I need to know in my Repository whether I have internet connection or not (DB or API), so in my AppModule I use:
#InstallIn(SingletonComponent::class)
#Module
object AppModule {
#Singleton
#Provides
fun provideRepository(api: Api, dao: Dao, internetConn: Boolean) = Repository(api, dao, internetConn)
#Singleton
#Provides
fun provideInternetConnection(#ApplicationContext context: Context): Boolean {
return NetworkUtils().isInternetAvailable(context)
}
}
Hilt knows that the internetConn in the provideRepository params is the fun provideInternetConnection because of the return value (I guess).
But what if I want to create another provider with Boolean return value as well?
It's not working when I create another Singleton provider with Boolean return value.
I suggest you not inject something that might change over time. Instead inject the this class that performs this check and call the function where needed. What you have now, will check for network only once while building the dependency graph.
However it is possible to get a new value is if you inject Provider<Boolean> instead the boolean on its own. Provider will always evaluate the function that is providing the instance, there fore you'll have new value each call of isInternetAvaialbleProvider.get() is called.
Related
I'm building REST API on the top of Spring Data Rest. Initially all repositories where extending JpaRepository. Lately decision has been made to take a more flexible approach and use QueryDslPredicateExecutor<T> along with QuerydslBinderCustomizer<Q>.
Pretty much all findAll methods exposed in repositories should address two scenarios
principal has a role ROLE_ADMIN then no filtering should be applied a part from Pageable,Sort
principal does not have a role ROLE_ADMIN I would return only those entities which belong to the current user
Getting that done was as simple as annotating findAll method as below.
#Query("select e from Entity e where e.field = ?#{principal} or 1=?#{hasRole('ROLE_ADMIN') ? 1 : 0}")
Page<Entity> findAll(Pageable pageable);
Now I want our findAll to be something similar to below
Page<Entity> findAll(Predicate predicate, Pageable pageable)
Predicate is being build from request parameters(courtesy of #QuerydslPredicate) and is being passed in to RepositoryEntityController which is all being managed by spring-data-rest which is great.
#ResponseBody
#RequestMapping(value = BASE_MAPPING, method = RequestMethod.GET)
public Resources<?> getCollectionResource(#QuerydslPredicate RootResourceInformation resourceInformation,
DefaultedPageable pageable, Sort sort, PersistentEntityResourceAssembler assembler)
throws ResourceNotFoundException, HttpRequestMethodNotSupportedException {
I want to tweak that predicate(2 scenarios as above that I want to address).
It would be something simialr to below.
BooleanBuilder builder = new BooleanBuilder(predicateBuildFromHttpRequest);
builder.and(predicateAddressingOurRequirements);
builder.getValue();
#PostFilter won't be an option as return type for all repos is Page<Entity>.
Use case that I want to address seems to be quite common to me. Having said that I had a look at spring-data and spring-data-rest documentation and could not find anything related to my question.
Question is : Am I missing something obvious here and there is a quick win for it? or I would need to implement custom solution myself? Any comments very much appreciated!
The Querydsl predicates are constructed by QuerydslAwareRootResourceInformationHandlerMethodArgumentResolver which is sadly package private and can't be directly extended.
However, you can make a copy of that, add your security predicate logic and then drop in your implementation instead of the former resolver.
public class MyQueryDslRootResourceArgumentResolver extends RootResourceInformationHandlerMethodArgumentResolver {
// the most of the code is ommitted, the content is identical with
// QuerydslAwareRootResourceInformationHandlerMethodArgumentResolver,
// the important part is postProcessMethod where you can modify the predicate
#Override
#SuppressWarnings({"unchecked"})
protected RepositoryInvoker postProcess(MethodParameter parameter, RepositoryInvoker invoker,
Class<?> domainType, Map<String, String[]> parameters) {
Object repository = repositories.getRepositoryFor(domainType);
if (!QueryDslPredicateExecutor.class.isInstance(repository)
|| !parameter.hasParameterAnnotation(QuerydslPredicate.class)) {
return invoker;
}
ClassTypeInformation<?> type = ClassTypeInformation.from(domainType);
QuerydslBindings bindings = factory.createBindingsFor(null, type);
// modify your predicate here
Predicate predicate = predicateBuilder.getPredicate(type, toMultiValueMap(parameters), bindings);
return new QuerydslRepositoryInvokerAdapter(invoker, (QueryDslPredicateExecutor<Object>) repository, predicate);
}
}
Then add you own configuration class with the custom resolver implementation.
