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How to make Room database insert method return int through mvvm architecture?

I want to get the id auto-generated while performing insert operation on Room database. I am implementing MVVM (Model-View-ViewModel) architecture which makes use of DAO to fire queries to Room database. I have added a repository layer between viewmodel and DAO to create an AsyncTask to perform database operations. How do I get the output of insert operation (which is the inserted row's auto-generated id) to the fragment that uses the viewmodel. The layers are as follows: Fragment -> ViewModel -> Repository -> DAO
ListFragment.java
public class ListFragment extends Fragment {
private ReminderViewModel viewModel;
private int id;
...
viewModel = ViewModelProviders.of(this).get(ReminderViewModel.class);
...
id = viewModel.insert(new TodoReminder(0, description, date, time));
...
}
ReminderViewModel.java
public class ReminderViewModel extends AndroidViewModel {
private ReminderRepository repository;
public ReminderViewModel(#NonNull Application application) {
super(application);
repository = new ReminderRepository(application);
}
public int insert(TodoReminder reminder) {
repository.insert(reminder);
}
}
ReminderRepository.java
public class ReminderRepository {
private ReminderDAO reminderDAO;
public ReminderRepository(Application application) {
AppDatabase db = AppDatabase.getDatabase(application);
reminderDAO = db.getReminderDAO();
}
public int insert(TodoReminder reminder) {
new insertAsyncTask(reminderDAO).execute(reminder);
}
private static class InsertAsyncTask extends AsyncTask<TodoReminder, Void, Integer> {
private ReminderDAO asyncTaskDAO;
insertAsyncTask(ReminderDAO dao) {
asyncTaskDAO = dao;
}
#Override
protected Integer doInBackground(final TodoReminder... reminders) {
return asyncTaskDAO.insert(reminders[0]);
}
}
}
ReminderDAO.java
#Dao
public interface ReminderDAO {
#Insert
public int insert(TodoReminder... reminders);
}
ToDoReminder.java
public class TodoReminder implements Serializable {
#PrimaryKey(autoGenerate = true)
#NonNull
private int id;
...
}
How should I get the int returned from the insert method of ReminderDAO and return it from the insert method in ReminderRepository?

You can create your database table in such a way that the id is incremented automatically. In MySQL that is done via the auto_increment keyword. In SQL Server it is done via the identity(1, 1) syntax. In Access it is the autoincrement keyword. In Oracle and PostgreSQL it is done using sequences. If you manage to do this, then you will not need to manually work on incrementing these values. If, for some reason this is out of the question, then you can create a before insert trigger which will load the maximum id and add 1 to it, storing the result in the id. Or, if even that is out of the question, then you can load the last ID, but that has a different syntax in different databases. Or, you can run a query like this:
select max(id) + 1 from yourtable;
but beware possible performance issues and concurrency problems.

