In other DI containers, I have observed TryAddScoped, TryAddTransient, TryAddSingleton etc.
The idea behind Try is to avoid registering multiple times. If a service is already registered, then using Try will not attempt to register again I guess.
With inject
Kernel.Bind<IHttpContextAccessor>().To<HttpContextAccessor>().InSingletonScope();
So is there any Try equivalent in Ninject?
There's no simple equivalent.
Performing
Kernel.Bind<IHttpContextAccessor>().To<HttpContextAccessor>().InSingletonScope();
Kernel.Bind<IHttpContextAccessor>().To<HttpContextAccessor>().InSingletonScope();
will result in in an exception when resolving a IHttpContextAccessor, and when resolving IEnumerable<IHttpContextAccessor> it will return two HttpContextAccessor instances.
However, you can write your own "Try":
Checking whether Binding already exists
if(!Kernel.GetBindings(typeof(IHttpContextAccessor)).Any())
{
Kernel.Bind<IHttpContextAccessor>().To<HttpContextAccessor>().InSingletonScope();
}
Of course you can also write your own extension method for that:
public static class NinjectBindingExtensions
{
public static void TryBind<T>(
this IKernel kernel,
Action<IBindingToSyntax<T>> configureBinding)
{
if (!kernel.GetBindings(typeof(T)).Any())
{
configureBinding(kernel.Bind<T>());
}
}
}
Rebind
One way to work around the issue is to use .Rebind instead of .Bind. If there's no pre-existing binding it will work just like .Bind. And if there's a pre-existing binding, it will replace it. Thus:
Kernel.Rebind<IHttpContextAccessor>().To<HttpContextAccessor>().InSingletonScope();
Kernel.Rebind<IHttpContextAccessor>().To<HttpContextAccessor>().InSingletonScope();
Resolving IHttpContextAccessor will result in one instance of HttpContextAccessor.
Preventing Duplicate Module Loading
In case the problem is not with multiple components / NinjectModules creating bindings for the same type, but rather with loading the same NinjectModule twice, you can can prevent duplicate loading by:
if(!Kernel.HasModule(typeof(MyModule)))
{
Kernel.Load<MyModule>();
}
Related
I am looking for a way to dynamically select the correct dependency during runtime using google guice.
My usecase is a kotlin application which can work with either sqlite or h2 databases depending on the configuration file provided.
The file is read when the application is executed and if the database is not found, the correct one is created and migrated into.
My database structure contains the Database (Interface), H2Database: Database, SQLiteDatabase: Database and the module binding class which looks like this:
class DatabaseModule: KotlinModule() {
override fun configure() {
bind<Database>().annotatedWith<configuration.H2>().to<H2Database>()
bind<Database>().annotatedWith<configuration.SQLite>().to<SQLiteDatabase>()
}
}
So far, with SQlite alone, I would simply request the dependency using:
#Inject
#SQLite
private lateinit var database: Database
How would I make this selection during runtime?
Without knowing too much about the specific of your code, I'll offer three general approaches.
(Also, I have never used Kotlin. I hope Java samples are enough for you to figure things out.)
First Approach
It sounds like you need some non-trivial logic to determine which Database implementation is the right one to use. This is a classic case for a ProviderBinding. Instead binding Database to a specific implementation, you bind Database to a class that is responsible providing instances (a Provider). For example, you might have this class:
public class MyDatabaseProvider.class implements Provider<Database> {
#Inject
public MyDatabaseProvider.class(Provider<SQLiteDatabase> sqliteProvider, Provider<H2Database> h2Provider) {
this.sqliteProvider = sqliteProvider;
this.h2Provider = h2Provider;
}
public Database get() {
// Logic to determine database type goes here
if (isUsingSqlite) {
return sqliteProvider.get();
} else if (isUsingH2) {
return h2Provider.get();
} else {
throw new ProvisionException("Could not determine correct database implementation.");
}
}
}
(Side note: This sample code gets you a new instance every time. It is fairly straightforward to make this also return a singleton instance.)
