Jetpack Compose: Modify Room data class using TextField - android

Modifying simple values and data classes using EditText is fairly straight forward, and generally looks like this:
data class Person(var firstName: String, var lastName: Int)
// ...
val (person, setPerson) = remember { mutableStateOf(Person()) }
// common `onChange` function handles both class properties, ensuring maximum code re-use
fun <T> onChange(field: KMutableProperty1<Person, T>, value: T) {
val nextPerson = person.copy()
field.set(nextPerson, value)
setPerson(nextPerson)
}
// text field for first name
TextField(
value = person.firstName,
onChange = { it -> onChange(Person::firstName, it) })
// text field for last name name
TextField(
value = person.lastName,
onChange = { it -> onChange(Person::lastName, it) })
As you can see, the code in this example is highly reusable: thanks to Kotlin's reflection features, we can use a single onChange function to modify every property in this class.
However, a problem arises when the Person class is not instantiated from scratch, but rather pulled from disk via Room. For example, a PersonDao might contain a `findOne() function like so:
#Query("SELECT * FROM peopleTable WHERE id=:personId LIMIT 1")
fun findOne(personId: String): LiveData<Person>
However, you cannot really use this LiveData in a remember {} for many reasons:
While LiveData has a function called observeAsState(), it returns State<T> and not MutableState<T>, meaning that you cannot modify it with the TextFields. As such this does not work:
remember { personFromDb.observeAsState()}
You cannot .copy() the Person that you get from your database because your component will render before the Room query is returned, meaning that you cannot do this, because the Person class instance will be remembered as null:
remember { mutableStateOf(findPersonQueryResult.value) }
Given that, what is the proper way to handle this? Should the component that contains the TextFields be wrapped in another component that handles the Room query, and only displays the form when the query is returned? What would that look like with this case of LiveData<Person>?


I would do it with a copy and an immutable data class
typealias PersonID = Long?
#Entity
data class Person(val firstName: String, val lastName: String) {
#PrimaryKey(autoGenerate = true)
val personID: PersonID = null
}
//VM or sth
object VM {
val liveData: LiveData<Person> = MutableLiveData() // your db call
val personDao: PersonDao? = null // Pretending it exists
}
#Dao
abstract class PersonDao {
abstract fun upsert(person: Person)
}
#Composable
fun test() {
val personState = VM.liveData.observeAsState(Person("", ""))
TextField(
value = personState.value.firstName,
onValueChange = { fName -> VM.personDao?.upsert(personState.value.copy(firstName = fName))}
)
}

Related

How to create Entity and data classes by ROOM in android

How to create Entity and data classes by ROOM in android?
I have JSON structure:
data class ListResponse(val item: ListItem)
data class ListItem(
#SerializedName("id")
val id: List<CheckUnCheckItem>
)
data class CheckUnCheckItem(
#SerializedName("check")
val check: CheckItem,
#SerializedName("unCheck")
val UnCheck: UnCheckItem
)
data class CheckItem(
#SerializedName("url")
val url: String,
#SerializedName("text")
val text: String,
#SerializedName("color")
val color: String
)
data class UnCheckItem(
#SerializedName("url")
val urlUnCheck: String,
#SerializedName("text")
val textUnCheck: String,
#SerializedName("color")
val colorUnCheck: String
)
But How can I create such ROOM Entity?
Do I need to use #TypeConverter?
#Entity(tableName = TABLE_NAME)
data class ListEntity(
#PrimaryKey #SerializedName("id")
val id: CheckUnCheckItem,
#SerializedName("check")
val check: CheckItem,
#SerializedName("unCheck")
val unCheck: UnCheckItem,
#SerializedName("url")
val url: String,
#SerializedName("text")
val text: String,
#SerializedName("size")
val size: String
){
companion object{
const val TABLE_NAME = "db_table"
}
class RoomTypeConverters{
#TypeConverter
fun convertCheckItemListToJSONString(checkList: CheckItem): String = Gson().toJson(checkList)
#TypeConverter
fun convertJSONStringToCheckItemList(jsonString: String): CheckItem = Gson().fromJson(jsonString,CheckItem::class.java)
}
}
is my data and entity classes are correct?
Do I need class witch extends RoomDatabase?
Or better I need to separate db and create for check and uncheck another db?

