I have a very simple problem of DI, and wanted to know if there is a way to solve it using Ninject (or any other DI helper).
I have a Data Access interface that is implemented by several Data Sources providers, like DB, Sharepoint, CRM, etc.
I want to use Ninject to get a specific instance of the interface, based on a parameter that contains a code representing one of this implementations.
So far I know that I can do that by using named bindings , but I couldn't find a way to do the same by xml config file (Ninject.extensions.xml).
Ninject extensions xml provides a way to solve single mappings:
<module name="SomeModule">
<bind service="Game.IWeapon" to="Game.Sword"/>
<bind service="Game.IWarrior" toProvider="Game.SamuraiProvider"/>
</module>
I'd like to do a config like that, but using multiple mappings for the same interface, using a name, a code or the like.
TIA,
Milton
Just add a name property
<bind service="Game.IWeapon" to="Game.Sword" name="sword"/>
<bind service="Game.IWeapon" to="Game.Dagger" name="dagger"/>
Related
This is more of a conceptual question.
I had to work on a functionality that had to create a dynamic h:dataTable. And whenever I created a component, I did something similar to this:
DataTable table = (DataTable) FacesContext.getCurrentInstance().getApplication()
.createComponent(DataTable.COMPONENT_TYPE);
Using the FacesContext to create everything for me.
However I could just as simply have done this:
DataTable table = new DataTable();
The reason I did it in the first way is that all the tutorials and material I read while developing did it that way, but I never got a clear answer why.
Is there an actual reason why the first is better than the second?
The Application#createComponent() adds an extra abstract layer allowing runtime polymorphism and pluggability. The concrete implementation is configurable by <component> entry in faces-config.xml which could in turn be provided via a JAR. This allows changing implementation without rewriting/recompiling the code.
It's exactly like as how JDBC API works: you don't do new SomeDriver(), but you do Class.forName(someDriverClassName) which allows the driver to not be a compiletime dependency and thus your JDBC code to be portable across many DB vendors without rewriting/recompiling.
However, if the application is for "internal usage" only and not intented to be distributable (and thus all the code is always full under you control), then runtime polymorphism has not a so big advantage and may add (very minor) overhead.
See also:
What is the relationship between component family, component type and renderer type?
I want to be able to use ninject to inject a different type of DBContext into different areas of my application. Does anyone know if you can do this with a ninject When clause?
Something along the lines of:
Bind<DbContext>().To<ServiceContext1>().When(t=>t.Target.Type.Assembly.FullName.StartsWith("Namespace.Context1."));
Bind<DbContext>().To<ServiceContext2>().When(t => t.Target.Type.Assembly.FullName.StartsWith("Namespace.Context2."));
Bind(typeof(IRepositoryDataSource<>)).To(typeof(DbContextRepositoryDataSource<>));
Bind(typeof(IRepository<>)).To(typeof(SimpleRepository<>));
request.Target.Type returns the parameter type. You are looking forrequest.Target.Member.ReflectedType. Since you inject the context into the identical repository you probably have to check on the parent request using request.ParentRequest or even the grand parent rather than on the request because there you will get always the repository type.
For instance I have this bit of code
public class ProductService{
private IProductDataSource _dataSource = DependencyManager.Get<IProductDataSource>();
public Product Get(int id){
return _dataSource.Select(id);
}
}
I have 2 different data source:
XML file which contains the informations only in 1 language,
a SQL data base which contains the informations in many languages.
So I created 2 implementation for IProductDataSource, for for each kind of datasource.
But how do I send the required language to the SQL data source ?
I add the parameter "language" to the method "IProductDataSource.Select" even if I won't use it in the case of the XML implementation.
Inside the SQL implementation I get the language from a global state ?
I add the language to the constructor of my SQL implementation, but then I won't use my DependencyManager and handle my self the dependency injection.
Maybe my first solution is not good.
The third option is the way to go. Inject the language configuration to your SQL implementation. Also get rid of your DependencyManager ServiceLocator and use constructor injection instead.
If your application needs to work with multiple languages in a single instance I think point one is a sensible approach. If the underlying data does not provide translations for a request language then return null. There is another solution in this scenario. I'm assuming that what you have is a list of products and language translations for each product. Can you refactor your model so that you do not need to specify or asertain the langauge until you reference language specific text? The point being a product is a product regardless of the language you choose to describe it. i.e. one product instance per product, only the product id on the Datasource.Select(..) method and some other abstraction mechanism to deal with accessing the correct text translation.
If however each instance of your application is only concerned with one language set I second Mr Gloor.
First of all I need to point out that you are NOT injecting any dependencies with your example - you are depending on a service locator (DependencyManager) to get them for you. Dependency injection, simply put, is when your classes are unaware of who provides the dependencies, e.g. using a constructor, a setter, a method. As it was already mentioned in the other answers, Service locator is an anti-pattern and should be avoided. The reasons are described in this great article.
