Learning Dagger2 and maybe going off the rails here. I have a class - MapRoute that may or may not be needed in a Fragment. If MapRoute is needed, I want to create it and when the MapRoute is instantiated I want to inject it with dependencies created at the application level. I am also using Builder pattern to populate MapRouter.
Perhaps the generic question is when you are in nonAndroid classes (not Activity/Fragment/...) how can you inject dependencies from above? How to you construct the nonAndroid injector in place of AndroidInjection.inject(this)?
So my fragment is:
public class ActivityMapFragment extends DaggerFragment ... {
#Inject
MapRoute.Builder mapRouteBuilder;
private void plotRouteForMap(Cursor csr){
MapRoute.Builder builder = new MapRoute.Builder();
builder.setSupportMapFragment(supportMapFragment)
.setLocationExerciseRecord(ler)
.setMapType(mapType)
.setUseCurrentLocationLabel(useCurrentLocationLabel)
.setCursor(csr)
.setTitle(activityTitle)
.setActivityPhotosCallback(this);
mapRoute = builder.build();
mapRoute.plotGpsRoute();
}
...
MapRoute is: (Edit) added Builder code snippet
public class MapRoute ... {
#Inject
public DisplayUnits displayUnits; <<< Created at app level
#Inject
public PhotoUtils photoUtils; <<<< Create at app level
public MapRoute() {
// Use subcomponent builder
MapRouteSubcomponent component =
DaggerMapRouteSubComponent.builder().build(); <<< Want to do this
component.inject(this);
}
public static class Builder {
SupportMapFragment supportMapFragment;
LocationExerciseRecord ler;
boolean useCurrentLocationLabel;
int mapType;
Cursor cursor;
ActivityPhotosCallback activityPhotosCallback;
String title;
#Inject
public Builder() {
}
public Builder setSupportMapFragment(SupportMapFragment supportMapFragment){
this.supportMapFragment = supportMapFragment;
return this;
}
....
MapRouteSubcomponent best guess:
#Subcomponent(modules = {MapRouteModule.class, ApplicationModule.class})
public interface MapRouteSubcomponent {
// allow to inject into our MapRoute class
void inject(MapRoute mapRoute);
#Subcomponent.Builder
interface Builder extends SubComponentBuilder<MapRouteSubcomponent> {
Builder mapRouteModule(MapRouteModule mapRouteModule);
}
#Module
public class MapRouteModule {
// What to put here?
}
And finally a subcomponent builder:
// from https://github.com/Zorail/SubComponent/blob/master/app/src/main/java/zorail/rohan/com/subcomponent/SubComponentBuilder.java
public interface SubComponentBuilder<V> {
V build();
}
At this point I am at a stand on where to go from here.
The projects in my solution are set up like this:
App.Data
App.Models
App.Web
In App.Data, I'm using Entity Framework to access my data with a bunch of Repositories to abstract interaction with it. For obvious reasons, I would like my App.Web to reference only the App.Data project and not Entity Framework.
I'm using Constructor Injection to give my Controllers a reference to a Repository container that looks like this:
public interface IDataRepository
{
IUserRepository User { get; set; }
IProductRepository Product { get; set; }
// ...
}
public class DataRepository : IDataRepository
{
private readonly AppContext _context;
public DataRepository(AppContext context)
{
_context = context;
}
// ...
}
DataRepository will have a AppContext object (which inherits from Entity Framework's DbContext) that all the child Repositories will use to access the database.
So finally we come to my problem: how do I use Constructor Injection on DataRepository considering it's a code library and has no entry-point? I can't bootstrap AppContext in App.Web because then I have to reference Entity Framework from that project.
Or am I just doing something stupid?