Then, to use it, you have two options. In your module, you would bind Database not to a specific implementation, but to your DatabaseProvider. Like this:
protected void configure() {
bind(Database.class).toProvider(MyDatabaseProvider.class);
}
The advantage of this approach is that you don't need to know the correct database implementation until Guice tries to construct an object that requires Database as one of its constructor args.
Second Approach
You could create a DatabaseRoutingProxy class which implements Database and then delegates to the correct database implementation. (I've used this pattern professionally. I don't think there's an "official" name for this design pattern, but you can find a discussion here.) This approach is based on lazy loading with Provider using the Providers that Guice automatically creates(1) for every bound type.
public class DatabaseRoutingProxy implements Database {
private Provider<SqliteDatabse> sqliteDatabaseProvider;
private Provider<H2Database> h2DatabaseProvider;
#Inject
public DatabaseRoutingProxy(Provider<SqliteDatabse> sqliteDatabaseProvider, Provider<H2Database> h2DatabaseProvider) {
this.sqliteDatabaseProvider = sqliteDatabaseProvider;
this.h2DatabaseProvider = h2DatabaseProvider;
}
// Not an overriden method
private Database getDatabase() {
boolean isSqlite = // ... decision logic, or maintain a decision state somewhere
// If these providers don't return singletons, then you should probably write some code
// to call the provider once and save the result for future use.
if (isSqlite) {
return sqliteDatabaseProvider.get();
} else {
return h2DatabaseProvider.get();
}
}
#Override
public QueryResult queryDatabase(QueryInput queryInput) {
return getDatabase().queryDatabase(queryInput);
}
// Implement rest of methods here, delegating as above
}
And in your Guice module:
protected void configure() {
bind(Database.class).to(DatabaseRoutingProxy.class);
// Bind these just so that Guice knows about them. (This might not actually be necessary.)
bind(SqliteDatabase.class);
bind(H2Database.class);
}
The advantage of this approach is that you don't need to be able to know which database implementation to use until you actually make a database call.
Both of these approaches have been assuming that you cannot instantiate an instance of H2Database or SqliteDatabase unless the backing database file actually exists. If it's possible to instantiate the object without the backing database file, then your code becomes much simpler. (Just have a router/proxy/delegator/whatever that takes the actual Database instances as the constructor args.)
Third Approach
This approach is completely different then the last two. It seems to me like your code is actually dealing with two questions:
Does a database actually exist? (If not, then make one.)
Which database exists? (And get the correct class to interact with it.)
If you can solve question 1 before even creating the guice injector that needs to know the answer to question 2, then you don't need to do anything complicated. You can just have a database module like this:
public class MyDatabaseModule extends AbstractModule {
public enum DatabaseType {
SQLITE,
H2
}
private DatabaseType databaseType;
public MyDatabaseModule(DatabaseType databaseType) {
this.databaseType = databaseType;
}
protected void configure() {
if (SQLITE.equals(databaseType)) {
bind(Database.class).to(SqliteDatabase.class);
} else if (H2.equals(databaseType)) {
bind(Database.class).to(H2Database.class);
}
}
}
Since you've separated out questions 1 & 2, when you create the injector that will use the MyDatabaseModule, you can pass in the appropriate value for the constructor argument.
Notes
The Injector documentation states that there will exist a Provider<T> for every binding T. I have successfully created bindings without creating the corresponding provider, therefore Guice must be automatically creating a Provider for configured bindings. (Edit: I found more documentation that states this more clearly.)
For some reason this:
[Transaction]
public void DoSomething()
{
...
}
does not work I still have to explicitly use the transaction like this:
public void DoSomething()
{
using (var tx = NHibernateSession.Current.BeginTransaction())
{
....
tx.Commit();
}
}
Any ideas why?
I am using something like this to bootstrap stuff:
_container = new WindsorContainer();
ComponentRegistrar.AddComponentsTo(_container);
...
ServiceLocator.SetLocatorProvider(() => new WindsorServiceLocator(_container));
ComponentRegistrar.AddComponentsTo(_container, typeof(NHibernateTransactionManager));
NHibernateSession.Init(new ThreadSessionStorage(),
new[] { "Bla.Domain.dll" },
new AutoPersistenceModelGenerator().Generate(),
"NHibernate.config");
As Doan said the component that had the method is not proxied.