Or better I need to separate db and create for check and uncheck another db?
As database implies it is able to store data not just one but many. As such a single database is all that would be required. SQLite is a relational database and is designed to store related data. Related data is typically stored in multiple tables. So again a single database will very likely be sufficient.
Do I need to use #TypeConverter?
You never actually need Type Converters. However, for any Object, other than those directly handled (e.g. String, Int, Long, Double, Float, ByteArray) then you either need to break these down into such handled objects or have a types converter that will convert the object to and from such an object.
For example, based upon your #Entity annotated ListEntity class then:-
field id would need a TypeConverter as the type CheckUnCheckItem is not an object type that can be directly handled by Room. So you would need two TypeConverters that could convert from a CheckUncheckItem to and from a type that can be handled by Room.
fields check and uncheck would need two TypeConverters (and it looks as though the Type Converters you have coded will handle the conversion).
fields url,text and size, as they are all String types do not need Type Converters as Room handles strings.
Room has to know about the Type Converters. So you need an #TypeConverters annotation. It's placement defines the scope. Using the annotation to preced the #Database annotation has the most far reaching scope.
Do I need class witch extends RoomDatabase?
Yes. However it has to be an abstract class and should have an abstract function to retrieve an instance of each #Dao annotated interface (or abstract class, in which case the functions have to be abstract, there is no need for an abstract class with Kotlin as functions in an interface can have bodies)).
This class should be annotated with the #Database annotation, the entities parameter of the annotation should include the list of classes for each each table (#Entity annotated class). e.g.
#TypeConverters(value = [ListEntity.RoomTypeConverters::class])
#Database(entities = [ListEntity::class], exportSchema = false, version = 1)
abstract class TheDatabase: RoomDatabase(){
}
However, using the above along with your classes results in a build error as per:-
ListEntity.java:11: error: Cannot figure out how to save this field into database. You can consider adding a type converter for it. private final a.a.so74708202kotlinroomentitydesign.CheckUnCheckItem id = null;
as explained CheckUnCheckItem cannot be handled by Room.
Amending the RoomTypeConverters class to be:-
class RoomTypeConverters{
#TypeConverter
fun convertItemListToJSONString(invoiceList: Item): String = Gson().toJson(invoiceList)
#TypeConverter
fun convertJSONStringToItemList(jsonString: String): Item = Gson().fromJson(jsonString,Item::class.java)
#TypeConverter
fun convertCheckUnCheckItemToJSONString(cuc: CheckUnCheckItem): String = Gson().toJson(cuc)
#TypeConverter
fun convertJSONStringToCheckUnCheckItem(jsonString: String): CheckUnCheckItem = Gson().fromJson(jsonString,CheckUnCheckItem::class.java)
}
Resolves the build issue and in theory you have a potentially usable database.
However, you obviously need code to access the database. As such you would very likely want to have. as previously mentioned, an #Dao annotated interface e.g
#Dao
interface TheDAOs {
#Insert
fun insert(listEntity: ListEntity): Long
#Query("SELECT * FROM ${TABLE_NAME}")
fun getAll(): List<ListEntity>
}
This will suffice to allow rows to be inserted into the database and for all the rows to be extracted from the database into a List<ListEntity).
From the built database you need to get an instance of the TheDAOs and thus the #Database annotated class could then be
:-
#TypeConverters(value = [ListEntity.RoomTypeConverters::class])
#Database(entities = [ListEntity::class], exportSchema = false, version = 1)
abstract class TheDatabase: RoomDatabase(){
abstract fun getTheDAOsInstance(): TheDAOs
}
To demonstrate actual use of the above then consider the following code in an activity:-
class MainActivity : AppCompatActivity() {
lateinit var roomDBInstance: TheDatabase
lateinit var theDAOs: TheDAOs
override fun onCreate(savedInstanceState: Bundle?) {
super.onCreate(savedInstanceState)
setContentView(R.layout.activity_main)
roomDBInstance = Room.databaseBuilder(this,TheDatabase::class.java,"The_database_name.db")
.allowMainThreadQueries() /* NOTE ADDED FOR CONVENIENCE AND BREVITY */
.build()