You can define a RepositoryConnection class in App.Data that acts as a wrapper to the Context and removes the need to reference EF in App.Web. If you are using an IoC Container you can control the lifetime of the RepositoryConnection class to ensure that all instances of Repository get the same Context. This is a simplified example ...
public class RepositoryConnection
{
private readonly AppContext _context;
public RepositoryConnection()
{
_context = new AppContext();
}
public AppContext AppContext { get { return _context; } }
}
public class DataRepository : IDataRepository
{
private readonly AppContext _context;
public DataRepository(RepositoryConnection connection)
{
_context = connection.AppContext;
}
// ...
}
I have the following class:
public class MyClass {
#Inject
private MyAnotherClass myAnotherClass;
public MyClass() {
//Perform operations on myAnotherClass.
}
}
I need to do some things in constructor which require an instance of myAnotherClass. Unfortunately myAnotherClass is injected after code in constructor is ran, which means I am performing operations on null...
I could of course instantiate it the classic way (MyAnotherClass myAnotherClass = new MyAnotherClass()) directly in constructor, but I don't think it is the right thing to do in this situation.
What solutions would you suggest to solve this problem?
Best option:
public class MyClass {
private final MyAnotherClass myAnotherClass;
public MyClass(MyAnotherClass other) {
this.myAnotherClass = other;
// And so forth
}
}
T5-IoC will then use constructor injection so there's no need to 'new' up MyClass yourself. See Defining Tapestry IOC Services for more info.
Alternatively:
public class MyClass {
#Inject
private MyAnotherClass myAnotherClass;
#PostInjection
public void setupUsingOther() {
// Called last, after fields are injected
}
}
In my GWTP application I need to Inject HttpServletRequest, HttpSession as instance variable of ActionHandler.
My ActionHandler is initialized through Spring.
I can't get current Request object through Spring as it instantiates just POJO.
I am thinking about mixing GIN and Spring.
Would I be able inject HttpServletRequest using GIN in my ActionHandler which is instantiated through Spring?????
Is it possible to do following way??
#Configuration
#Import(DefaultModule.class)
public class ServerModule extends HandlerModule
{
#Bean
public UserVerficationActionHandler getUserVerificationActionActionHandler()
{
return new UserVerficationActionHandler();
}
}
public class UserVerficationActionHandler implements ActionHandler<UserVerficationAction, UserVerficationActionResult>
{
#Autowired
private UserService userService;
private Provider<HttpServletRequest> requestProvider;
#Inject
public UserVerficationActionHandler()
{
}
public UserVerficationActionResult execute(UserVerficationAction action, ExecutionContext context) throws ActionException
{
....
}
#Inject
public Provider<HttpServletRequest> setRequestProvider()
{
return requestProvider;
}
}
-------ActionHandler Ends--------
Can somebody let me know Is it possible to do SetterInjection this way?
Second thing, if above is possible then will I be getting current request object using this method?
Thanks in advance.
Bhavesh.
I'm using StructureMap to resolve references to my repository class. My repository interface implements IDisposable, e.g.
public interface IMyRepository : IDisposable
{
SomeClass GetById(int id);
}
An implementation of the interface using Entity Framework:
public MyRepository : IMyRepository
{
private MyDbContext _dbContext;
public MyDbContext()
{
_dbContext = new MyDbContext();
}
public SomeClass GetById(int id)
{
var query = from x in _dbContext
where x.Id = id
select x;
return x.FirstOrDefault();
}
public void Dispose()
{
_dbContext.Dispose();
}
}
Anyway as mentioned I'm using StructureMap to resolve IMyRepository. So when, where and how should I call my dispose method?
WARNING: please note that my views have changed, and you should consider the following advise outdated. Please see this answer for an updated view: https://stackoverflow.com/a/30287923/264697
While DI frameworks can manage lifetime of objects for you and some could even dispose objects for you after you're done using with them, it makes object disposal just too implicit. The IDisposable interface is created because there was the need of deterministic clean-up of resources. Therefore, in the context of DI, I personally like to make this clean-up very explicit. When you make it explicit, you've got basically two options: 1. Configure the DI to return transient objects and dispose these objects yourself. 2. Configure a factory and instruct the factory to create new instances.