public class CustomRepositoryRestMvcConfiguration extends RepositoryRestMvcConfiguration {
#Autowired
ApplicationContext applicationContext;
#Override
public RootResourceInformationHandlerMethodArgumentResolver repoRequestArgumentResolver() {
QuerydslBindingsFactory factory = applicationContext.getBean(QuerydslBindingsFactory.class);
QuerydslPredicateBuilder predicateBuilder = new QuerydslPredicateBuilder(defaultConversionService(),
factory.getEntityPathResolver());
return new MyQueryDslRootResourceArgumentResolver(repositories(),
repositoryInvokerFactory(defaultConversionService()), resourceMetadataHandlerMethodArgumentResolver(),
predicateBuilder, factory);
}
}
Here is an example project that modifies the Predicate (that is produced by the parameters from url) before passing it to the repository.
The demonstration of what David Siro explained above
https://github.com/yeldarxman/QueryDslPredicateModifier
I am trying to understand Components in Dagger 2. Here is an example:
#Component(modules = { MyModule.class })
public interface MyComponent {
void inject(InjectionSite injectionSite);
Foo foo();
Bar bar();
}
I understand what the void inject() methods do. But I don't understand what the other Foo foo() getter methods do. What is the purpose of these other methods?
Usage in dependent components
In the context of a hierarchy of dependent components, such as in this example, provision methods such as Foo foo() are for exposing bindings to a dependent component. "Expose" means "make available" or even "publish". Note that the name of the method itself is actually irrelevant. Some programmers choose to name these methods Foo exposeFoo() to make the method name reflect its purpose.
Explanation:
When you write a component in Dagger 2, you group together modules containing #Provides methods. These #Provides methods can be thought of as "bindings" in that they associate an abstraction (e.g., a type) with a concrete way of resolving that type. With that in mind, the Foo foo() methods make the Component able to expose its binding for Foo to dependent components.
Example:
Let's say Foo is an application Singleton and we want to use it as a dependency for instances of DependsOnFoo but inside a component with narrower scope. If we write a naive #Provides method inside one of the modules of MyDependentComponent then we will get a new instance. Instead, we can write this:
#PerFragment
#Component(dependencies = {MyComponent.class }
modules = { MyDependentModule.class })
public class MyDependentComponent {
void inject(MyFragment frag);
}
And the module:
#Module
public class MyDepedentModule {
#Provides
#PerFragment
DependsOnFoo dependsOnFoo(Foo foo) {
return new DependsOnFoo(foo);
}
}
Assume also that the injection site for DependentComponent contains DependsOnFoo:
public class MyFragment extends Fragment {
#Inject DependsOnFoo dependsOnFoo
}
Note that MyDependentComponent only knows about the module MyDependentModule. Through that module, it knows it can provide DependsOnFoo using an instance of Foo, but it doesn't know how to provide Foo by itself. This happens despite MyDependentComponent being a dependent component of MyComponent. The Foo foo() method in MyComponent allows the dependent component MyDependentComponent to use MyComponent's binding for Foo to inject DependsOnFoo. Without this Foo foo() method, the compilation will fail.
