In my ViewModel, I load data using
private val pagingConfig = PagedList.Config.Builder()
.setEnablePlaceholders(false)
.setInitialLoadSizeHint(INITIAL_LOAD_SIZE_HINT)
.setPageSize(PAGE_SIZE)
.build()
val notificationList = LivePagedListBuilder<Long, Notification>(dataSourceFactory, pagingConfig).build()
Which works fine. However, when my data changes, LiveData<PagedList<Notification>> does not get notified. Is there anything I can do to trigger LiveData refresh (the ViewModel knows when the change occurs).
You can trigger data update using invalidate() method from the DataSource.
When using the Paging Library, it's up to the data layer to notify the other layers of your app when a table or row has become stale. To do so, call invalidate() from the DataSource class that you've chosen for your app.
More information: Notify when data is invalid
According to official documentation: https://developer.android.com/topic/libraries/architecture/paging/data#notify-data-invalid
You have to call dataSourceLiveData.value?.invalidate()
I call it from my view like this:
OnRefresh: View implements SwipeRefreshLayout.OnRefreshListener
override fun onRefresh() {
brewerViewModel.retry()
}
In define the method refresh in my view model:
fun refresh() {
brewerDataSourceFactory.refresh()
}
In my case i'm using retrofit to fetch data from server
ItemResponse is the object which i'm getting from server (Retrofit)
class DataSourceFactory : DataSource.Factory<Int, ItemResponse>() {
lateinit var dataSource: DataSource
var dataSourceLiveData: MutableLiveData<DataSource> =
MutableLiveData<DataSource>()
override fun create(): DataSource<Int, ItemResponse> {
dataSource = DataSource()
dataSourceLiveData.postValue(dataSource)
return dataSource
}
fun refresh() {
dataSourceLiveData.value?.invalidate()
}
}
In my DataSource is defined like following:
class DataSource : PageKeyedDataSource<Int, ItemResponse>
I hope it helps!
Related
I want to update a member variable of an object inside my Repository on a LiveData- Object. The problem is, that if I call the getValue() Method, I keep getting an NullPointerException, although the value does exist inside my Room- Library.
My question now is, how do I get the value from the LiveData Object without calling the observe() Method? (I am not able to call the observe method inside my repository, cause that method wants me to enter a LifeCycleOwner- reference, which is not present inside my repository).
Is there any way to get the value out of the LiveData- object?
My architecture looks like that:
ViewModel --> Repository --> Dao
You need to initialize LiveData object in ViewModel before observing it in Activity/Fragment like this
ProductViewModel.java
public ProductViewModel(DataRepository repository, int productId) {
mObservableProduct = repository.loadProduct(mProductId);
}
public LiveData<ProductEntity> getObservableProduct() {
return mObservableProduct;
}
Here observableProduct is LiveData for observing product details which is initialized in constructor and fetched using getObservableProduct() method
Then you can observe the LiveData in Activity/Fragment like this
MainActivity.java
productViewModel.getObservableProduct().observe(this, new Observer<ProductEntity>() {
#Override
public void onChanged(#Nullable ProductEntity productEntity) {
mProduct = productEntity;
}
});
As you already setup your code architecture like
Flow of LiveData is
DAO -> Repository -> ViewModel -> Fragment
You don't need to observe LiveData in repository because you cannot update UI from there. Observe it from Activity instead and update UI from there.
As you are saying its giving null on getValue(), make sure you are updating db and fetching db from single instance of DAO as per I worked with DAO it will not notify db update of one DAO instance to 2nd DAO instance with LiveData
Also you can observeForever as suggested by #Martin Ohlin, but it will not be lifecycle aware and may lead to crashes. Check your requirement before observing forever
Refer to this for Full LiveData Flow
Refer to this for DAO issues
Edit 1 - Without using LifecycleOwner
You can use void observeForever (Observer<T> observer) (reference) method to observe LiveData without providing any LifecycleOwner as I provided by using this context in above example.
