I am porting from traditional mvc to .net core
There is a static class where values are assigned on application start.
public static class WPSGlobalSettings
{
private static readonly string ToolboxDatabaseName = GetValue<string>("tbdatabasename", "db");
public static NpgsqlConnectionStringBuilder ToolboxConnString = build_conn_str(ToolboxDatabaseName);
...
}
However when I try to access it from Controller, it throws exception and is null
public class StatusController : Microsoft.AspNetCore.Mvc.ControllerBase
{
protected StatusDAL status_dal= new StatusDAL(WPSGlobalSettings.ToolboxConnString);
...
}
I want to understand why it stopped working after porting and how does Dependency Injection help here?
Note: I have resolved the issue here but want to clear my concepts.
Related
I have configured my .net-core 2.1 service with a database-context in the start-up method.
services.AddDbContext<DatabaseContext>(options => options.UseSqlServer(Configuration.GetConnectionString(nameof(DatabaseContext))));
Now i could do the following to get my database-context in my controller:
var context = serviceProvider.GetService<DatabaseContext>();
This works very well. But how could i access the Database-Context in a normal class something like this sould be done:
public class MyAccessClass{
public MyAccessClass(){
//Access the ServiceProvider or get the Database-Context class anywhere else
}
}
I don't want to pass the database-context object through the constructor or to initialize the DatbaseContext Class again.
Thanks for your help.
You should take your dependencies through the constructor, preferrably an interface, e.g. IDatabaseContext, but code sample below based on your code. If you add MyAccessClass as a service, e.g. services.AddTransient<MyAccessClass>(), and then use dependency injection in your controller, the database context would be automatically injected in the constructor by the default IoC container in ASP.NET Core.
You shouldn't have it rely on IServiceProvider, the reasoning is that your class wants to make no assumption of implementations, it just needs the database context. Having it rely on IServiceProvider would assume this context, and any possible future dependencies, comes from the IoC in ASP.NET Core which may not be the case (what if you just want to release this as a class library later on?). It would make the MyAccessClass class hard to test and use outside of a controller.
You say in your comment:
"...or get the Database-Context class anywhere else"
That anywhere else is completely flexible by simply accepting the context into the constructor since your class doesn't know where anywhere else is but whatever is creating your class does know!
Example of DI in ASP.NET Core
Take context as a dependency through constructor
public class MyAccessClass{
private readonly DatabaseContext databaseContext;
public MyAccessClass(DatabaseContext databaseContext) {
this.databaseContext = databaseContext;
}
}
Add as service
public void ConfigureServices(IServiceCollection services)
{
services.AddTransient<MyAccessClass>();
}
Inject into a controller
public class MyController : Controller
{
private readonly MyAccessClass myAccessClass;
//Happily injected through DI
public MyController(MyAccessClass myAccessClass)
{
this.myAccessClass = myAccessClass;
}
}
Or inject straight into an action
public class MyController : Controller
{
public MyController()
{
}
public IActionResult MyAction([FromServices] MyAccessClass myAccessClass)
{
}
}
I am using jaxrs 2.0 & am trying to populate an object in the ContainerRequestContext & retrive it in the business logic.
I am populating the object in the ContainerRequestContext like :
#Override
public void filter(ContainerRequestContext requestContext) throws IOException {
MyObject myObject = new MyObject();
requestContext.setProperty("myObject", myObject);
}
And I am trying to read it in the business logic like :
#GET
#Path("/custom")
public String data(#Context ContainerRequestContext crc) {
Object pco = crc.getProperty("myObject");
}
I am using this approach from the example shared in : How to inject an object into jersey request context?
However I am getting the ContainerRequestContext crc as null. Can someone tell me what I could be doing wrong ?
I have tested the exact code asked in the question which works as it is with following setup:
spring-boot-starter-parent: 2.3.4.RELEASE
spring-boot-starter: inherited from parent
spring-boot-starter-jersey: inherited from parent
which evaluates to Spring 5.2.9.RELEASE, Jersey 2.30.1
Arquillian with Jersey can work.
On my service layer I have injected an UnitOfWork and 2 repositories in the constructor. The Unit of Work and repository have an instance of a DbContext I want to share between the two of them. How can I do that with Ninject ? Which scope should be considered ?
I am not in a web application so I can't use InRequestScope.