Usage to resolve a binding
Let's say we would like to obtain instances of Foo without having to call inject(this). The Foo foo() method inside the component will allow this much the same way you can call getInstance() with Guice's Injector or Castle Windsor's Resolve. The illustration is as below:
public void fooConsumer() {
DaggerMyComponent component = DaggerMyComponent.builder.build();
Foo foo = component.foo();
}
Dagger is a way of wiring up graphs of objects and their dependencies. As an alternative to calling constructors directly, you obtain instances by requesting them from Dagger, or by supplying an object that you'd like to have injected with Dagger-created instances.
Let's make a coffee shop, that depends on a Provider<Coffee> and a CashRegister. Assume that you have those wired up within a module (maybe to LightRoastCoffee and DefaultCashRegister implementations).
public class CoffeeShop {
private final Provider<Coffee> coffeeProvider;
private final CashRegister register;
#Inject
public CoffeeShop(Provider<Coffee> coffeeProvider, CashRegister register) {
this.coffeeProvider = coffeeProvider;
this.register = register;
}
public void serve(Person person) {
cashRegister.takeMoneyFrom(person);
person.accept(coffeeProvider.get());
}
}
Now you need to get an instance of that CoffeeShop, but it only has a two-parameter constructor with its dependencies. So how do you do that? Simple: You tell Dagger to make a factory method available on the Component instance it generates.
#Component(modules = {/* ... */})
public interface CoffeeShopComponent {
CoffeeShop getCoffeeShop();
void inject(CoffeeService serviceToInject); // to be discussed below
}
When you call getCoffeeShop, Dagger creates the Provider<Coffee> to supply LightRoastCoffee, creates the DefaultCashRegister, supplies them to the Coffeeshop constructor, and returns you the result. Congratulations, you are the proud owner of a fully-wired-up coffeeshop.
Now, all of this is an alternative to void injection methods, which take an already-created instance and inject into it:
public class CoffeeService extends SomeFrameworkService {
#Inject CoffeeShop coffeeShop;
#Override public void initialize() {
// Before injection, your coffeeShop field is null.
DaggerCoffeeShopComponent.create().inject(this);
// Dagger inspects CoffeeService at compile time, so at runtime it can reach
// in and set the fields.
}
#Override public void alternativeInitialize() {
// The above is equivalent to this, though:
coffeeShop = DaggerCoffeeShopComponent.create().getCoffeeShop();
}
}
So, there you have it: Two different styles, both of which give you access to fully-injected graphs of objects without listing or caring about exactly which dependencies they need. You can prefer one or the other, or prefer factory methods for the top-level and members injection for Android or Service use-cases, or any other sort of mix and match.
(Note: Beyond their use as entry points into your object graph, no-arg getters known as provision methods are also useful for exposing bindings for component dependencies, as David Rawson describes in the other answer.)
I have a class that serves as a model for some data I get from a server. This data starts as an unwieldy xml object where text nodes have attributes so the json format I convert it into does not have simple string values. Instead I have:
#Injectable()
export class FooString {
_attr: string;
value: string;
isReadOnly(): boolean {
return this._attr && this._attr === 'ReadOnly';
}
isHidden(): boolean {
return this._attr && this._attr === 'Hid';
}
}
Then my model is like:
#Injectable()
export class Payment {
constructor(
public FooId: FooString,
public FooStat: FooString,
public FooName: FooString ) { }
}
Everything ends up with the same instance of FooString. How do I get discrete instances for each of them?
I have tried a factory, but it still only creates a single instance:
export let fooStringProvider = provide(FooString, {
useFactory: (): FooString => {
console.log('in foostring factory');
return new FooString();
}
});
new FooString();
new Payment();
;-)
Why using DI when they don't have dependencies and you don't want to maintain single instances per provider. Therefore, just use new.
When to use DI
There are a few criterias when using DI instead of new the right thing:
If you want Angular to maintain and share instances
If you want to work with an interface or base class but then you want to configure from the outside what implementation should actually be used at runtime - like the MockBackend for Http during testing.