Since the method is not virtual, I am assuming that your class is implementing an interface. make sure that you have the dependency in the class calling DoSomething defined as the interface and not the implementing class.
if you debug the code, and check the run time type of the object, it should be a castle proxy
for more details check the trouble shooting section on Sharp Architecture contrib wiki
https://github.com/sharparchitecture/Sharp-Architecture-Contrib/wiki/Troubleshooting
Normally, this kind of problem is caused by the failure of invoking the dynamic proxy that provides the transaction management service. Two of the most common errors are:
The method cannot be proxied: most likely not implement any interface method, or the object was not proxied.
The method was called from the same class, which bypassed all proxies.
Edit:
I guess you use Castle Windsor as IoC container. The [Transaction] decoration requires the Automatic Transaction Management Facility in order to work. If you successfully configured the facility, i.e. you made [Transaction] work in one method, but not other, then the answer above applies. If all Transaction decoration failed to work, then you have to review the configuration of the facility first.
I have a service that takes a dependency on HttpContextBase.
Ninject is injecting this for me already as it's set up in the MvcModule to return new HttpContextWrapper(HttpContext.Current) when HttpContextBase is requested
I want to use this service in Application_AuthenticateRequest, so i'm using property injection so that Ninject resolves it for me
When I try and access Request.UserHostAddress on the HttpContextBase I get a Value does not fall within the expected range exception
If I call HttpContext.Current.Request.UserHostAddress directly it works without problems
ExampleService.cs
public class ExampleService : IExampleService {
HttpContextBase _contextBase;
public ExampleService(HttpContextBase contextBase) {
_contextBase = contextBase;
}
public void DoSomething() {
var ip = HttpContext.Current.Request.UserHostAddress; <== this works
ip = _contextBase.Request.UserHostAddress; <== this fails
}
}
Global.asax
[Inject]
public IExampleService ExampleService { get; set; }
public void Application_AuthenticateRequest() {
ExampleService.DoSomething();
}
I'm missing something here, but I can't see what
Dependencies that are injected into classes live as long as the the class they get injected into, because the class holds a reference to them. This means that in general you should prevent injecting dependencies that are configured with a lifetime that is shorter than the containing class, since otherwise their lifetime is 'promoted' which can cause all sorts of (often hard to track) bugs.
In the case of an ASP.NET application, there is always just one HttpApplication instance that lives as long as the AppDomain lives. So what happens here is that the injected ExampleService gets promoted to one-per-appdomain (or singleton) and since the ExampleService sticks around, so does its dependency, the HttpContextBase.
The problem here of course is that an HTTP context -per definition- can't outlive a HTTP request. So you're storing a single HttpContextBase once, but it gets reused for all other requests. Fortunately ASP.NET throws an exception, otherwise you would probably be in much more trouble. Unfortunately the exception isn't very expressive. They could have done better in this case.
The solution is to not inject dependencies in your HttpApplication / MvcApplication. Ever! Although it's fine to do so when you're injecting singletons that only depend on singletons recursively, it is easy to do this wrong, and there's no verification mechanism in Ninject that signals you about this error.
Instead, always resolve IExampleService on each call to AuthenticateRequest. This ensures that you get an ExampleService with the right lifetime (hopefully configured as per-web-request or shorter) and prevents this kind of error. You can either call into the DependencyResolver class to fetch an IExampleService or call directly into the Ninject Kernel. Calling into the Kernel is fine, since the Application_AuthenticateRequest can be considered part of the Composition Root:
public void Application_AuthenticateRequest() {
var service = DependencyResolver.Current.GetService<IExampleService>();
service.DoSomething();
}
I'm doing things considered horrible by some lately, but I personally enjoy this kind of experiment. Here's a telegraph style description:
Use NH to fetch data objects
Each DataObject is wrapped by a CastleDynamicProxy
When Properties decorated with Custom Attributes are queried, redirect to own code instead of NHibernate to get Returnvalue.