This is how you can observe LiveData without providing any LifecycleOwner and observe the LiveData in repository itself
private void observeForeverProducts() {
mDatabase.productDao().loadAllProducts().observeForever(new Observer<List<ProductEntity>>() {
#Override
public void onChanged(#Nullable List<ProductEntity> productEntities) {
Log.d(TAG, "onChanged: " + productEntities);
}
});
}
But you need to call removeObserver(Observer) explicitly to stop observing the LiveData which was automatically done in previous case with LifecycleOwner. So as per documentation
You should manually call removeObserver(Observer) to stop observing this LiveData. While LiveData has one of such observers, it will be considered as active.
As this doesn't require LifecycleOwner you can call this in Repository without using this parameter as you mentioned which is missing in your repository
In order for the LiveData object works well you need to use the observe method. That is if you want to use the getValue() method and expecting a non-null response you need to use the observe method. Make sure initialize the LiveData object in your ViewModel as #adityakamble49 said in his answer. For initialize the object, you can pass the reference of your LiveData object which was created in your Repository:
ViewModel.java
private LiveData<Client> clientLiveData;
private ClientRepository clientRepo;
public ViewModel(ClientRepository clientRepo) {
this.clientRepo = clientRepo;
clientLiveData = clientRepo.getData();
}
Then you have to observe your ViewModel from the Activity and call the method that you want to update in your ViewModel (or Repo, but remember that Repo conects with the ViewModel and ViewModel with the UI: https://developer.android.com/jetpack/docs/guide ):
Activity.java
viewModel.getClient().observe(this, new Observer<Client>() {
#Override
public void onChanged(#Nullable Client client) {
viewModel.methodWantedInViewModel(client);
}
});
I hope it helps.
I'm not sure exactly what you are trying to accomplish here, but it is possible to observe without a LifeCycleOwner if you use
observeForever instead of observe.
Livedata is used to observe the data streams. In case you want to call the get a list of your entities stored within the Live Data. Something like this can be helpful.
public class PoliciesTabActivity extends AppCompatActivity {
private PolicyManualViewModel mViewModel;
private List<PolicyManual> policyManualList;
#Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_leaves_tab_manager);
mViewModel = ViewModelProviders.of(PoliciesTabActivity.this).get(PolicyManualViewModel.class);
//Show loading screen untill live data onChanged is triggered
policyManualList = new ArrayList<>();
mViewModel.getAllPolicies().observe(this, new Observer<List<PolicyManual>>() {
#Override
public void onChanged(#Nullable List<PolicyManual> sections) {
//Here you got the live data as a List of Entities
policyManualList = sections;
if (policyManualList != null && policyManualList.size() > 0) {
Toast.makeText(PoliciesTabActivity.this, "Total Policy Entity Found : " + policyManualList.size(), Toast.LENGTH_SHORT).show();
} else {
Toast.makeText(PoliciesTabActivity.this, "No Policy Found.", Toast.LENGTH_SHORT).show();
}
}
});
}
}
One more thing - for others with a similar problem - be aware that live data queries will execute only if there is a live observer (i.e. view listening for updates). It won't fill itself just by "laying" there in declarations, like this:
val myLiveData = repository.readSomeLiveData ()
So make sure that you are observing somewhere your LiveData object, either in view or through Transformations.
I am totally confused with one issue Spring data + hibernate
We have a Restful service which we are migrating to V2.
So the old controller looks like
#Api(tags = {"assignments"})
#RestController
#CheckedTransactional
public class AssignmentListController {
#Inject
private AssignmentListService assignmentListService;
//REST function
public list() {....}
}
The REST function list calls AssignmentListService to load assignments, which is a collection, and loads some data lazily. Its works excellent.
What I did is I copied this controller as name AssignmentListControllerV2, and it looks like
#Api(tags = {"assignments"})
#RestController
#CheckedTransactional
public class AssignmentListControllerV2 {
#Inject
private AssignmentListService assignmentListService;
#Inject
private AssignmentDtoMapper assignmentDtoMapper;
public list() {...}
}
The code is same except AssignmentDtoMapper bean added, which is created using MapStruct.