/* Note the database itself does not yet exist, it's creation is delayed until an attempt is made to access it. So:- */
theDAOs = roomDBInstance.getTheDAOsInstance() /* Still the database is not created/accessed */
showData(theDAOs.getAll()) /* No data has been added BUT the database will now exist */
theDAOs.insert(
ListEntity(
id = CheckUnCheckItem(
check = Item (
url ="URL001",
text = "TEXT001",
color = "RED"
),
unCheck = Item(
url ="URL002",
text = "TEXT002",
color = "BLUE"
)
),
check = Item(url = "URL003", text ="TEXT003", color ="WHITE"),
unCheck = Item(url = "URL004", text = "TEXT004", color = "BLACK"),
url = "URL005", text = "TEXT005", size = "BIG"
)
)
showData(theDAOs.getAll())
}
fun showData(listEntities: List<ListEntity>) {
for (li in listEntities) {
Log.d(
"DBINFO",
"id is $li.id.check.url${li.id.check.text}.... " +
"\n\tcheck is ${li.check.url} .... " +
"\n\tuncheck is ${li.unCheck.url} ...." +
"\n\turl is ${li.url} text is ${li.text} size is ${li.size}"
)
}
}
}
The output to the log being:-
D/DBINFO: id is ListEntity(id=CheckUnCheckItem(check=Item(url=URL001, text=TEXT001, color=RED), unCheck=Item(url=URL002, text=TEXT002, color=BLUE)), check=Item(url=URL003, text=TEXT003, color=WHITE), unCheck=Item(url=URL004, text=TEXT004, color=BLACK), url=URL005, text=TEXT005, size=BIG).id.check.urlTEXT001....
check is URL003 ....
uncheck is URL004 ....
url is URL005 text is TEXT005 size is BIG
The Database via App Inspection being"-
So finally
is my data and entity classes are correct?
From a database aspect yes, they work after a few amendments. However, I suspect that your classes are probably not what you intended.
An Alternative Approach
If this were to be approached from a database perspective and normalised and without bloat and without the need for type converters then consider the following:-
The embedded Item's (uncheck and check) are basically repetition, so could probably be a table (related to the db_table). Hence 2 tables. One for the ListEntity (Alternative) and another for the Items (AlternativeItem) so the 2 #Entity annotated classes could be:-
/* Alternative Approach */
#Entity(
/* Foreign Keys NOT REQUIRED, they enforce Referential Integrity */
foreignKeys = [
ForeignKey(
entity = AlternativeItem::class,
parentColumns = ["alternativeItemId"],
childColumns = ["unCheckIdMap"]
/* OPTIONAL within a Foreign Key, they help automatically maintain Referential Integrity*/,
onDelete = ForeignKey.CASCADE,
onUpdate = ForeignKey.CASCADE
),
ForeignKey(
entity = AlternativeItem::class,
parentColumns = ["alternativeItemId"],
childColumns = ["checkIdMap"],
onDelete = ForeignKey.CASCADE,
onUpdate = ForeignKey.CASCADE
)
]
)
data class Alternative(
#PrimaryKey
val id: Long?=null,
#ColumnInfo(index = true)
val unCheckIdMap: Long, /* map to the id of the related Item (AlternativeItem) for the uncheck */
#ColumnInfo(index = true)
val checkIdMap: Long, /* map to the id of the related Item (AlternativeItem) for the uncheck */
val url: String,
val text: String,
val size: String
)
#Entity
data class AlternativeItem(
#PrimaryKey
val alternativeItemId: Long?=null,
val alternativeItemUrl: String,
val alternativeItemText: String,
val alternativeItemColor: String
)
As you would typically want the Alternative along with it's related AlternativeItems then a POJO that caters for the togetherness :-
data class AlternativeWithUncheckAndCheck(
#Embedded
val alternative: Alternative,
#Relation(entity = AlternativeItem::class, parentColumn = "unCheckIdMap", entityColumn = "alternativeItemId")
val unCheck: AlternativeItem,
#Relation(entity = AlternativeItem::class, parentColumn = "checkIdMap", entityColumn = "alternativeItemId")
val check: AlternativeItem
)
There would be a need for some extra functions in the #Dao annotated interface, so :-
#Insert
fun insert(alternative: Alternative): Long
#Insert
fun insert(alternativeItem: AlternativeItem): Long
#Transaction
#Query("")
fun insertAlternativeAndUncheckAndCheck(alternative: Alternative, uncheck: AlternativeItem, check: AlternativeItem): Long {
var uncheckId = insert(uncheck)
var checkId = insert(check)
return insert(Alternative(null,url = alternative.url, text = alternative.text, size = alternative.size, unCheckIdMap = uncheckId, checkIdMap = checkId ))
}
#Transaction
#Query("SELECT * FROM alternative")
fun getAllAlternativesWithRelatedUnCheckAndCheck(): List<AlternativeWithUncheckAndCheck>
note that the insertAlternativeAndUncheckAndCheck does what it says (note that it is overly simple and could need some enhancements to expand upon the principle)