I favor the second approach over the first, because especially when doing Dependency Injection, your code isn't as clean as it could be. Look for instance at this code:
public sealed class Client : IDisposable
{
private readonly IDependency dependency;
public Client(IDependency dependency)
{
this. dependency = dependency;
}
public void Do()
{
this.dependency.DoSomething();
}
public Dispose()
{
this.dependency.Dispose();
}
}
While this code explicitly disposes the dependency, it could raise some eyebrows to readers, because resources should normally only be disposed by the owner of the resource. Apparently, the Client became the owner of the resource, when it was injected.
Because of this, I favor the use of a factory. Look for instance at this example:
public sealed class Client
{
private readonly IDependencyFactory factory;
public Client(IDependencyFactory factory)
{
this.factory = factory;
}
public void Do()
{
using (var dependency = this.factory.CreateNew())
{
dependency.DoSomething();
}
}
}
This example has the exact same behavior as the previous example, but see how the Client class doesn't have to implement IDisposable anymore, because it creates and disposes the resource within the Do method.
Injecting a factory is the most explicit way (the path of least surprise) to do this. That's why I prefer this style. Downside of this is that you often need to define more classes (for your factories), but I personally don't mind.
RPM1984 asked for a more concrete example.
I would not have the repository implement IDisposable, but have a Unit of Work that implements IDisposable, controls/contains repositories and have a factory that knows how to create new unit of works. With that in mind, the above code would look like this:
public sealed class Client
{
private readonly INorthwindUnitOfWorkFactory factory;
public Client(INorthwindUnitOfWorkFactory factory)
{
this.factory = factory;
}
public void Do()
{
using (NorthwindUnitOfWork db =
this.factory.CreateNew())
{
// 'Customers' is a repository.
var customer = db.Customers.GetById(1);
customer.Name = ".NET Junkie";
db.SubmitChanges();
}
}
}
In the design I use, and have described here, I use a concrete NorthwindUnitOfWork class that wraps an IDataMapper that is the gateway to the underlying LINQ provider (such as LINQ to SQL or Entity Framework). In sumary, the design is as follows:
An INorthwindUnitOfWorkFactory is injected in a client.
The particular implementation of that factory creates a concrete NorthwindUnitOfWork class and injects a O/RM specific IDataMapper class into it.
The NorthwindUnitOfWork is in fact a type-safe wrapper around the IDataMapper and the NorthwindUnitOfWork requests the IDataMapper for repositories and forwards requests to submit changes and dispose to the mapper.
The IDataMapper returns Repository<T> classes and a repository implements IQueryable<T> to allow the client to use LINQ over the repository.
The specific implementation of the IDataMapper holds a reference to the O/RM specific unit of work (for instance EF's ObjectContext). For that reason the IDataMapper must implement IDisposable.
This results in the following design:
public interface INorthwindUnitOfWorkFactory
{
NorthwindUnitOfWork CreateNew();
}
public interface IDataMapper : IDisposable
{
Repository<T> GetRepository<T>() where T : class;
void Save();
}
public abstract class Repository<T> : IQueryable<T>
where T : class
{
private readonly IQueryable<T> query;
protected Repository(IQueryable<T> query)
{
this.query = query;
}
public abstract void InsertOnSubmit(T entity);
public abstract void DeleteOnSubmit(T entity);
// IQueryable<T> members omitted.