I try to do something similar... and I am using DI however, I need my UoW to be Disposed and created like this.
using (IUnitOfWork uow = new UnitOfWorkFactory.Create())
{
_testARepository.Insert(a);
_testBRepository.Insert(b);
uow.SaveChanges();
}
EDIT: I just want to be sure i understand… after look at https://github.com/ninject/ninject.extensions.namedscope/wiki/InNamedScope i though about my current console application architecture which actually use Ninject.
Lets say :
Class A is a Service layer class
Class B is an unit of work which take into parameter an interface (IContextFactory)
Class C is a repository which take into parameter an interface (IContextFactory)
The idea here is to be able to do context operations on 2 or more repository and using the unit of work to apply the changes.
Class D is a context factory (Entity Framework) which provide an instance (keep in a container) of the context which is shared between Class B et C (.. and would be for other repositories aswell).
The context factory keep the instance in his container so i don’t want to reuse this instance all the name since the context need to be disposed at the end of the service operaiton.. it is the main purpose of the InNamedScope actually ?
The solution would be but i am not sure at all i am doing it right, the services instance gonna be transcient which mean they actually never disposed ? :
Bind<IScsContextFactory>()
.To<ScsContextFactory>()
.InNamedScope("ServiceScope")
.WithConstructorArgument(
"connectionString",
ConfigurationUtility.GetConnectionString());
Bind<IUnitOfWork>().To<ScsUnitOfWork>();
Bind<IAccountRepository>().To<AccountRepository>();
Bind<IBlockedIpRepository>().To<BlockedIpRepository>();
Bind<IAccountService>().To<AccountService>().DefinesNamedScope("ServiceScope");
Bind<IBlockedIpService>().To<BlockedIpService>().DefinesNamedScope("ServiceScope");
UPDATE: This approach works against NuGet current, but relies in an anomaly in the InCallscope implementation which has been fixed in the current Unstable NuGet packages. I'll be tweaking this answer in a few days to reflect the best approach after some mulling over. NB the high level way of structuring stuff will stay pretty much identical, just the exact details of the Bind<DbContext>() scoping will work. (Hint: CreateNamedScope in unstable would work or one could set up the Command Handler as DefinesNamedScope. Reason I dont just do that is that I want to have something that composes/plays well with InRequestScope)
I highly recommend reading the Ninject.Extensions.NamedScope integration tests (seriously, find them and read and re-read them)
The DbContext is a Unit Of Work so no further wrapping is necessary.
As you want to be able to have multiple 'requests' in flight and want to have a single Unit of Work shared between them, you need to:
Bind<DbContext>()
.ToMethod( ctx =>
new DbContext(
connectionStringName: ConfigurationUtility.GetConnectionString() ))
.InCallScope();
The InCallScope() means that:
for a given object graph composed for a single kernel.Get() Call (hence In Call Scope), everyone that requires an DbContext will get the same instance.
the IDisposable.Dispose() will be called when a Kernel.Release() happens for the root object (or a Kernel.Components.Get<ICache>().Clear() happens for the root if it is not .InCallScope())
There should be no reason to use InNamedScope() and DefinesNamedScope(); You don't have long-lived objects you're trying to exclude from the default pooling / parenting / grouping.
If you do the above, you should be able to:
var command = kernel.Get<ICommand>();
try {
command.Execute();
} finally {
kernel.Components.Get<ICache>().Clear( command ); // Dispose of DbContext happens here
}
The Command implementation looks like:
class Command : ICommand {
readonly IAccountRepository _ar;
readonly IBlockedIpRepository _br;
readonly DbContext _ctx;
public Command(IAccountRepository ar, IBlockedIpRepository br, DbContext ctx){
_ar = ar;
_br = br;
_ctx = ctx;
}
void ICommand.Execute(){
_ar.Insert(a);
_br.Insert(b);
_ctx.saveChanges();
}
}
Note that in general, I avoid having an implicit Unit of Work in this way, and instead surface it's creation and Disposal. This makes a Command look like this:
class Command : ICommand {
readonly IAccountService _as;
readonly IBlockedIpService _bs;
readonly Func<DbContext> _createContext;
public Command(IAccountService #as, IBlockedIpServices bs, Func<DbContext> createContext){
_as = #as;
_bs = bs;
_createContext = createContext;
}
void ICommand.Execute(){
using(var ctx = _createContext()) {
_ar.InsertA(ctx);
_br.InsertB(ctx);
ctx.saveChanges();
}
}
This involves no usage of .InCallScope() on the Bind<DbContext>() (but does require the presence of Ninject.Extensions.Factory's FactoryModule to synthesize the Func<DbContext> from a straightforward Bind<DbContext>().