To demonstrate this, all that is then required is to add the new entities to the entities parameter and to then add some code to the activity.
The amended #Database annotation:-
#Database(entities = [ListEntity::class, /* for the alternative approach */ Alternative::class, AlternativeItem::class], exportSchema = false, version = 1)
The activity code (that caters for both approaches in a similar/equivalanet way of storing and retrieving the data) :-
class MainActivity : AppCompatActivity() {
lateinit var roomDBInstance: TheDatabase
lateinit var theDAOs: TheDAOs
override fun onCreate(savedInstanceState: Bundle?) {
super.onCreate(savedInstanceState)
setContentView(R.layout.activity_main)
roomDBInstance = Room.databaseBuilder(this,TheDatabase::class.java,"The_database_name.db")
.allowMainThreadQueries() /* NOTE ADDED FOR CONVENIENCE AND BREVITY */
.build()
/* Note the database itself does not yet exist, it's creation is delayed until an attempt is made to access it. So:- */
theDAOs = roomDBInstance.getTheDAOsInstance() /* Still the database is not created/accessed */
showData(theDAOs.getAll()) /* No data has been added BUT the database will now exist */
theDAOs.insert(
ListEntity(
id = CheckUnCheckItem(
check = Item (
url ="URL001",
text = "TEXT001",
color = "RED"
),
unCheck = Item(
url ="URL002",
text = "TEXT002",
color = "BLUE"
)
),
check = Item(url = "URL003", text ="TEXT003", color ="WHITE"),
unCheck = Item(url = "URL004", text = "TEXT004", color = "BLACK"),
url = "URL005", text = "TEXT005", size = "BIG"
)
)
showData(theDAOs.getAll())
/* Alternative equivalent */
theDAOs.insertAlternativeAndUncheckAndCheck(
Alternative(url = "URL005", size = "BIG", text = "TEXT005", checkIdMap = -1, unCheckIdMap = -1),
check = AlternativeItem(alternativeItemUrl = "URL001", alternativeItemText = "TEXT001", alternativeItemColor = "RED"),
uncheck = AlternativeItem(alternativeItemUrl = "URL002", alternativeItemText = "TEXT002", alternativeItemColor = "BLUE" )
)
showAlternativeData(theDAOs.getAllAlternativesWithRelatedUnCheckAndCheck())
}
fun showData(listEntities: List<ListEntity>) {
for (li in listEntities) {
Log.d(
"DBINFO",
"id is $li.id.check.url${li.id.check.text}.... " +
"\n\tcheck is ${li.check.url} .... " +
"\n\tuncheck is ${li.unCheck.url} ...." +
"\n\turl is ${li.url} text is ${li.text} size is ${li.size}"
)
}
}
fun showAlternativeData(listAlternatives: List<AlternativeWithUncheckAndCheck>) {
for (la in listAlternatives) {
Log.d("DBALTINFO",
"id is ${la.alternative.id} URL is ${la.alternative.url} TEXT is ${la.alternative.text} SIZE is ${la.alternative.size} " +
"\n\t UNCHECK id is ${la.unCheck.alternativeItemId} url is ${la.unCheck.alternativeItemUrl} text is ${la.unCheck.alternativeItemText} color is ${la.unCheck.alternativeItemColor}" +
"\n\t CHECK id is ${la.check.alternativeItemId} url is ${la.check.alternativeItemUrl} text is ${la.check.alternativeItemText} color is ${la.check.alternativeItemColor}")
}
}
}
Note that the Alternative code is probably more along the lines of what you probably want according to the interpretation of the shown JSON.
When run then the result is now:-
D/DBINFO: id is ListEntity(id=CheckUnCheckItem(check=Item(url=URL001, text=TEXT001, color=RED), unCheck=Item(url=URL002, text=TEXT002, color=BLUE)), check=Item(url=URL003, text=TEXT003, color=WHITE), unCheck=Item(url=URL004, text=TEXT004, color=BLACK), url=URL005, text=TEXT005, size=BIG).id.check.urlTEXT001....
check is URL003 ....
uncheck is URL004 ....
url is URL005 text is TEXT005 size is BIG
D/DBALTINFO: id is 1 URL is URL005 TEXT is TEXT005 SIZE is BIG
UNCHECK id is 1 url is URL002 text is TEXT002 color is BLUE
CHECK id is 2 url is URL001 text is TEXT001 color is RED
it is suspected that BLACK/WHITE or RED/BLUE is superfluous in your interpretationof the JSON to data classes (and hence excluded in the alternative).
The database, via App Inspection (in regards to the alternative approach) is:-
and :-
i.e. only the actual data is store the BLOAT (field/type descriptions, separators, enclosing data) is not stored thus
the database will hold more data in less space.
the handling of the data will thus be more efficient (e.g. a buffer can hold more actual data instead of BLOAT).
querying the data such as for example searching for all BLUE's is directly a search for that, whilst with converted data you may have issues distinguishing between BLOAT and actual data
However, the negative, is that more code and thought is required.
Note this answer is intended to deal with the basic principles and is most certainly not fully comprehensive.

