I have been writing a WPF DESKTOP application using NHibernate, WPF, Prism and Unity Container but have a problem in terms of Session Management in Services / Repositories and how to do it cleanly through dependency injection using Unity.
Having read Building A Desktop To Do-Application With NHibernate I now have a Session Per ViewModel / Presenter.
However, if I have several services on my viewmodel I have to pass the Session into each and every service which seems cumbersome and not quite right as I want to perform all data access through a repository.
e.g
CustomerMaintenanceViewModel
{
service1.Session = SessionForThisPresenter;
service2.Session = SessionForThisPresenter;
service3.Session = SessionForThisPresenter;
service1.GetAllSomething();
service2.GetAllSomething();
service3.GetAllSomething();
}
Each service is essentially a facade over a repository and I would want each repository for this presenter to be involved in the same session without explicitly setting it.
Any advice on how to handle this would be most appreciated as I am sure there is a solution quite close but I am not sure how to do it.
I suggest you look into uNhAddIns.
It has a full WPF example using MVVM.
Related
I am constructing a web service that receives data and updates it periodically. When a user pings the service, it will send specific data back to the user. In order to receive this data, I have a persistent that is created on startup and regularly receives updates, but not at periodic intervals. I have already implemented it, but I would like to add DI and make it into a service. Can this type of problem be solved with a BackgroundService or is this not recommended? Is there anything better I should use? I originally wanted to just register my connection object as a singleton, but since singletons are not initialized on startup, that does not work so well for me.
I thought I would add an answer as so expand on my comment. From what you have described, creating a BackgroundService is likely the best solution for what you want to do.
ASP.NET Core provides an IHostedService interface that can be used to implement a background task or service, in your web app. They also provide a BackgroundService class that implements IHostedService and provides a base class for implementing long running background services. These background services are registered within the CreateWebHostBuilder method in Program.cs.
You can consume services from the dependency injection container but you will have to properly manage their scopes when using them. You can decide how to manage your BackgroundService classes in order to fit your needs. It does take an understanding of how to work with Task objects and executing, queueing, monitoring them etc. So I'd recommend giving the docs a thorough read, so you don't end up impacting performance or resource usage.
I also tend to use Autofac as my DI container rather than the built in Microsoft container, since Autofac provides more features for resolving services and managing scopes. So it's worth considering if you find yourself hitting a wall because of the built in container.
Here's the link to the docs section covering this in much more depth. I believe you can also create standalone service workers now, so that might be worth a look depending on use case.
https://learn.microsoft.com/en-us/aspnet/core/fundamentals/host/hosted-services?view=aspnetcore-3.1&tabs=visual-studio
Edit: Here's another link to a guide an example implementation for a microservice background service. It goes a little more in depth on some of the specifics.
https://learn.microsoft.com/en-us/dotnet/architecture/microservices/multi-container-microservice-net-applications/background-tasks-with-ihostedservice#implementing-ihostedservice-with-a-custom-hosted-service-class-deriving-from-the-backgroundservice-base-class
I have an ASP.NET Core 2.2 app using EF Core 2.2.
I have some background worker threads which I start in ConfigureServices(). These threads depend on the DbContext and on other services which I register in ConfigureServices().
I found that when I try to use Add-Migration, the EF tools cause these threads to run, which in turn throw exceptions in the Add-Migration output because the threads try to access a database object that does not yet exist.
It appears the migration is created successfully, however, it makes using the tooling difficult because it appears to fail (exceptions in output, process does not exit, etc).
Some options I see to avoid this:-
a) Somehow detect in ConfigureServices() that the database does/does not match the context (i.e. is "up to date") and act accordingly.
b) Start my worker threads somewhere else that will not get invoked when my app is run by the EF tools. Keeping in mind that starting these threads require a ServiceProvider with the same scope I'm building in ConfigureServices().
c) Detect in my app that I'm being called by the EF tools and avoid launching the worker threads.
I'd appreciate any advice on the most appropriate strategy and the best method of achieving it.
EF Core tools use different strategies for creating derived DbContext, explained in the Design-time DbContext Creation section of the documentation.
Looks like currently you are using From application services. But according to the problem explanation, the most appropriate in your case seems to be From a design-time factory:
You can also tell the tools how to create your DbContext by implementing the IDesignTimeDbContextFactory<TContext> interface: If a class implementing this interface is found in either the same project as the derived DbContext or in the application's startup project, the tools bypass the other ways of creating the DbContext and use the design-time factory instead.
I'm creating a new application in Zend Framework 3 and i have a question about a design pattern
Without entering in much details this application will have several Services, as in, will be connecting to external APIs and even in multiple databases, the workflow is also very complex, a single will action can have multiple flows depending on several external information (wich user logged in, configs, etc).