I have the exact problem. This is what I did.
I created an interface
public interface Task
{
void processInsert(long id)
}
supply the interface to the insert fcn in the repository
public class Repository {
private Dao myDao;
public void insertMyObject(MyOBject object,Task myInterface ) {
new insertAysncTask(myDao,myInterface).execute(object);
}
private static class insertAsyncTask extends AysncTask<MyObject,Void,Long>{
private Dao mDao;
private Task mTask;
public insertAysncTask(Dao dao, Task task) {
this.mDao = dao;
this.mTask=task;
}
#Override
protected Long doInBackground(MyObject... myObjects) {
return mDao.insertMyObject(myObjects[0]);
}
#Override
protected void onPostExecute(Long aLong) {
super.onPostExecute(aLong);
mTask.processInsert(aLong);
}
}
}
in the DAO class fcn should have return type of Long
public interface MyDao {
#Insert
Long insertMyObject(MyObject object);
have the ViewModel implement the interface
public class MyObjectViewModel extends AndroidViewModel implements Task{
private Repository mRepository;
public MyObjectViewModel(#NonNull Application application) {
super(application);
mRepository = new Repository(application);
}
#Override
public void processInsert(Long id) {
// code for processing the id returned from the db insert
}
public void insertMyObject(MyObject object){
mRepository.insertMyObject(object,this);}
}
in the activity/fragment call the ViewModel insert
mViewModel.insertMyObject(object);
Update
If you want to return the id to the activity or fragment then have the fragment/activity implement the interface instead of the viewmodel
ListFragment extends Fragment implements Task{
.....
#Override
public void processInsert(Long id){
//process id here
}
//call the insert fcn passing in the reference to the fragment
mViewModel.insertMyObject(object,this)
}
Modify the insert fcn in the View Model to accept a reference to the interface
public void insertMyObject(MyObject object, Task myInterface){
mRepository.insertMyObject(object,myInterface);
}
with this approach, the asynctask in the repository insert fcn will hold a reference to the activity/fragment and if the activity/fragment is destroyed before the asynctask finishes this will be a problem. I think it's better to do the processing in the viewmodel if possible. Fragments/activities should only deal with UI concerns not data processing.
Alternative Method
An alternative would be to use a LiveData with an observer.
public class Repository{
private Dao myDao;
private MutableLiveData<Long> dbInsertId = new MutableLiveData<>();
public void insertMyObject(MyObject object){
insertAysnc(object)
}
private void insertAysnc(final MyObject object){
new Thread(new Runnable() {
#Override
public void run() {
Long id=myDao.insertMyObject(object); //call Dao insert fcn
dbInsertId.postValue(id); //set the value of the livedata to the valued returned from the DB insert fcn
}
}).start();
}
public LiveData<Long> getDbInsertedId(){
return dbInsertId;
}
}
In the ViewModel define this fcn
public LiveData<Long> getDbInsertedId(){
return mRepository.getDbInsertedId();// call the repository getId fcn
}
in the onCreate of Activity/Fragment setup an observer on the LiveData
mViewModel= ViewModelProviders.of(this).get(MyViewModel.class);
mViewModel.getDbInsertedId().observe(this, new Observer<Long>() {
#Override
public void onChanged(Long aLong) {
// do something with the long value returned from the database
}
});

JPA persisting does not happen with relation when VARCHARS turn to CLOBs

I do have two entities that relate each other via a OneToMany-Relation.
Entity 1 is named "Change" and looks like the following
public class Change {
String attribute1;
#Column(name="\"ATTRIBUTE1\"")
public void getAttribute1() {
return this.attribute1;
}
public void setAttribute1(String attribute1) {
this.attribute1 = attribute1;
}
// and 7 more of these....
List<ChangeTask> relatedChangeTasks = new ArrayList<ChangeTask>();
#OneToMany(cascade={PERSIST, MERGE, REFRESH}
#JoinTable(name="CHANGE_CHANGETASK", joinColumns={#JoinColumn(name="CHANGE_ID")}, inverseJoinColumns={#JoinColumn(name="CHANGETASK_ID")})
#JoinColumn(name="\"relatedChangeTask_ID\"" )
public List<ChangeTask> getRelatedChangeTasks() {
return this.relatedChangeTasks;
}
public void setRelatedChangeTasks(List<ChangeTask> relatedChangeTasks) {
this.relatedChangeTasks = relatedChangeTasks;
}
}
Entity 2 is named ChangeTask and extends Change.
public class ChangeTask extends Change {
// some additional attributes...
}
Persisting a new or existing Change record with one ChangeTask added to the "relatedChangeTask" list works just perfect.
Now I have to change the annotation of the 8 attributes from Default to #Lob, so Change now looks like this:
public class Change {
String attribute1;
#Lob
#Column(name="\"ATTRIBUTE1\"")
#Basic(fetch=EAGER)
public String getAttribute1() {
if(fieldHandler != null) {
return (java.lang.String) fieldHandler.readObject(this, "attribute1", attribute1);
}
return attribute1;
}
public void setAttribute1(String attribute1) {
if(fieldHandler != null) {
this.attribute1= (java.lang.String) fieldHandler.writeObject(this, "attribute1", this.attribute1, attribute1);
return;
}
this.attribute1= attribute1;
}
// and 7 more of these....
List<ChangeTask> relatedChangeTasks = new ArrayList<ChangeTask>();
#OneToMany(cascade={PERSIST, MERGE, REFRESH}
#JoinTable(name="CHANGE_CHANGETASK", joinColumns={#JoinColumn(name="CHANGE_ID")}, inverseJoinColumns={#JoinColumn(name="CHANGETASK_ID")})
#JoinColumn(name="\"relatedChangeTask_ID\"" )
public List<ChangeTask> getRelatedChangeTasks() {
return this.relatedChangeTasks;
}
public void setRelatedChangeTasks(List<ChangeTask> relatedChangeTasks) {
this.relatedChangeTasks = relatedChangeTasks;
}
}
Now, when I try to add a given ChangeTask to a Change the persist operation does not fail. But at the end of the Transaction the relation has not been persisted, meaning the relation-table "CHANGE_CHANGETASK" remains empty. When I debug through the whole process, I can see that the list contains one entry before "entityManager.merge()" operation and it still contains one entry after the merge. But it never arrives at the database.
Does anybody have an idea what I'm doing wrong here? As strange as it may sound, it must be something related with the #Lob annotations. As soon as I remove those again from the entity everything works fine.
Thanks in advance.