JetPack Compose + Room + LiveData + ViewModel

In a Jetpack Compose component I'm subscribing to Room LiveData object using observeAsState.
The initial composition goes fine, data is received from ViewModel/LiveData/Room.
val settings by viewModel.settings.observeAsState(initial = AppSettings()) // Works fine the first time
A second composition is initiated, where settings - A non nullable variable is set to null, and the app crashed with an NPE.
DAO:
#Query("select * from settings order by id desc limit 1")
fun getSettings(): LiveData<AppSettings>
Repository:
fun getSettings(): LiveData<AppSettings> {
return dao.getSettings()
}
ViewModel:
#HiltViewModel
class SomeViewModel #Inject constructor(
private val repository: AppRepository
) : ViewModel() {
val settings = repository.getSettings()
}
Compose:
#OptIn(ExperimentalFoundationApi::class)
#Composable
fun ItemsListScreen(viewModel: AppViewModel = hiltViewModel()) {
val settings by viewModel.settings.observeAsState(initial = AppSettings())
Edit:
Just to clearify, the DB data does not change. the first time settings is fetched within the composable, a valid instance is returned.
Then the component goes into recomposition, when ItemsListScreen is invoked for the second time, then settings is null (the variable in ItemsListScreen).

Once the LiveData<Appsettings> is subscribed to will have a default value of null. So you get the default value required by a State<T> object, when you call LiveData<T>::observeAsState, followed by the default LiveData<T> value, this being null
LiveData<T> is a Java class that allows nullable objects. If your room database doesn't have AppSettings it will set it a null object on the LiveData<AppSettings> instance. As Room is also a Java library and not aware of kotlin language semantics.
Simply put this is an interop issue.
You should use LiveData<AppSettings?> in kotlin code and handle null objects, or use some sort of MediatorLiveData<T> that can filter null values for example some extensions functions like :
#Composable
fun <T> LiveData<T?>.observeAsNonNullState(initial : T & Any, default : T & Any) : State<T> =
MediatorLiveData<T>().apply {
addSource(this) { t -> value = t ?: default }
}.observeAsState(initial = initial)
#Composable
fun <T> LiveData<T?>.observeAsNonNullState(initial : T & Any) : State<T> =
MediatorLiveData<T>().apply {
addSource(this) { t -> t?.run { value = this } }
}.observeAsState(initial = initial)

If you only need to fetch settings when viewModel is initialised, you can try putting it in an init block inside your ViewModel.