Now the problem, When I call this new service, somehow I get a Lazy Load exception. The error is
could not initialize proxy - no Session
I desperately need some help as I have no clue whats happening. I have just copied the code in a new class and its failing.
The exception is actually pretty clear, Hibernate can't load the lazy fetched member because there is no persistence context open when you hit it.
I suppose that in the V2 the:
#Inject
private AssignmentDtoMapper assignmentDtoMapper;
is to change some JPA business entity into DTO?
It's probably the source of the exception if you try to map not loaded member there.
If you want to avoid the exception on unitiliazed proxy you can try something like
public boolean isProxyInitialized(Object obj){
if(obj instanceof HibernateProxy){
HibernateProxy proxy = (HibernateProxy) obj;
return !proxy.getHibernateLazyInitializer().isUninitialized();
}
return obj != null;
}
It should return true if the member as bean fetched otherwise false.
I am working with Spring 4 and Hazelcast 3.2. I am trying to add a new record to existing cache with below code. somehow cache is not getting updated and at the same time I don't see any errors also. below is the code snippet for reference.
Note:- Cacheable is working fine, only cacheput is not working. Please throw light on this
#SuppressWarnings("unchecked")`enter code here`
#Transactional(readOnly = true, propagation = Propagation.REQUIRED)
#Cacheable(value="user-role-data")
public List<User> getUsersList() {
// Business Logic
List<User> users= criteriaQuery.list();
}
#SuppressWarnings("unchecked")
#Transactional(readOnly = true, propagation = Propagation.SUPPORTS)
#CachePut(value = "user-role-data")
public User addUser(User user) {
return user;
}
I had the same issue and managed to solved it. The issue seemed to be tied to the transaction management.
Bascially updating the cache in the same method where you are creating or updating the new record does not work because the transaction was not committed. Here's how I solved it.
Service layer calls repo to insert user
Then go back to service layer
After the insert /update db call
In the service layer I called a refresh cache method
That returned the user data and this method has the cacheput annotation
After that it worked.
An alternative approach is you could use #CacheEvict(allEntries = true) on the method used to Save or Update or Delete the records. It will flush the existing cache.
Example:
#CacheEvict(allEntries = true)
public void saveOrUpdate(Person person)
{
personRepository.save(person);
}
A new cache will be formed with updated result the next time you call a #Cacheable method
Example:
#Cacheable // caches the result of getAllPersons() method
public List<Person> getAllPersons()
{
return personRepository.findAll();
}
In my application, I need to retrieve the lists of new, updated and removed entities per each transaction. Like this:
// useful functionality
#Transactional
public void createNewBlogPost(int userId, String title, String text) {
Post post = new Post();
post.title = title; // "hello"
post.text = text; // "there"
postRepository.save(post);
// more work with JPA repositories here
}
...
// gets called right after createNewBlogPost()
public void onTransaction(UnitOfWork uow) {
List<?> newEntities = uow.getNewEntities();
assertEquals(1, newEntities.size()); // 1 new entity
Object firstNewEntity = newEntities.get(0);
assertTrue(firstNewEntity instanceof Post); // this new entity
// is a Post
Post newPost = (Post)firstNewEntity;
assertEquals("hello", newPost.title);
assertEquals("there", newPost.text);
}
The most relevant thing I managed to find was an audit functionality that Spring provides with annotations like #CreatedBy, #CreatedDate, #LastModifiedBy, #LastModifiedDate. Though it's technically very close, yet it's not exactly what I want to achieve.
Does Spring Data JPA provide a mechanism to retrieve data changes per every single transaction?
Since your use case is Hibernate and JPA specific, you should take a look at Hibernate Envers and Spring Data Envers. They might give you some ideas, but be careful re: the projects themselves, I'm not sure if they're active.
I've spent some time for the research and managed to find a relatively straightforward Hibernate-specific solution. There are basically 2 problems to resolve:
Intercept data change events.