You wrote
public void getAttribute1() {
That can't be right. I think you mean
public String getAttribute1() {
Additionally you have annotated the setter:
#Column(name="\"ATTRIBUTE1\"")
public void setAttribute1(String attribute1) {
this.attribute1 = attribute1;
}
You have to annotage either the field or the getter.

Hibernate/JPA: only one entry can have specific field value

I need something that seems not so specific but anyway I was unable to come up with nice and sophisticated solution.
Say I have very simple hibernate/jpa entity:
#Entity(name="entity")
public class Type {
#Id
#GeneratedValue(strategy=GenerationType.AUTO)
private Long id;
#Column(unique = true, nullable = false)
private String name;
#Column(unique = false, nullable = false)
private boolean defaultType;
}
What i need is to somehow annotate defaultType field so only (and exactly) one persisted entity have this value as true. When new entity get persisted with this defaultType as true, the old one (with defaultType=true) entity has to be altered and its defaultType value changed to false. Also if any entity get changed (its defaultType got changed to true), same rule should apply.
As far I know this can be achieved inside business logic (e.g. in DAO layer), with DB trigger or with hibernates interceptor or event (If there is another way, please let me know). I tried with DAO solution but it's kind of bad solution because it can be bypassed and it is really clumsy for such simple operation. DB triggers can not be added with hibernate/jpa annotations (if I am not mistaken) and i am not sure how to make this functionality with hibernate interceptors/events.
So, what is best solution for this problem?

You need use Callback method in JPA, for example PreUpdate or PostUpdate, for instance:
#Entity
#EntityListeners(com.acme.AlertMonitor.class) // set callback method in another class
public class Account {
Long accountId;
Integer balance;
boolean preferred;
#Id
public Long getAccountId() { ... }
...
public Integer getBalance() { ... }
...
#Transient
public boolean isPreferred() { ... }
...
public void deposit(Integer amount) { ... }
public Integer withdraw(Integer amount) throws NSFException {... }
#PreUpdate // callback method in some class
protected void validateCreate() {
if (getBalance() < MIN_REQUIRED_BALANCE)
throw new AccountException("Insufficient balance to open an
account");
}
#PostUpdate // callback method in some class
protected void adjustPreferredStatus() {
preferred =
(getBalance() >= AccountManager.getPreferredStatusLevel());
}
}
// callback method in another class
public class AlertMonitor {
#PreUpdate // callback method in another class
public void updateAccountAlert(Account acct) {
Alerts.sendMarketingInfo(acct.getAccountId(), acct.getBalance());
}
}
Update: About your question, If I undestand what you want, this code may help you:
#Entity(name="entity")
#EntityListeners(com.yourpackage.TypeListner.class)
public class Type {
...
#Column(unique = false, nullable = false)
private boolean defaultType;
}
public class TypeListner {
pivate static Type objectWithTrue = null;
public void init() { // call this method when application is started
List<Type> results = entityManager
.createQuery("from Type", Type.class)
.getResultList();
for(Type type: results) {
if(type.getDefaultType()) {
objectWithTrue = type;
}
}
}
private void changeDefaultType(Type changed) {
if(changed.getDefaultType()) {
if(changed != objectWithTrue && objectWithTrue != null) {
objectWithTrue.setDefaultType(false);
}
objectWithTrue = changed;
}
}
#PostPresist
public void newType(Type changed) {
changeDefaultType(changed);
}
#PostUpdate
public void updateType(Type changed) {
changeDefaultType(changed);
}
#PreRemove
public void removeType(Type changed) {
if(changed.getDefaultType() && objectWithTrue == changed) {
objectWithTrue = null;
}
}
OR
You can use listner #PreUpdate and #PrePresist and every times overwrite all Type objects without store any variable (it isn't so good for perfomance then first example, but more reliable):
#PreUpdate
void updateType(Type changed) {
if(changed.getDefaultType()
List<Type> results = entityManager
.createQuery("from Type", Type.class)
.getResultList();
for(Type type: results) {
if(changed != type && type.getDefaultType()) {
type.setDefaultType(false);
}
}
}
}

