerEnhancerDefinition as described here), specifically triggering on the create command and performing the desired check.
If it would be domain service like I depicted mine just now (e.g. zero outbound calls from domain service), then you can safely wire it in your command handling functions to perform some action.
If you're in a Spring environment, simply having your domain service as a bean and providing it as a parameter to your message handling function is sufficient for Axon to resolve it for you (through the means of ParameterResolvers, as described here).
Hope this helps you out #PolishCivil!
I'm building a site that relies quite heavily on a third party API so I thought it would make sense to package up the API wrapper as a service, however I'm starting to find instances where it would be useful to have access to it outside of a controller such as in an entity repository.
Also related to that is it would be useful to be able to get access to config values outside of a controller (again such as in an entity repository).
Can anyone tell me if this is possible and if not is there a suggested approach to doing this kind of thing?
thanks for any help
The Symfony distribution relies heavily on dependency injection. This means that usually, dependencies are injected directly into your object via the constructor, the setters or via other means (like reflection over properties). Your API wrapper service is then a dependency for other objects of your application.
That being said, it would be rather difficult to inject this service in an entity repository's constructor because it already requires some other parameters and I think it would not be possible to inject them because of the way we request the repository for an entity.
What you could do is to create another service which will be responsible of doing the work you were about to do in the entity repository. This way, you will be able to inject the entity manager, which will be used to retrieve the entity repository, you custom service and also another service holding your configuration values (There are other ways to share configuration values).
In my use case, I use a Facebook helper service that wraps Facebook API calls. This service is then injected where I need it. My entity repository is only responsible of doing database calls so it receives only the arguments it needs and not the whole dependency. Thus, it will not receive the helper but rather only the arguments needed to do a request, for example, a Facebook user id. In my opinion, this is the way to do it since I think the entity repository should not have dependencies on such helper objects.
Here a small example using YAML as the configuration:
# app/config/config.yml
services:
yourapp.configuration_container:
class: Application/AcmeBundle/Common/ConfigurationContainer
# You could inject configurations here
yourapp.api_wrapper:
class: Application/AcmeBundle/Service/ApiWrapperService
# Inject other arguments if needed and update constructor in consequence
yourapp.data_access:
class: Application/AcmeBundle/Data/Access/DatabaseAccessService
arguments:
entityManager: "#doctrine.orm.entity_manager"
apiWrapperService: "#yourapp.api_wrapper"
configuration: "#yourapp.configuration_container"
# Application/AcmeBundle/Common/ConfigurationContainer.php
public ConfigurationContainer
{
public function __construct()
{
// Initialize your configuration values or inject them in the constructor
}
}
# Application/AcmeBundle/Service/ApiWrapperService.php
public ApiWrapperService
{
public function __construct()
{
// Do some stuff
}
}
# Application/AcmeBundle/Data/Access/DatabaseAccessService.php
public DatabaseAccessService
{
public function __construct(EntityManager $entityManager, ApiWrapperService $apiWrapperService, ConfigurationContainer $configuration)
{
...
}
}
The at sign (#) in the config.yml file means that Symfony should inject another service ,having the id defined after the at sign, and not a simple string. For the configuration values, as I said previously, there is other means to achieve the same goal like using parameters or a bundle extension. With a bundle extension, you could define the configuration values directly into the config.yml and your bundle would read them.
In conclusion, this should give you the general idea of injecting services. Here a small list of documentation on the subject. Alot of links use the XML service definition instead of the YAML definition but you should be able to understand them quite easily.
Symfony Official DI
Fabien Potencier's articles on DI
Richard Miller's articles on DI (Check in his blog for the other DI articles)
Take note that the configuration I'm giving is working for Beta1 of Symfony2. I didn't update yet to Beta2 so there could be some stuff not working as they are in the Beta2 version.
I hope this will help you defining a final solution to your problem. Don't hesitate to ask other questions if you want clarifications or anything else.
Regards,
Matt
I would wrap this kind of behavior in a Symfony service(like a manager).
i would not inject any parameters or logic into the entity repositories, as they should mainly be used to fetch data using object manager queries.
I would put the logic in the services and if the service , require a database access it will call the entity repository to fetch data.