As discussed in the other answer, InCallScope is not a good approach to solving this problem.
For now I'm dumping some code that works against the latest NuGet Unstable / Include PreRelease / Instal-Package -Pre editions of Ninject.Web.Common without a clear explanation. I will translate this to an article in the Ninject.Extensions.NamedScope wiki at some stagehave started to write a walkthrough of this technique in the Ninject.Extensions.NamedScope wiki's CreateNamedScope/GetScope article.
Possibly some bits will become Pull Request(s) at some stage too (Hat tip to #Remo Gloor who supplied me the outline code). The associated tests and learning tests are in this gist for now), pending packaging in a proper released format TBD.
The exec summary is you Load the Module below into your Kernel and use .InRequestScope() on everything you want created / Disposed per handler invocation and then feed requests through via IHandlerComposer.ComposeCallDispose.
If you use the following Module:
public class Module : NinjectModule
{
public override void Load()
{
Bind<IHandlerComposer>().To<NinjectRequestScopedHandlerComposer>();
// Wire it up so InRequestScope will work for Handler scopes
Bind<INinjectRequestHandlerScopeFactory>().To<NinjectRequestHandlerScopeFactory>();
NinjectRequestHandlerScopeFactory.NinjectHttpApplicationPlugin.RegisterIn( Kernel );
}
}
Which wires in a Factory[1] and NinjectHttpApplicationPlugin that exposes:
public interface INinjectRequestHandlerScopeFactory
{
NamedScope CreateRequestHandlerScope();
}
Then you can use this Composer to Run a Request InRequestScope():
public interface IHandlerComposer
{
void ComposeCallDispose( Type type, Action<object> callback );
}
Implemented as:
class NinjectRequestScopedHandlerComposer : IHandlerComposer
{
readonly INinjectRequestHandlerScopeFactory _requestHandlerScopeFactory;
public NinjectRequestScopedHandlerComposer( INinjectRequestHandlerScopeFactory requestHandlerScopeFactory )
{
_requestHandlerScopeFactory = requestHandlerScopeFactory;
}
void IHandlerComposer.ComposeCallDispose( Type handlerType, Action<object> callback )
{
using ( var resolutionRoot = _requestHandlerScopeFactory.CreateRequestHandlerScope() )
foreach ( object handler in resolutionRoot.GetAll( handlerType ) )
callback( handler );
}
}
The Ninject Infrastructure stuff:
class NinjectRequestHandlerScopeFactory : INinjectRequestHandlerScopeFactory
{
internal const string ScopeName = "Handler";
readonly IKernel _kernel;
public NinjectRequestHandlerScopeFactory( IKernel kernel )
{
_kernel = kernel;
}
NamedScope INinjectRequestHandlerScopeFactory.CreateRequestHandlerScope()
{
return _kernel.CreateNamedScope( ScopeName );
}
/// <summary>
/// When plugged in as a Ninject Kernel Component via <c>RegisterIn(IKernel)</c>, makes the Named Scope generated during IHandlerFactory.RunAndDispose available for use via the Ninject.Web.Common's <c>.InRequestScope()</c> Binding extension.
/// </summary>
public class NinjectHttpApplicationPlugin : NinjectComponent, INinjectHttpApplicationPlugin
{
readonly IKernel kernel;
public static void RegisterIn( IKernel kernel )
{
kernel.Components.Add<INinjectHttpApplicationPlugin, NinjectHttpApplicationPlugin>();
}
public NinjectHttpApplicationPlugin( IKernel kernel )
{
this.kernel = kernel;
}
object INinjectHttpApplicationPlugin.GetRequestScope( IContext context )
{
// TODO PR for TrgGetScope
try
{
return NamedScopeExtensionMethods.GetScope( context, ScopeName );
}
catch ( UnknownScopeException )
{
return null;
}
}
void INinjectHttpApplicationPlugin.Start()
{
}
void INinjectHttpApplicationPlugin.Stop()
{
}
}
}
Grabbed this from a sample:
protected override ObjectContext CreateDataSource()
{
NorthwindContext nw = new NorthwindContext();
// Configure DbContext before we provide it to the
// data services runtime.
nw.Configuration.ValidateOnSaveEnabled = false;
// Get the underlying ObjectContext for the DbContext.
var context = ((IObjectContextAdapter)nw).ObjectContext;
// Return the underlying context.
return context;
}
Modified it to use the DbContext class that I have in my project.
