I am new to the MVVM architecture in Android, and I have some days with a doubt that I consider basic, but that I can't solve.
I proceed to discuss my problem:
I have an Entity, CustomerView (this entity is created from a DatabaseView):
#DatabaseView("select ... ")
public class CustomerView {
public String cardCode;
public String cardName;
public String cardFName;
...
Then, I have a Dao class:
#Dao
public interface OCRD_DAO {
...
#Query("SELECT * from CustomerView where cardCode= :cardCode")
LiveData<CustomerView> getCustomerViewByCardCode(String cardCode);
...
}
The repository class, makes use of the DAO class:
public LiveData<CustomerView> getCustomer(String cardCode){
return mOcrdDao.getCustomerViewByCardCode(cardCode);
}
The CustomerSheetViewModel class:
public class CustomerSheetViewModel extends BaseObservable {
private Repository mRepository;
public LiveData<CustomerView> mCustomer;
private MutableLiveData<String> _cardName;
#Bindable
public MutableLiveData<String> getCardName(){
return this._cardName;
}
public MutableLiveData<String> setCardName(String value){
// Avoids infinite loops.
if (mCustomer.getValue().cardName != value) {
mCustomer.getValue().cardName = value;
// React to the change.
saveData();
// Notify observers of a new value.
notifyPropertyChanged(BR._cardName);
}
}
public CustomerSheetViewModel (Application application, String cardCode) {
mRepository = new Repository(application);
this.mCustomer = mRepository.getCustomer(cardCode);
//Init MutableLiveData????
this._cardName = this.mCustomer.getValue().cardName;
//Null Exception, because this.mCustomer.getValue() is null
}
}
At this point, my problem occurs: when I initialise the CustomerView object, it is of type LiveData. However, if I want to make use of 2-way binding, I need an object of type MutableLiveData. So, I think I should create the MutableLiveData object with the data extracted from the database (i.e. from the call to the repository). When I try this (e.g. getValue().cardName) a null exception is thrown, since LiveData is asynchronous.
Finally, I could make use of this property in the layout:
android:text="#={customerSheetViewModel.cardName}"
I really appreciate any help, as I can't find any reference to 2-way binding when the data comes from a database read.
Thanks in advance.
Related
I have a question concerning the representation model processors of Spring HATEOAS. We are experimenting to process models before serializing them to the client. Our use case is to enrich the imageUrl field of UserModel objects at runtime, as we have to build the URL based on values from a config bean (AWS S3 bucket URL differs for DEV / PROD setup).
#Data
public class UserModel {
// ...
private String imageUrl;
}
Therefore, we create a UserProcessor to implement this:
public class UserProcessor implements RepresentationModelProcessor<EntityModel<UserModel>> {
private final ConfigAccessor configAccessor;
public UserProcessor(ConfigAccessor configAccessor) {
this.configAccessor = configAccessor;
}
#Override
public EntityModel<UserModel> process(EntityModel<UserModel> model) {
if (model.getContent() != null)
// do the enrichment and set "imageUrl" field
}
return model;
}
}
This works perfectly if we have a controller method like this:
#ResponseBody
#GetMapping("/me")
public EntityModel<UserModel> getCurrentUser(#AuthenticationPrincipal Principal principal) {
UserModel user = ... // get user model
return EntityModel.of(user);
}
However, we are struggling now with the enrichment whenever a UserModel is referenced in another model class, e.g., the BookModel:
#Data
public class BookModel {
private String isbn;
// ...
private EntityModel<UserModel> user; // or "private UserModel user;"
}
A controller method returning type EntityModel<BookModel> only applies the processor for its type, but not for types that are referenced. It seems the processors are not applied recursively.
Is this intentional or are we doing something wrong?
Thanks for any input and help,
Michael
I encountered the same issue and I resolved it by manually assembling resources, in your case that would be implementing RepresentationModelAssembler of the BookModel and then manually invoking the processor on the userModel object that is inside the book.
Make the outer resource a representation model
First consider the BookModel to extend RepresentationModel so that you can manually add links and assemble inner resources (which you would like for the EntityModel<UserModel> object)
#Data
public class BookModel extends RepresentationModel<BookModel> {...}
Write a model assembler
Now write the assembler that takes your book entity and transforms it into a representation model or a collection of these models. You will implement here what EntityModel.of(...) does for you automagically.