RequestFactoryEditorDriver doesn't save full graph even though "with()" is called. Is circular reference an issue?

Could you guys please help me find where I made a mistake ?
I switched from SimpleBeanEditorDriver to RequestFactoryEditorDriver and my code no longer saves full graph even though with() method is called. But it correctly loads full graph in the constructor.
Could it be caused by circular reference between OrganizationProxy and PersonProxy ? I don't know what else to think :( It worked with SimpleBeanEditorDriver though.
Below is my client code. Let me know if you want me to add sources of proxies to this question (or you can see them here).
public class NewOrderView extends Composite
{
interface Binder extends UiBinder<Widget, NewOrderView> {}
private static Binder uiBinder = GWT.create(Binder.class);
interface Driver extends RequestFactoryEditorDriver<OrganizationProxy, OrganizationEditor> {}
Driver driver = GWT.create(Driver.class);
#UiField
Button save;
#UiField
OrganizationEditor orgEditor;
AdminRequestFactory requestFactory;
AdminRequestFactory.OrderRequestContext requestContext;
OrganizationProxy organization;
public NewOrderView()
{
initWidget(uiBinder.createAndBindUi(this));
requestFactory = createFactory();
requestContext = requestFactory.contextOrder();
driver.initialize(requestFactory, orgEditor);
String[] paths = driver.getPaths();
createFactory().contextOrder().findOrganizationById(1).with(paths).fire(new Receiver<OrganizationProxy>()
{
#Override
public void onSuccess(OrganizationProxy response)
{
if (response == null)
{
organization = requestContext.create(OrganizationProxy.class);
organization.setContactPerson(requestContext.create(PersonProxy.class));
} else
organization = requestContext.edit(response);
driver.edit(organization, requestContext);
}
#Override
public void onFailure(ServerFailure error)
{
createConfirmationDialogBox(error.getMessage()).center();
}
});
}
private static AdminRequestFactory createFactory()
{
AdminRequestFactory factory = GWT.create(AdminRequestFactory.class);
factory.initialize(new SimpleEventBus());
return factory;
}
#UiHandler("save")
void buttonClick(ClickEvent e)
{
e.stopPropagation();
save.setEnabled(false);
try
{
AdminRequestFactory.OrderRequestContext ctx = (AdminRequestFactory.OrderRequestContext) driver.flush();
if (!driver.hasErrors())
{
// Link to each other
PersonProxy contactPerson = organization.getContactPerson();
contactPerson.setOrganization(organization);
String[] paths = driver.getPaths();
ctx.saveOrganization(organization).with(paths).fire(new Receiver<Void>()
{
#Override
public void onSuccess(Void arg0)
{
createConfirmationDialogBox("Saved!").center();
}
#Override
public void onFailure(ServerFailure error)
{
createConfirmationDialogBox(error.getMessage()).center();
}
});
}
} finally
{
save.setEnabled(true);
}
}
}

with() is only used for retrieval of information, so your with() use with a void return type is useless (but harmless).
Whether a full graph is persisted is entirely up to your server-side code, which is intimately bound to your persistence API (JPA, JDO, etc.)
First, check that the Organization object you receive in your save() method on the server-side is correctly populated. If it's not the case, check your Locators (and/or static findXxx methods) ; otherwise, check your save() method's code.
Judging from the code above, I can't see a reason why it wouldn't work.