I know about dependency injections and Zend Framework 3 Service Manager, however i am worried about instanciating sereval services when the flow will actually use only a few of them in certain cases, also we will have services depending on other services aswell, for this, i was thinking about using singletons.
Is singleton really a solution here? I was looking a way to user singletons in Zend Framework 3 and haven't figured out a easy way since i can't find a way to user the Service Manager inside a service, as I can't retrive the instance of the Service Manager outside of the Factory system.
What is an easy way to implement singletons in Zend Framework 3?
Why use singletons?
You don't need to worry about too many services in your service manager since they are started only when you get them from the service manager.
Also don't use the service manager inside another class except a factory. In ZF3 it's removed from the controllers for a reason. One of them is testability. If all services are inject with a factory, you can easily write tests. Also if you read your code next year, you can easily see what dependencies are needed inside a class.
If you find there are too many services being injected inside a class which are not always needed you can:
Use the ProxyManager. This lazy loads a service but doesn't start it until a method is called.
Split the service: Move some parts from a service into a new service. e.g. You don't need to place everything in an UserService. You can also have an UserRegisterService, UserEmailService, UserAuthService and UserNotificationsService.
In stead of ZF3, you can also think about zend-expressive. Without getting into too much detail, it is a lightweight middleware framework. You can use middleware to detect what is needed for a request and route to the required action to process the request. Something like this can probably also done in ZF3 but maybe someone else can explain how to do it there.
I'm currently working on an MVC4 project, i make use if Ninject to inject a UnitOfWork into my controllers, and I'm using UnitOfWork + Generic Repository pattern.
I don't like VS2012 MVC4 template because it directly uses database access (db initialization, for example).
My project divides in:
a UI project (the mvc4 application), with Forms Authentication
a Domain project (the db entities, the repositories, the UnitOfWork interface plus two UnifOfWork implementations, one with MOQ and one with EF; they are injected into UI controllers via Ninject).
I looked at this example:
http://kevin-junghans.blogspot.it/2013/03/decoupling-simplemembership-from-your.html
related to this question
SimpleMembership - anyone made it n-tier friendly?
And now I have some question:
How can i inject my UoW here? WebSecurity class is static, there is no contructor, it directly instantiate the UoW to perform activities on db ...
I always have to initialize WebMatrix to directly access DB? This piece of code:
public static void Register()
{
Database.SetInitializer<SecurityContext>(new InitSecurityDb());
SecurityContext context = new SecurityContext();
context.Database.Initialize(true);
if (!WebMatrix.WebData.WebSecurity.Initialized)
WebMatrix.WebData.WebSecurity.InitializeDatabaseConnection("DefaultConnection",
"UserProfile", "UserId", "UserName", autoCreateTables: true);
}
breaks my decoupling with the Domain .. how can i make WebSecurity using my UnitOfWork for example? what is the best practice?
How can i store additional data (for example, EmailAddress and so on) and retrieve it, without performing a Database query everytime i have to access the User profile? Something like the old CustomPrincipal ... Custom principal in ASP.NET MVC
Thank you!
You have a lot of questions here Marco. Let me take a stab at them.
How to inject a UOW
Static classes and dependency injection do not mix well, as pointed out in this QA. When I first went through this exercise of decoupling SimpleMembership the concentration was just on decoupling from the domain, as discussed in the article you referenced. It was just a first step and it can be improved on, including making it easier for dependency injection. I debated whether to make WebSecurity static or not and went with static because that is how the original SimpleMembership is implemented, making it a more seamless transition for user of the SimpleSecurity. SimpleSecurity is an open source project and contributions are welcome. Making it non-static would not be difficult and probably makes sense in the long run. Once it is made non-static we could use a Factory pattern to create the UnitOfWork and inject the appropriate Factory.
Why do I have to Register WebSecurity?
SimpleSecurity is just a wrapper around the WebMatrix WebSecurity classes, which require initialization. The Register method just makes sure that WebMatrix is initialized and initializes our database. I disagree that having this method call in the Globa.asax couples it with the Domain in any way. Having it work with your UnitOfWork should have nothing to do with the Application Domain, or with having to call a Register method at application start-up.
How can I store additional data (ex: email) and retrieve it, without performing a database query every time?
This is actually accomplished quite easy in .NET 4.5 by using ClaimsPrincipal. All principals in .NET 4.5 inherit from ClaimsPrincipal, which allows you to store information in the principal as claims. Claims are basically key value pairs that let you store any type of data on the user. For example in ASP.NET the roles for a user are stored as claims. To add your own claims you need to do something called claims transformation. Then to retrieve the information you can create a custom claims principal. Adding this to SimpleSecurity would be a nice feature.
Clarified Updated Question - Start
In the official MVC 3 Getting Started-tutorial it seems to me that all we have to do to get ORM working are two steps.