#Component
public class BookModelAssembler implements RepresentationModelAssembler<Book, BookModel> {
#Autowired
private UserProcessor userProcessor;
#Override
public BookModel toModel(Book entity) {
var bookModel = new BookModel(entity) // map fields from entity to model
// Transform the user entity to an entity model of user
var user = entity.getUser();
EntityModel<UserModel> userModel = EntityModel.of(user);
userModel = userProcessor.process(userModel);
bookModel.setUserModel(userModel);
return bookModel;
}
}
I might be going out on a limb but I suppose the reason for this is that the processors get invoked when an MVC endpoint returns a type that has a registered processor, which in the case of embedded types is not invoked. My reasoning is based on the docs for RepresentationModelProcessor, which states that processor processes representation models returned from Spring MVC controllers.
I am wondering what is the purpose of org.springframework.beans.factory.config.Scope.resolveContextualObject(String key) and org.springframework.beans.factory.config.Scope.getConversationId()?
From the javadoc:
Object resolveContextualObject(String key)
Resolve the contextual object for the given key, if any. E.g. the HttpServletRequest object for key "request".
String getConversationId()
Return the conversation ID for the current underlying scope, if any.
The exact meaning of the conversation ID depends on the underlying storage mechanism. In the case of session-scoped objects, the conversation ID would typically be equal to (or derived from) the session ID; in the case of a custom conversation that sits within the overall session, the specific ID for the current conversation would be appropriate.
This description doesn't tell me much.
Could you give me some examples which demonstrate how to make use of these methods?
My observation is that resolveContextualObject(String key) looks like a code smell, where where a Scope can expose some internal object.
Having:
public class MyCustomScope implements Scope {
private Pair<String, String> myPair;
#Override
public Object resolveContextualObject(String key) {
if ("myKey".equals(key)) return myPair;
return null;
}
// ...
}
#Configuration
public class RegisterMyScopeConfig {
#Bean
public BeanFactoryPostProcessor beanFactoryPostProcessor() {
return beanFactory -> beanFactory.registerScope(
"mycustomscope", new MyCustomScope());
}
}
Then you can:
#Scope("mycustomscope")
#Component
class MyComponent {
#Value("#{myKey.first}")
private String firstOfMyPair;
// or
#Value("#{myKey}")
private Pair<String,String> myPair;
}
Of course the way how you resolved object which matches key, might be fancier ;).
For example, in GenericScope it looks like that:
#Override
public Object resolveContextualObject(String key) {
Expression expression = parseExpression(key);
return expression.getValue(this.evaluationContext, this.beanFactory);
}
I am looking for transportation layer for gwt. I would like to create ajax request using generic method, f.e this is my DAO/service:
public class GenericDao<T extends GenericModel<T>> {
private Logger logger = LoggerFactory.getLogger(this.getClass().getCanonicalName());
#Transient protected Class<T> entityClass;
public GenericDao() {
super();
}
public GenericDao(Class<? extends GenericModel<T>> clazz) {
this.entityClass = (Class<T>) clazz;
}
public T getBy(Long id) {
return JPA.em().find(entityClass, id);
}
public List<GenericModel<T>> get() {
logger.error("trying to get data from db");
return getList();
}
public List<GenericModel<T>> getList() {
return JPA.em().createQuery("FROM " + entityClass.getSimpleName()).getResultList();
}
public void save(GenericModel<T> entityClass) {
JPA.em().getTransaction().begin();
JPA.em().persist(entityClass);
JPA.em().getTransaction().commit();
}
public void update(T entityClass) {
JPA.em().getTransaction().begin();
JPA.em().merge(entityClass);
JPA.em().getTransaction().commit();
}
public void delete(T entityClass) {
JPA.em().getTransaction().begin();
JPA.em().remove(entityClass);
JPA.em().getTransaction().commit();
}
}
GenericModel/Entity:
#MappedSuperclass
public class GenericModel<T extends GenericModel<T>> implements Identifiable, Versionable {
#Transient
protected Class<T> entityClass;
#Id
#GeneratedValue(strategy = GenerationType.IDENTITY)
private Long id;
#Version
private Integer version;
// setter & getter
#Override
public Long getId() {return id;}
public void setId(Long id) {this.id = id;}
#Override
public Integer getVersion() {return version;}
public void setVersion(Integer version) {this.version = version;}
// constructor
public GenericModel() {
Class<?> obtainedClass = getClass();
Type genericSuperclass = null;
for (;;) {
genericSuperclass = obtainedClass.getGenericSuperclass();
if (genericSuperclass instanceof ParameterizedType) {
break;
}
obtainedClass = obtainedClass.getSuperclass();
}
ParameterizedType genericSuperclass_ = (ParameterizedType) genericSuperclass;
try {
entityClass = ((Class) ((Class) genericSuperclass_
.getActualTypeArguments()[0]));
} catch (ClassCastException e) {
entityClass = guessEntityClassFromTypeParametersClassTypedArgument();
}
}
public GenericModel(Long id) {
this();
this.id = id;
}
}
I am looking for mechanism that will allow me to use this generic service for all models on client side (each db entity have id- so I would like to downloads using ajax all my Entities this way, so I should have only one generic method for that on client side).