EDIT: Clarifying that I am casting from a DbContext class just as the sample does:
public class NorthwindContext : DbContext
{
// Use the constructor to target a specific named connection string
public NorthwindContext()
: base("name=NorthwindEntities")
{
// Disable proxy creation as this messes up the data service.
this.Configuration.ProxyCreationEnabled = false;
// Create Northwind if it doesn't already exist.
this.Database.CreateIfNotExists();
}
Running the code gives me an error on the line casting the DbContext:
Unable to cast object of type 'MyProject.MyDbContext' to type 'System.Data.Entity.Infrastructure.IObjectContextAdapter'.
Despite the fact that DbContext implements IObjectContextAdapter:
public class DbContext : IDisposable, IObjectContextAdapter
I've found several questions here on SO and other googled sources, but no solutions I have found work.
I'm using Entity Framework 4.2, attempted to update to the 4.3 beta and I'm not sure if that stuck.
Overall goal is to serve data in WCF as a DataService.
Update: Digging deeper I find that there is an ambiguity issue between what my DbContext was (From EntityFramework.dll ) and the type in the WCF project (from Microsoft.data.Entity.CTP)
Not sure how to get what I want from both here....
Just a reminder, the issue here was that an ambiguity between EntityFramework.dll and Microsoft.Data.Entity.CTP was causing the DataInitializer I had for my DbContext to lose functionality.
I solved this issue by replacing my Initializer here:
public class MyDataInitializer : RecreateDatabaseIfModelChanges<MyData>
{
public void Seed(MyData context)
To:
public class MyDataInitializer : IDatabaseInitializer<MyData>
{
public void InitializeDatabase(MyData context)
And I can now access my DataService.
Just one
I've started playing with Wicket and I've chosen Guice as dependency injection framework. Now I'm trying to learn how to write a unit test for a WebPage object.
I googled a bit and I've found this post but it mentioned AtUnit so I decided to give it a try.
My WebPage class looks like this
public class MyWebPage extends WebPage
{
#Inject MyService service;
public MyWebPage()
{
//here I build my components and use injected object.
service.get(id);
....
}
}
I created mock to replace any production MyServiceImpl with it and I guess that Guice in hand with AtUnit should inject it.
Now the problems are:
AtUnit expects that I mark target object with #Unit - that is all right as I can pass already created object to WicketTester
#Unit MyWebPage page = new MyWebPage();
wicketTester.startPage(page);
but usually I would call startPage with class name.
I think AtUnit expects as well that a target object is market with #Inject so AtUnit can create and manage it - but I get an org.apache.wicket.WicketRuntimeException: There is no application attached to current thread main. Can I instruct AtUnit to use application from wicketTester?
Because I don't use #Inject at MyWebPage (I think) all object that should be injected by Guice are null (in my example the service reference is null)
I really can't find anything about AtUnit inside Wicket environment. Am I doing something wrong, am I missing something?
I don't know AtUnit but I use wicket with guice and TestNG. I imagine that AtUnit should work the same way. The important point is the creation of the web application with the use of guice.
Here how I bind all this stuff together for my tests.
I have an abstract base class for all my tests:
public abstract class TesterWicket<T extends Component> {
#BeforeClass
public void buildMockedTester() {
System.out.println("TesterWww.buildMockedTester");
injector = Guice.createInjector(buildModules());
CoachWebApplicationFactory instance =
injector.getInstance(CoachWebApplicationFactory.class);
WebApplication application = instance.buildWebApplication();
tester = new WicketTester(application);
}
protected abstract List<Module> buildModules();
The initialization is done for every test class. The subclass defines the necessary modules for the test in the buildModules method.
In my IWebApplicationFactory I add the GuiceComponentInjector. That way, after all component instantiation, the fields annotated with #Inject are filled by Guice:
public class CoachWebApplicationFactory implements IWebApplicationFactory {
private static Logger LOG = LoggerFactory.getLogger(CoachWebApplicationFactory.class);
private final Injector injector;
#Inject
public CoachWebApplicationFactory(Injector injector) {
this.injector = injector;
}
public WebApplication createApplication(WicketFilter filter) {
WebApplication app = injector.getInstance(WebApplication.class);
Application.set(app);
app.addComponentInstantiationListener(new GuiceComponentInjector(app, injector));
return app;
}
}