It took me some time to realize that the problem was the composite id of Person entity.
Below is the code snippet of PojoLocator that is used by my proxy entities.
public class PojoLocator extends Locator<DatastoreObject, Long>
{
#Override
public DatastoreObject find(Class<? extends DatastoreObject> clazz, Long id)
{
}
#Override
public Long getId(DatastoreObject domainObject)
{
}
}
In order to fetch child entity from DataStore you need to have id of a parent class. In order to achieve that I switched "ID class" for Locator<> to String which represents textual form of Objectify's Key<> class.
Here is how to looks now:
public class PojoLocator extends Locator<DatastoreObject, String>
{
#Override
public DatastoreObject find(Class<? extends DatastoreObject> clazz, String id)
{
Key<DatastoreObject> key = Key.create(id);
return ofy.load(key);
}
#Override
public String getId(DatastoreObject domainObject)
{
if (domainObject.getId() != null)
{
Key<DatastoreObject> key = ofy.fact().getKey(domainObject);
return key.getString();
} else
return null;
}
}
Please note that your implementation may slightly differ because I'm using Objectify4.

PreUpdate not firing when adding to a collection [duplicate]

This question already has answers here:
JPA EventListener method not called on change to many-to-many collection?
(2 answers)
Closed 3 years ago.
I have a JPA annotated class which contains a collection like so:
#Entity
public class Employee {
#Id
private int id;
#Basic
private String name;
#OneToMany
#JoinTable(name = "ORG", joinColumns = #JoinColumn(name="MINION"),
inverseJoinColumns = #JoinColumn(name="EMP"))
private List<Employee> minions = new ArrayList<Employee>();
#PreUpdate
public void preUpdate(){ ... }
}
What I'm seeing is that if I have a managed Employee entity and I add to it's collection of minions the preUpdate method is not getting invoked. A new row is added to the mapping table in the DB so I know the update is going through. If I change a property directly on the Employee, like name, then preUpdate fires as expected when the transaction is committed.
Is there a way to get PreUpdate to fire when a mapped collection is modified? Or is there some other technique or Hibernate specific annotation for detecting when this happens?

#PreUpdate event is triggered just before database UPDATE operation is executed for the entity in question.
If you're not updating direct properties of Employee, there's no UPDATE to execute for its table and thus #PreUpdate listener is never called. You should have better luck using #PrePersist event which is triggered by "flush" rather than "update".

Maybe a this custom workaround works:
Create a subclass of ArrayList which identifies changes through ActionListener pattern
public class Employee {
....
private List<Employee> minions = createChangeNotifierList();
private List<Employee> createChangeNotifierList() {
ChangeNotifierList<Employee> l = new ChangeNotifierList<Employee>();
l.setActionListener(new ActionListener() {
public void actionPerformed(ActionEvent e) {
preUpdate();
}
});
return l;
}
public void setMinions(List<Employee> l) {
if (!(l instanceof ChangeNotifierList)) {
l = createChangeNotifierList();
preUpdate();
}
this.minions = l;
}
public void preUpdate(){ ... }
}
public class ChangeNotifierList<T> extends ArrayList<T> {
private ActionListener actionListener;
public ChangeNotifierList() {
}
public ChangeNotifierList(List<T> list) {
super.addAll(list);
}
public void setActionListener(ActionListener actionListener) {
this.actionListener = actionListener;
}
public boolean add(T e) {
boolean b = super.add(e);
if (b) {
notifyChange();
}
return b;
}
private void notifyChange() {
actionListener.actionPerformed(null);
}
.....
}

Here is my implementation for Hibernate provider:
http://pastebin.com/8cPB96bZ
Generally you just mark methods that should be called in the case of a dirty collection with #PreCollectionChange annotation.