If you class has dependencies to instances and/or values provided by DI
If you want to be able to easily test classes in isolation (https://en.wikipedia.org/wiki/Inversion_of_control)
probably others ...
If there are good arguments to use DI, but you also want new instances then you can just provide a factory.
This answer https://stackoverflow.com/a/36046754/217408 contains a concrete example how to do that.
Using DI is usually a good idea. There are IMHO no strong arguments against using DI. Only when none of the above arguments apply and providing factories is too cumbersome, use new Xxx() instead.
I'm trying to add Dagger to an existing web application and am running into a design problem.
Currently our Handlers are created in a dispatcher with something like
registerHandler('/login', new LoginHandler(), HttpMethod.POST)
Inside the login handler we might call a function like
Services.loginService.login('username', 'password');
I want to be able to inject the loginService into the handler, but am having trouble figuring out the best approach. There is a really long list of handlers in the dispatcher, and injecting them all as instance variables seems like a large addition of code.
Is there a solution to this type of problem?
Based on your comment about having different services to inject. I would propose next solution.
ServicesProvider:
#Module(injects = {LoginHandler.class, LogoutHandler.class})
public class ServicesProvider {
#Provides #Singleton public LoginService getLoginService() {
return new LoginService();
}
}
LoginHandler.java:
public class LoginHandler extends Handler {
#Inject LoginService loginService;
}
HttpNetwork.java
public class HttpNetwork extends Network {
private ObjectGraph objectGraph = ObjectGraph.create(new ServicesProvider());
public registerHandler(String path, Handler handler, String methodType) {
getObjectGraph().inject(handler);
}
}
There is one week point in this solution - you can't easily change ServiceProvider for test purpose (or any other kind of purpose). But if you inject it also (for example with another object graph or just through constructor) you can fix this situation.
I previously had the following code, it works fine. (note that Card, SearchResults, Quiz all extend Persistable, and Persistable contains the constructor .fromMap.
Persistable fromString(String value){
Map<String, dynamic> m = parse(value);
switch(m['type']){
case 'card':
return new Card.fromMap(m);
case 'searchresults':
return new SearchResults.fromMap(m);
case 'quiz':
return new Quiz.fromMap(m);
}
}
It was a bit wordy, so I thought I would break it down into two parts. I first have this:
static final Map<String, Persistable> lookup =
{'card': Card,
'searchresults': SearchResults,
'quiz': Quiz };
Seems reasonable, but then when I try to redefine the method, I get confused.
Persistable fromString(String value){
Map<String, dynamic> m = parse(value);
String type = m['type'];
Persistable p = lookup[type];
... Confused, this can't be right
... ultimately want to "return new p.fromMap(m)";
}
Persistable p really means a instance of class Persistable. How do I type my lookup map so that its values are of the class Persistable, so that I can call their .fromMap constructors?
First of all I think your initial approach is perfectly valid and should not be cast away owing simply to its verbosity.
I believe alternative approaches introduce additional complexity and are justified only if you are really in need of dynamic dispatch. (For example if you write library for persistency and you wish to add ability to register arbitrary class for persistency for clients of library)
If dynamic dispatch is a must for you I believe there is two main possibility:
- Reflection API. Recently reflection library got sync API, so this way is now much more affordable then before. I believe there always will be some cost incurred by reflection anyway.
- Use core DART functionality.
With the second approach you may use some sort of trick to imitate constructor call dynamically.
For instance you may store in map not Type variable but function which returns instance of required class:
So your code may look something like
static final Map<String, Function> lookup = new Map<String, Function>
static void registerClass(String className, factory) {
lookup[className] = factory;
}
static Persistable getInstance(String className, Map map){
return lookup[className](map);
}
And on client side:
....
registerClass('quiz', (map)=> new Quiz.fromMap(map));
registerClass('card', (map)=> new Card.fromMap(map));
(Attention - I did not test this)
You may look for working sample code for that approach in https://github.com/vadimtsushko/objectory