Do it on a per-request basis.
To address p.1, one can use EventListenerRegistry. Here's an example:
#Component
public class HibernateListenersConfigurer {
#Autowired
private EntityManagerFactory entityManagerFactory;
#Autowired
private HibernateListeners hibernateListeners;
#PostConstruct
public void init() {
HibernateEntityManagerFactory hibernateEntityManagerFactory =
(HibernateEntityManagerFactory)entityManagerFactory;
SessionFactoryImpl sessionFactoryImpl =
(SessionFactoryImpl)hibernateEntityManagerFactory.getSessionFactory();
EventListenerRegistry eventListenerRegistry = sessionFactoryImpl.
getServiceRegistry().
getService(EventListenerRegistry.class);
eventListenerRegistry.appendListeners(EventType.PRE_INSERT, hibernateListeners);
eventListenerRegistry.appendListeners(EventType.PRE_UPDATE, hibernateListeners);
eventListenerRegistry.appendListeners(EventType.PRE_DELETE, hibernateListeners);
}
}
hibernateListeners object gets all these events and can do whatever required to audit them. Here's an example:
#Component
public class HibernateListeners implements
PreInsertEventListener,
PreUpdateEventListener,
PreDeleteEventListener {
#Autowired
private ChangeTracker changeTracker;
#Override
public boolean onPreInsert(PreInsertEvent event) {
// event has a bunch of relevant details
changeTracker.trackChange(event);
return false;
}
...other listeners here...
Then, to address p.2, changeTracker seen above is a request-scoped bean:
#Component
#Scope(value = "request", proxyMode = ScopedProxyMode.TARGET_CLASS)
public class ChangeTracker {
// a sort of "Unit of Work"
private List<Change> changes = new ArrayList<Change>();
public void trackChange(PreInsertEvent event) {
changes.add(makeChangeFromEvent(event));
}
public void handleChanges() {
// Do whatever needed :-)
}
}
Then, there are few options available to finally call handleChanges() once request processing is complete: call it manually, use HandlerInterceptor, use filter, use AOP. HandlerInterceptors and filters, are not as great, because in my case they were getting called after response has already been sent to the client, this caused inconsistency between "business data" and "changes data". I eventually switched to AOP and it seems to work just fine.
Here's a playground: https://github.com/loki2302/spring-change-tracking-experiment
I have a problem implementing forms authentication with an IOC container in my ASP.NET MVC 3 project. We have stored our user information in the database and has a lot of custom properties.
I have an interface of my user definition registrated to the IOC container for development purposes. This interface is given to each controller so the controllers has current user information.
This al works fine until i remove the dummy user registration in the Application_Start
I receive this error:
The current type, ...CurrentUserInformation.IUserInformation, is an interface and cannot be constructed. Are you missing a type mapping?
I don't want to work with a dummy user object because I think this is not the best practice.
Can sombody help me or is there a better way to do this custom authentication?
edit added some code
BaseController
public class BaseController : Controller
{
private readonly IUserInformation _userInformation;
public BaseController(IUserInformation userInformation)
{
_userInformation = userInformation
}
}
Bootstrapper Initialize called from Application_Start
public static void Initialise()
{
var container = BuildUnityContainer();
DependencyResolver.SetResolver(new UnityDependencyResolver(container));
}
private static IUnityContainer BuildUnityContainer()
{
var container = new UnityContainer();
//register all services en repositories
//here i put my dummy user wich i want to remove
container.RegisterInstance<IUserInformation>(
new UserInformation
{
UserId = 1,
...
});
return container;
}
You can use InjectionFactory:
container.RegisterType<IUserInformation, UserInformation>(
// User information is destroyed when the request ends.
// You could use an HttpSessionLifetimeManager as well, if it fits your needs
new HttpRequestLifetimeManager(),
new InjectionFactory(container => {
UserInformation userInfo = // TODO: build your userInformation from custom authentication
return userInfo;
}));