}
The NorthwindUnitOfWork is a concrete class that contains properties to specific repositories, such as Customers, Orders, etc:
public sealed class NorthwindUnitOfWork : IDisposable
{
private readonly IDataMapper mapper;
public NorthwindUnitOfWork(IDataMapper mapper)
{
this.mapper = mapper;
}
// Repository properties here:
public Repository<Customer> Customers
{
get { return this.mapper.GetRepository<Customer>(); }
}
public void Dispose()
{
this.mapper.Dispose();
}
}
What's left is an concrete implementation of the INorthwindUnitOfWorkFactory and a concrete implementation of the IDataMapper. Here's one for Entity Framework:
public class EntityFrameworkNorthwindUnitOfWorkFactory
: INorthwindUnitOfWorkFactory
{
public NorthwindUnitOfWork CreateNew()
{
var db = new ObjectContext("name=NorthwindEntities");
db.DefaultContainerName = "NorthwindEntities";
var mapper = new EntityFrameworkDataMapper(db);
return new NorthwindUnitOfWork(mapper);
}
}
And the EntityFrameworkDataMapper:
public sealed class EntityFrameworkDataMapper : IDataMapper
{
private readonly ObjectContext context;
public EntityFrameworkDataMapper(ObjectContext context)
{
this.context = context;
}
public void Save()
{
this.context.SaveChanges();
}
public void Dispose()
{
this.context.Dispose();
}
public Repository<T> GetRepository<T>() where T : class
{
string setName = this.GetEntitySetName<T>();
var query = this.context.CreateQuery<T>(setName);
return new EntityRepository<T>(query, setName);
}
private string GetEntitySetName<T>()
{
EntityContainer container =
this.context.MetadataWorkspace.GetEntityContainer(
this.context.DefaultContainerName, DataSpace.CSpace);
return (
from item in container.BaseEntitySets
where item.ElementType.Name == typeof(T).Name
select item.Name).First();
}
private sealed class EntityRepository<T>
: Repository<T> where T : class
{
private readonly ObjectQuery<T> query;
private readonly string entitySetName;
public EntityRepository(ObjectQuery<T> query,
string entitySetName) : base(query)
{
this.query = query;
this.entitySetName = entitySetName;
}
public override void InsertOnSubmit(T entity)
{
this.query.Context.AddObject(entitySetName, entity);
}
public override void DeleteOnSubmit(T entity)
{
this.query.Context.DeleteObject(entity);
}
}
}
You can find more information about this model here.
UPDATE December 2012
This an an update written two years after my original answer. The last two years much has changed in the way I try to design the systems I'm working on. Although it has suited me in the past, I don't like to use the factory approach anymore when dealing with the Unit of Work pattern. Instead I simply inject a Unit of Work instance into consumers directly. Whether this design is feasibly for you however, depends a lot on the way your system is designed. If you want to read more about this, please take a look at this newer Stackoverflow answer of mine: One DbContext per web request…why?
If you want to get it right, i'd advise on a couple of changes:
1 - Don't have private instances of the data context in the repository. If your working with multiple repositories then you'll end up with multiple contexts.
2 - To solve the above - wrap the context in a Unit of Work. Pass the unit of work to the Repositories via the ctor: public MyRepository(IUnitOfWork uow)
3 - Make the Unit of Work implement IDisposable. The Unit of Work should be "newed up" when a request begins, and therefore should be disposed when the request finishes. The Repository should not implement IDisposable, as it is not directly working with resources - it is simply mitigating them. The DataContext / Unit of Work should implement IDispoable.
4 - Assuming you are using a web application, you do not need to explicitly call dispose - i repeat, you do not need to explicitly call your dispose method. StructureMap has a method called HttpContextBuildPolicy.DisposeAndClearAll();. What this does is invoke the "Dispose" method on any HTTP-scoped objects that implement IDisposable. Stick this call in Application_EndRequest (Global.asax). Also - i believe there is an updated method, called ReleaseAllHttpScopedObjects or something - can't remember the name.
Instead of adding Dispose to IMyRepository, you could declare IMyRepository like this:
public interface IMyRepository: IDisposable
{
SomeClass GetById(int id);
}
This way, you ensure all repository will call Dispose sometimes, and you can use the C# "using" pattern on a Repository object:
using (IMyRepository rep = GetMyRepository(...))
{
... do some work with rep
}