Object creation / data fetch code
Objects=GetAll().Select(x=>ProxyFactory.CreateProxy<T>(x)).ToList();
public IList<Person> GetAll()
{
ISession session = SessionService.GetSession();
IList<Person> personen = session.CreateCriteria(typeof(Person))
.List<Person>();
return personen;
}
The Proxy generation Code:
public T CreateProxy<T>(T inputObject)
{
T proxy = (T)_proxyGenerator.CreateClassProxy(typeof(T), new ObjectRelationInterceptor<T>(inputObject));
return proxy;
}
The Interceptor used is defined like so:
public class MyInterceptor<T> : IInterceptor
{
private readonly T _wrappedObject;
public MyInterceptor(T wrappedObject)
{
_wrappedObject = wrappedObject;
}
public void Intercept(IInvocation invocation)
{
if (ShouldIntercept(invocation)) { /* Fetch Data from other source*/ }
else
{
invocation.ReturnValue = invocation.Method.Invoke(_wrappedObject, invocation.Arguments);
}
}
public bool ShouldIntercept(IInvocation invocation)
{
// true if Getter / Setter and Property
// has a certain custom attribute
}
}
This works fine in an environment without NHibernate (creating objects in code, where the Object holds its own data).
Unfortunately, the else part in the Intercept method seems to leave NHibernate unfunctional, it seems the _wrappedObject is reduced to it's base type functionality (instead of being proxied by NHibernate), so all mapped Child collections remain empty.
I tried switching from lazy to eager loading (and confirmed that all SQL gets executed), but that doesn't change anything at all.
Does anybody have an idea what I could do to get this back to work?
Thanks a lot in advance!
I found out that what I do is partially wrong and partially incomplete. Instead of deleting this question, I chose to answer it myself, so that others can benefit from it as well.
First of all, I have misunderstood the class proxy to be an instance proxy, which is why i stored the _wrappedObject. I needed the Object to perform invocation.Method.Invoke(_wrappedObject, invocation.Arguments), which is the next mistake. Instead of doing so, I should have passed the call on to the next interceptor by making use of invocation.Proceed().
Now, where was that Incomplete? NH seems to need to know Metadata about it's instances, so I missed one important line to make NH aware that the proxy is one of its kin:
SessionFactory.GetClassMetadata(entityName).SetIdentifier(instance, id, entityMode);
This only works in an NHibernate Interceptor, so the final product differs a bit from my initial one...Enough gibberish, you can see a very very comprehensible example on this on Ayende's website. Big props for his great tutorial!
I'm working on a framework extension which handles dynamic injection using Ninject as the IoC container, but I'm having some trouble trying to work out how to achieve this.
The expectation of my framework is that you'll pass in the IModule(s) so it can easily be used in MVC, WebForms, etc. So I have the class structured like this:
public class NinjectFactory : IFactory, IDisposable {
readonly IKernel kernel;
public NinjectFactory(IModule[] modules) {
kernel = new StandardKernel(modules);
}
}
This is fine, I can create an instance in a Unit Test and pass in a basic implementation of IModule (using the build in InlineModule which seems to be recommended for testing).
The problem is that it's not until runtime that I know the type(s) I need to inject, and they are requested through the framework I'm extending, in a method like this:
public IInterface Create(Type neededType) {
}
And here's where I'm stumped, I'm not sure the best way to check->create (if required)->return, I have this so far:
public IInterface Create(Type neededType) {
if(!kernel.Components.Has(neededType)) {
kernel.Components.Connect(neededType, new StandardBindingFactory());
}
}
This adds it to the components collection, but I can't work out if it's created an instance or how I create an instance and pass in arguments for the .ctor.
Am I going about this the right way, or is Ninject not even meant to be be used that way?
Unless you want to alter or extend the internals of Ninject, you don't need to add anything to the Components collection on the kernel. To determine if a binding is available for a type, you can do something like this:
Type neededType = ...;
IKernel kernel = ...;
var registry = kernel.Components.Get<IBindingRegistry>();
if (registry.Has(neededType)) {
// Ninject can activate the type
}
Very very late answer but Microsoft.Practices.Unity allows Late Binding via App.Config
Just in case someone comes across this question