I've already checked:
GWT-RPC
RequestFactory
RestyGWT
But none of them support this feature.
I've found here:
https://www.mail-archive.com/google-web-toolkit#googlegroups.com/msg100095.html
information that: gwt-jackson supports generics and polymorphism. Unfortunately I didn't found any working example that. Can someone help, give an example, approved that information?
All entities have id and version parameter. So I would like to have one metod on client side RF that will allow me to get from server(service/dao/whatever) that entity by id- like this: Request getBy(Long id); But unfortunatelly I can't make it work. I like the RF way, so I've tried it first. Generally I don't wonna repeat code for downloading entity/proxy by id.
For better understanding, please look also on:
RequestFactory client-side inheritance of typed class with generics
I'm confused as to why you think RPC can't handle generics - according to your link, it can, but RestyGWT cannot. Granted, none of your JPA references make any sense in GWT, but those would live in a DAO on the server, not in the entity/model class themselves, or at least not in the client version. If you had a RPC method that returned T where <T extends GenericModel<T>>, then you would have serializers for every possible GenericModel<?> subtype, and any/all that are gwt-compatible could be sent over the wire.
Edit from update to question:
Your GenericModel class uses features of Java that cannot work in GWT, such as reflection. This cannot be compiled to GWT, since the compiler relies on removing reflection information to minimize your compiled size - leaving in general reflection information means leaving in details about all classes and members, even ones that it can't statically prove are in use, since some reflection might make use of them.
If there is a way to phrase your model object in a way that just deals with the data at hand, focus on that. Otherwise consider a DTO which is just the data to send over the wire - I'm not sure how you would plan to use the entityClass field on the client, or why that would be important to read from the superclass's generics instead of just using getClass().
RequestFactory will have a hard time dealing with generics - unlike RPC (and possibly RestyGWT) it cannot handle polymorphism the way you want, but will instead only send the fields for the declared type, not any arbitrary subtype. RPC will actually send the instance if it is something that the client can handle.
I'm trying to setup a base Repository class that can use the Entity Framework edmx model context. The problem I'm having is that I need to find an interface that the EF EDMX object context implements so I can pass to the constructor via dependency injections. I've got around this before by using a DataFactory that creates it and stores it in the HttpContext but that kills the ability to unit test. Any help would be appreciated. Thanks!
public abstract class BaseRepository<T> where T : EntityObject
{
private MyDataModelContext _dataContext;
private ObjectSet<T> dbset;
protected BaseRepository(IObjectContext dataContext)
{
_dataContext = dataContext;
dbset = _dataContext.CreateObjectSet<T>();
}
.....