Loop-ing mutiple values with the use of 1 instance from a data class

I am trying to figure out how to loop a data class. I have a function called getAges() which contains a listof Ages from 1 - 10. Each age are called from a data class called Age, which should be an Int. How can I successfully loop through Age with different numbers, for ex 1-10? Appreciate the feedback!
My Data class:
#Entity(tableName = "dropdown_age")
data class Age(
#PrimaryKey(autoGenerate = true)
#ColumnInfo(name = "age")
val age: Int?
)
My Function called getAges:
class ProfileViewModel: Viewmodel() {
fun getAges() = listOf(
Age(1), Age(2), Age(3), Age(4), Age(5),
Age(6), Age(7), Age(8), Age(9), Age(10),
)
}

There is a List "constructor" function that can be used to create a List using a lambda where the lambda parameter is an index, starting at 0. (I use quotation marks for constructor because interfaces don't have true constructors. This is just a function that looks like a constructor because of how it is capitalized.)
fun getAges() = List(10) { Age(it + 1) }
Or you can use the map function with a range. map modifies each item out of any Iterable to produce a new List.
fun getAges() = (1..10).map { Age(it) }
// or
fun getAges() = (1..10).map(::Age)

Using collections api forEach
getAges().forEach{
println(it.age)
}
Or using normal For loop
for (age: Age in getAges()) {
println(age.age)
}

How to programically trigger notify on MutableLiveData change

I have a LiveData property for login form state like this
private val _authFormState = MutableLiveData<AuthFormState>(AuthFormState())
val authFormState: LiveData<AuthFormState>
get() =_authFormState
The AuthFormState data class has child data objects for each field
data class AuthFormState (
var email: FieldState = FieldState(),
var password: FieldState = FieldState()
)
and the FieldState class looks like so
data class FieldState(
var error: Int? = null,
var isValid: Boolean = false
)
When user types in some value into a field the respective FieldState object gets updated and assigned to the parent AuthFormState object
fun validateEmail(text: String) {
_authFormState.value!!.email = //validation result
}
The problem is that the authFormState observer is not notified in this case.
Is it possible to trigger the notification programically?

Maybe you can do:
fun validateEmail(text: String) {
val newO = _authFormState.value!!
newO.email = //validation result
_authFormState.setValue(newO)
}

You have to set the value to itself, like this: _authFormState.value = _authFormState.value to trigger the refresh. You could write an extension method to make this cleaner:
fun <T> MutableLiveData<T>.notifyValueModified() {
value = value
}
For such a simple data class, I would recommend immutability to avoid issues like this altogether (replaces all those vars with vals). Replace validateEmail() with something like this:
fun validateEmail(email: String) = //some modified version of email
When validating fields, you can construct a new data object and set it to the live data.
fun validateFields() = _authFormState.value?.let {
_authFormState.value = AuthFormState(
validateEmail(it.email),
validatePassword(it.password)
)
}

How to get a specific Entity in Room

So, I'm using Room database to store courses and I'm stuck on the method that returns the course with the name(course) that I want because it's always returning null. I have diminished my database to have 2 courses with the course variable as:
As you can see in the picture above, when I try to get the CourseEnt in the Repository with course = fun, which I can see below that it exists, it returns a LiveData with a null value instead of the CourseEnt that I wanted.
Any idea on what I'm doing wrong or on what should I look into with debugger?
Here's the code:
Entity:
#Entity(tableName = "courses_table")
data class CoursesEnt (#PrimaryKey val course: String,
val location: String,
val description: String,
val difficulty: Double,
val distance: Double,
val photos: ListInt,
val category: String,
val activities: ListString)//ListString is a type converter that converts a String into a List<String> and vice-versa
DAO:
#Dao
interface CoursesDao {
#Query("SELECT * from courses_table ORDER BY course ASC")
fun getAllCourses(): LiveData<List<CoursesEnt>>
#Query("SELECT * FROM courses_table WHERE course LIKE :str")
fun getCourse(str: String):LiveData<CoursesEnt>
...
}
Repository:
class CoursesRepository(private val coursesDao: CoursesDao){
val allCourses: LiveData<List<CoursesEnt>> = coursesDao.getAllCourses()
var singleCourse: LiveData<CoursesEnt> = coursesDao.getCourse("")
#WorkerThread
fun getCourse(str: String) {
singleCourse = coursesDao.getCourse(str)
}
...
}

Read documentation, liveData will always return null for straight call, you have to observe LiveData, the result value from Room will be in block. This is some example of usage
mViewModel.getAllUsers().observe( this#YourActivity, Observer {
// it - is all users from DB
})
but if you will call
val users = mViewModel.getAllUsers()
the result will be null

Categories

Resources