First adding the simple MovieDBContext-code as described at the end of part 4 ..
public class MovieDBContext : DbContext
{
public DbSet<Movie> Movies { get; set; }
}
.. and second in the beginning of part 5, with a simple right-click on the Controllers folder we can auto-generate a MoviesController that implements CRUD()-functionality using Entity Framework by simply telling which Model to use.
Now when using the web-application we can already write and read from the database.
What would be the simplest (or a simple) way to get this done for our Movie-Model with NHibernate instead of using Entity Framework?
Clarified Updated Question - End
Original question (only for additional background-info):
I'm trying to create an ASP.Net MVC 3 application that uses NHibernate and Postgres.
Background Info
Development is done on Windows with Visual Web Developer Express, the production environment will be/should be Linux+Mono.
Steps that have worked so far:
An ASP.Net Dynamic Data Entities Web Application using Npgsql and Postgres as the DB.
Successfully run on Windows development machine.
(Following this tutorial)
An ASP.Net MVC 3 application without using a database/model yet:
Succesfully run on Windows development machine and deployed to Linux production environment using Mono and Nginx. (Only as a proof of concept for myself not as a web app used by the public.)
An ASP.Net MVC 3 application with a model using SQL Server Express as the DB.
Successfully run on my Windows development machine.
(Following the MVC 3 Getting Started-tutorial)
Question
So far I managed to get Postgres to work with a "Dynamic Data Entities Web Application" but with an MVC 3 Web app I'm stuck on where/how to start. For the last mentioned MVC-3-Movie-Webapp I want to switch the DB from SQL Server Express to Postgres using NHibernate and Npgsql (NHibernate since Mono doesn't support Entity Framework).
When you look at the end of part 4 there's the simple MovieDBContext-code
public class MovieDBContext : DbContext
{
public DbSet<Movie> Movies { get; set; }
}
and in the beginning of part 5, we autogenerate CRUD-stuff using Entity Framework by simply telling which Model to use.
(MoviesController.cs, Create.cshtml, Delete.cshtml, Details.cshtml, Edit.cshtml, and Index.cshtml)
So I have that working with Entity Framework and SQL Server Express, but how would I achieve the same result by using NHibernate? (doesn't have to be with postgres immediately, sticking with SQL-Server as a first step would be fine) (Hopefully with similar simplicity, but getting the result itself would be great)
I found a lot of old stuff and how I would manually map things, but what would be a good-up to date standard way of achieving this with NHibernate for MVC 3?
(The closest thing I found was the source code mentioned in this thread, but it's 64 MB unzipped I got several "Projects not loaded successfully"-errors and the author said he uses MVC 2 so I think it's a little over my head for being a complete NHibernate noob.)
I think showing how this is done could be very useful for others as well, since the original tutorial is very easy to follow and is linked as the official starting point for MVC 3 app-development on http://www.asp.net/mvc ("Your First ASP.NET MVC App").
So I think this would be a great up to date example about how to use NHibernate with MVC 3.
Actually, those automated things haven't helpful enough in real world applications. We have to separate concerns and by using DataContext in UI Layer is not a good practice because that dependency will cause problems like lack of test-ability, violation of best practices. I think you need to have following things of your project
Separation of Concern (Layered Architecture - UI Layer, Servie Layer, Domain Layer, Infrastructure Layer)
Generic Repository and Unit of Work wrapping (Database functionalities, ORM - EF, NHibernate, etc
In your Service Layer process repositories and unit of work processings and expose Data Transfer objects or your domain objects (POCOs) to UI Layer
Use IOC to inject dependencies will help you to minimize dependencies
Create Unit test and Integration tests
Use Continuous Integration and Source control prefer (Distributed: Mercurial)
Useful References:
(Sharp Architecture) http://sharparchitecture.codeplex.com/
(IOC Container) http://www.castleproject.org/container/
(Generic repository) http://code.google.com/p/genericrepository/
NuGet is your friend. Here's a good example of using NuGet to automatically wire in your dependencies and configuration pretty much automatically.
Hope this helps.
Suggestion, don't get hung up on all the automatic stuff that the tutorials are showing you. Microsoft is just trying to show that you can easily get things started if you don't try to do anything unique.
Now for your situation. When you're making a controller, you're wanting to bind that controller with a type of model that you created somewhere. With nHibernate I'm thinking that you'll have manually created these POCO's and that you're using one of the many ways to map those POCO's through nHibernate to your database.
You won't be able to use the Entity Framework options because they're depending upon the features of the framework to provide information on the object, database, etc. Easiest things is to just make a controller that either gives you the options for CRUD or use an empty controller to build up your own ActionResults.
Hope this helps some and good luck with your project.