I've always created a DataContextFactory that passes my own interface to the Context, and passed that to my repositories like so:
The context interface:
public IMyDataContext {
// One per table in the database
IDbSet<Class1> Class1s { get;set; }
// etc
// The standard methods from EF you'll use
void Add( object Entity );
void Attach( object Entity );
void Delete( object Entity );
void SaveChanges();
}
The context factory:
public class MyDataContextFactory : IMyDataContextFactory {
public IMyDataContext GetContext() {
// TODO: Use the service locator pattern to avoid the direct instanciation
return new MyDataContext();
}
}
The context factory interface:
public interface IMyDataContextFactory {
IMyDataContext GetContext();
}
The repository:
public class MyClass1Repository {
private readonly IMyDataContextFactory factory;
public MyClass1Repository( IMyDataContextFactory Factory ) {
// TODO: check for null
this.factory = Factory;
}
public List<MyClass1> GetAll() {
using ( IMyDataContext db = this.factory.GetContext() ) {
return db.Class1s.ToList();
}
}
// TODO: Other methods that get stuff
}
Then when I want to test the repository, I pass in a fake IMyDataContextFactory that returns a fake IMyDataContext from GetContext().
In time I notice duplication in repositories, and can push certain methods into the base repository: GetAll(), Save(), GetById() sometimes if I have consistent primary keys, etc.
I have a repository pattern i created on top of the ado.net entity framework. When i tried to implement StructureMap to decouple my objects, i kept getting StackOverflowException (infinite loop?). Here is what the pattern looks like:
IEntityRepository where TEntity : class
Defines basic CRUD members
MyEntityRepository : IEntityRepository
Implements CRUD members
IEntityService where TEntity : class
Defines CRUD members which return common types for each member.
MyEntityService : IEntityService
Uses the repository to retrieve data and return a common type as a result (IList, bool and etc)
The problem appears to be with my Service layer. More specifically with the constructors.
public PostService(IValidationDictionary validationDictionary)
: this(validationDictionary, new PostRepository())
{ }
public PostService(IValidationDictionary validationDictionary, IEntityRepository<Post> repository)
{
_validationDictionary = validationDictionary;
_repository = repository;
}
From the controller, i pass an object that implements IValidationDictionary. And i am explicitly calling the second constructor to initialize the repository.
This is what the controller constructors look like (the first one creates an instance of the validation object):
public PostController()
{
_service = new PostService(new ModelStateWrapper(this.ModelState));
}
public PostController(IEntityService<Post> service)
{
_service = service;
}
Everything works if i don't pass my IValidationDictionary object reference, in which case the first controller constructor would be removed and the service object would only have one constructor which accepts the repository interface as the parameter.
I appreciate any help with this :) Thanks.
It looks like the circular reference had to do with the fact that the service layer was dependent on the Controller's ModelState and the Controller dependent on the Service layer.
I had to rewrite my validation layer to get this to work. Here is what i did.
Define generic validator interface like below:
public interface IValidator<TEntity>
{
ValidationState Validate(TEntity entity);
}
We want to be able to return an instance of ValidationState which, obviously, defines the state of validation.
public class ValidationState
{
private readonly ValidationErrorCollection _errors;
public ValidationErrorCollection Errors
{
get
{
return _errors;
}
}
public bool IsValid
{
get
{
return Errors.Count == 0;
}
}
public ValidationState()
{
_errors = new ValidationErrorCollection();
}
}
Notice that we have an strongly typed error collection which we need to define as well. The collection is going to consist of ValidationError objects containing the property name of the entity we're validating and the error message associated with it. This just follows the standard ModelState interface.