Another thing is that the settings you are mentioning, such as language or currency, seem to be localization related and would probably be better dealt with using the built-in mechanisms of your language of choice (e.g. resource files, etc).
Now, having said that, depending on how the rest of your code is structured you have several options to solve this while still using Service locator:
You could have SqlDataSource depend on some ILanguageProvider which pulls the current language from somewhere. However, with more settings like these (or if it is difficult to get current language in an isolated way) this can get messy very fast.
You could depend on IProductDataSourceFactory instead (or, if you are using C#, Func<IProductDataSource>) which would return the concrete implementation with the correct settings. Again, you need to be able to get the current language in an isolated way in order to use this.
You could go with option 1 in your question. This would be a leaky abstraction but would be the simplest to implement.
However, if you decide to get rid of service locator and start using some DI container, the best solution would be using option 3 (as it was already stated) and configuring container accordingly to provide the correct value. Some good ideas of how to do this in an elegant way can be found in the answer to this question
This seems like a fundamental Web Services problem. However an elegant solution is elusive based on some research I have been able to do. I guess I am missing something here
I am using a WCF client to connect to a External web service of which I have no control. The external WS is java based. There are a bunch of assemblies which are provided to call the methods in web service. These assemblies have base classes and derived classes. The web service methods can take Base class as param whereas from the WCF Client I instantiate a Derived class and pass it to the method.
To simulate this scenario, I created a small project with one ClassLibrary which has a BaseClass and a DerivedClass with one method.
Then I create an asmx web service and add a HelloWorld method inside it. I add a reference to the ClassLibrary. This method takes a BaseClass type param.
Then I create a Service Reference to the ASMX web service. In the proxy class, I add a XmlSerializerFormatAttribute to the method if it is already not there.
From the WCF client, I call the ASMX web method
BaseClass bc = new Derived();
ServiceReference1.TestService ts = new WCFTest.ServiceReference1.TestService();
lbl1.Text = (c1.HelloWorld(bc));
The call fails with error
The type ClassLib.Derived was not expected. Use the XmlInclude or SoapInclude attribute to specify types that are not known statically.
The only way I could call this web service method was by adding XmlInclude attribute to the BaseClass in the ClassLibrary.
In my scenario, this library is a dll provided by an external vendor. I cannot add attributes to its classes. I have looked a DataContractSerializer and KnownTypes and XmlSerializer ctor. However those solutions do not seem to be applicable in my scenario.
How can I make XMLSerializer see the Derived classes in the assemblies I have referencing in the WCF Client? Is there an elegant solution?
Thanks,
Hem
Including your own type mapping for an XmlSerializerOperationBehavior may just work, but I haven't tried this (see GetXmlMappings).
http://msdn.microsoft.com/en-us/library/system.servicemodel.description.xmlserializeroperationbehavior.aspx
Alternatively, forcing use of the DataContractSerializer via a DataContractSerializerOperationBehavior (as opposed to the XmlSerializerOperationBehavior it's using now) may work too, if you specify your own known types
http://msdn.microsoft.com/en-us/library/ms576751%28v=vs.85%29.aspx
Finally, as a last resort, you can force use of the DataContractSerializer using the DataContractSerializerOperationBehavior, then specify your own DataContractSurrogate to force use of the XmlSerializer where you can pass custom types to its constructor (which circumvents the requirement for the XmlInclude attribute).
http://msdn.microsoft.com/en-us/library/ms751540.aspx
Hope that helps.
This is pretty much a duplicate question but instead of using Castle Dynamic Proxy I'm using LinFu Getting underlying type of a proxy object
I'm using automapper to create proxies of interfaces that I'm sending to my viewmodel in Asp.net MVC. My problem is from what I can tell that MVC's default MetadataProvider find the properties and metadata by calling .GetType() on the model.
So what happens is EditorFor() and DisplayFor() templates don't generate any fields. What I need to do is find the proxy target type and then generate my templates. I know I can just parse the name and use GetType( "thename" ) but was wondering if there was an easy way.
LinFu.DynamicProxy doesn't directly expose the underlying object of a proxy. It simply redirects each method call to an IInterceptor implementation instance. In order to access the underlying object, you'll have to figure out whether or not the current interceptor instance actually has a target class instance, or not.
If you're working with AutoMapper, AFAIK, they use LinFu.DynamicObject to do a lot of the duck taping, and calling GetType() on a dynamic type generated by LinFu.DynamicObject won't even get you the actual type in your domain model--it will just get you an object that has been literally duck-taped together by LinFu itself.
get latest AutoMapper - it uses Castle Dynamic Proxy, and you already know how to get this from there :)