public class ValidationErrorCollection : Collection<ValidationError>
{
public void Add(string property, string message)
{
Add(new ValidationError(property, message));
}
}
And here is what the ValidationError looks like:
public class ValidationError
{
private string _property;
private string _message;
public string Property
{
get
{
return _property;
}
private set
{
_property = value;
}
}
public string Message
{
get
{
return _message;
}
private set
{
_message = value;
}
}
public ValidationError(string property, string message)
{
Property = property;
Message = message;
}
}
The rest of this is StructureMap magic. We need to create validation service layer which will locate validation objects and validate our entity. I'd like to define an interface for this, since i want anyone using validation service to be completely unaware of the StructureMap presence. Besides, i think sprinkling ObjectFactory.GetInstance() anywhere besides the bootstrapper logic a bad idea. Keeping it centralized is a good way to insure good maintainability. Anyway, i use the decorator pattern here:
public interface IValidationService
{
ValidationState Validate<TEntity>(TEntity entity);
}
And we finally implement it:
public class ValidationService : IValidationService
{
#region IValidationService Members
public IValidator<TEntity> GetValidatorFor<TEntity>(TEntity entity)
{
return ObjectFactory.GetInstance<IValidator<TEntity>>();
}
public ValidationState Validate<TEntity>(TEntity entity)
{
IValidator<TEntity> validator = GetValidatorFor(entity);
if (validator == null)
{
throw new Exception("Cannot locate validator");
}
return validator.Validate(entity);
}
#endregion
}
I'm going to be using validation service in my controller. We could move it to the service layer and have StructureMap use property injection to inject an instance of controller's ModelState to the service layer, but i don't want the service layer to be coupled with ModelState. What if we decide to use another validation technique? This is why i'd rather put it in the controller. Here is what my controller looks like:
public class PostController : Controller
{
private IEntityService<Post> _service = null;
private IValidationService _validationService = null;
public PostController(IEntityService<Post> service, IValidationService validationService)
{
_service = service;
_validationService = validationService;
}
}
Here i am injecting my service layer and validaton service instances using StructureMap. So, we need to register both in StructureMap registry:
ForRequestedType<IValidationService>()
.TheDefaultIsConcreteType<ValidationService>();
ForRequestedType<IValidator<Post>>()
.TheDefaultIsConcreteType<PostValidator>();
That's it. I don't show how i implement my PostValidator, but it's simply implementing IValidator interface and defining validation logic in the Validate() method. All that's left to do is call your validation service instance to retrieve the validator, call the validate method on your entity and write any errors to ModelState.
[AcceptVerbs(HttpVerbs.Post)]
public ActionResult Create([Bind(Exclude = "PostId")] Post post)
{
ValidationState vst = _validationService.Validate<Post>(post);
if (!vst.IsValid)
{
foreach (ValidationError error in vst.Errors)
{
this.ModelState.AddModelError(error.Property, error.Message);
}
return View(post);
}
...
}
Hope i helped somebody out with this :)
I used a similar solution involving a generic implementor of IValidationDictionary uses a StringDictionary and then copied the errors from this back into the model state in the controller.
Interface for validationdictionary
public interface IValidationDictionary
{
bool IsValid{get;}
void AddError(string Key, string errorMessage);
StringDictionary errors { get; }
}
Implementation of validation dictionary with no reference to model state or anything else so structuremap can create it easily
public class ValidationDictionary : IValidationDictionary
{
private StringDictionary _errors = new StringDictionary();
#region IValidationDictionary Members
public void AddError(string key, string errorMessage)
{
_errors.Add(key, errorMessage);
}
public bool IsValid
{
get { return (_errors.Count == 0); }
}
public StringDictionary errors
{
get { return _errors; }
}
#endregion
}
Code in the controller to copy the errors from the dictionary into the model state. This would probably be best as an extension function of Controller.
protected void copyValidationDictionaryToModelState()
{
// this copies the errors into viewstate
foreach (DictionaryEntry error in _service.validationdictionary.errors)
{
ModelState.AddModelError((string)error.Key, (string)error.Value);
}
}
thus bootstrapping code is like this
public static void BootstrapStructureMap()
{
// Initialize the static ObjectFactory container
ObjectFactory.Initialize(x =>
{
x.For<IContactRepository>().Use<EntityContactManagerRepository>();
x.For<IValidationDictionary>().Use<ValidationDictionary>();
x.For<IContactManagerService>().Use<ContactManagerService>();
});
}
and code to create controllers is like this
public class IocControllerFactory : DefaultControllerFactory
{
protected override IController GetControllerInstance(RequestContext requestContext, Type controllerType)
{
return (Controller)ObjectFactory.GetInstance(controllerType);
}
}
Just a quick query on this. It's helped me out quite a lot so thanks for putting the answer up, but I wondered which namespace TEntity exists in? I see Colletion(TEntity) needs System.Collections.ObjectModel. My file compiles without anything further but I see your TEntity reference highlighted in Blue which suggests it has a class type, mine is Black in Visual Studio. Hope you can help. I'm pretty keen to get this working.
Have you found any way to seperate validation into the service layer at all? My gut tells me that validating in the Controller is a bit smelly but I've looked high and low to find a way to pass validation error messages back to the controller without tightly coupling the service layer to the controller and can't find anything. :(
Again, thanks for the great post!
Lloyd