Kotlin Room Database Save Control - android

I save data to Room database with a button. However, every time I press the button, that item is registered and listed again and again. I want to write a control. I do not want it to save it if it is registered. I will be glad if you help.
ArticleDao
#Dao
interface ArticleDao {
#Insert(onConflict = OnConflictStrategy.REPLACE)
suspend fun upsert(article: Article): Long
NewsRepisotry
class NewsRepository(
val db: ArticleDatabase
) {
suspend fun upsert(article: Article)=db.getArticleDao().upsert(article)
fun getSavedNews()=db.getArticleDao().getAllArticles()
ArticleDatabase
#Database(
entities = [Article::class],
version = 1
)
#TypeConverters(Converters::class)
abstract class ArticleDatabase : RoomDatabase() {
abstract fun getArticleDao(): ArticleDao
companion object {
#Volatile
private var instance: ArticleDatabase? = null
private val LOCK = Any()
operator fun invoke(context: Context) = instance ?: synchronized(LOCK) {
instance ?: createDatabase(context).also { instance = it }
}
private fun createDatabase(context: Context) =
Room.databaseBuilder(
context.applicationContext,
ArticleDatabase::class.java,
"article_db.db"
).build()
}
}
Article.kt
#Entity(
tableName = "articles"
)
data class Article(
#PrimaryKey(autoGenerate = true)
var Id: Int? = null,
val author: String?,
val content: String?,
val description: String?,
val publishedAt: String?,
val source: Source?,
val title: String?,
val url: String?,
val urlToImage: String?
) : Serializable

Your issue would appear to be that #Insert(onConflict = OnConflictStrategy.REPLACE) is inserting instead of replacing.
The OnConflict strategy will only be actioned if there is a conflict. That is typically that a UNIQUE constraint is violated (see link below for other violations covered).
From your explanation of the issue there is no violation and thus instead of the row(s) being replaced, they are instead inserted.
You may wish to refere to https://sqlite.org/lang_conflict.html
In short you need a UNIQUE index to cover your scenario to ensure that a violation occurs.
Without the Article class it is impossible to say what actual change is required. However the following example shows 2 classes (entities) and how a unique index can be added to a column/property articleName.
So first a guess as what your Article class could be:-
#Entity
data class Article(
#PrimaryKey
var articelId: Long? = null,
var articleName: String,
var otherData: String
)
and here an equivalent with a UNIQUE index on the articleName property/column :-
#Entity(indices = [Index(value = ["articleName"],unique = true)])
data class ArticleV2(
#PrimaryKey
var articleId: Long? = null,
var articleName: String,
var otherData: String
)
Example/Demo
As an example of how both work differently, the latter according to your expectations, consider the following code, utilising the above, (for brevity/convenience run on the main thread) :-
The #Dao ArticleDao for both tables/entiities/classes :-
#Dao
interface ArticleDao {
#Insert(onConflict = OnConflictStrategy.REPLACE)
fun upsert(article: Article): Long
#Insert(onConflict = OnConflictStrategy.REPLACE)
fun upsert(articleV2: ArticleV2)
#Query("SELECT count(*) FROM article")
fun getArticleCount(): Long
#Query("SELECT count(*) FROM articlev2")
fun getArticleV2Count(): Long
}
The #Database ArticleDatabase class :-
#Database(
entities = [Article::class, ArticleV2::class],
version = 1
)
abstract class ArticleDatabase : RoomDatabase() {
abstract fun getArticleDao(): ArticleDao
companion object {
#Volatile
private var instance: ArticleDatabase? = null
private val LOCK = Any()
operator fun invoke(context: Context) = instance ?: synchronized(LOCK) {
instance ?: createDatabase(context).also { instance = it }
}
private fun createDatabase(context: Context) =
Room.databaseBuilder(
context.applicationContext,
ArticleDatabase::class.java,
"article_db.db"
)
.allowMainThreadQueries()
.build()
}
}
Finally an activity, that replicates your "every time I press the button" by looping 5 times inserting one row into each table per iteration and then after the loop writing the number of rows in each of the tables to the log.
class MainActivity : AppCompatActivity() {
lateinit var db: ArticleDatabase
lateinit var dao: ArticleDao
override fun onCreate(savedInstanceState: Bundle?) {
super.onCreate(savedInstanceState)
setContentView(R.layout.activity_main)
db = ArticleDatabase.invoke(this)
dao = db.getArticleDao()
for(i in 1..5) {
dao.upsert(Article(null, "Article", "otherdata$i"))
dao.upsert(ArticleV2(null,"Article","otherdata$i"))
}
Log.d("ARTICLECOUNT","Number of Articles in article table = " + dao.getArticleCount() + "... in articleV2 table = " + dao.getArticleV2Count())
}
}
When run (first time) the output in the log contains:-
D/ARTICLECOUNT: Number of Articles in article table = 5... in articleV2 table = 1
So 5 rows inserted into the article table but only 1 row in the articleV2 table (as the value used for the articleName is the same).
After running Database Inspector shows :-
The article table
The articleV2 table
As can be seen the otherData column has been replaced throughout and is otherdata5
If the OnConflict strategy were IGNORE then otherData would have a value of otherdata1
Additional
regarding the comment and Article class now added.
First of all, thank you sir. I have also added the Article class. Your explanation is very good, but I could not understand exactly what I needed to change.
You need to decide what constitutes a duplicate entry.
Perhaps the URL if unchanged could be the most likely to indicate a duplicate.
So you could use :-
#Entity( tableName = "articles", indices = [Index(value = ["url"],unique = true)] ) //<<<<<<<<< ONLY CHANGE IS THE #Entity
data class Article(
#PrimaryKey(autoGenerate = true)
var Id: Int? = null,
val author: String?,
val content: String?,
val description: String?,
val publishedAt: String?,
val source: Source?,
val title: String?,
val url: String?,
val urlToImage: String?
) : Serializable
thus a UNIQUE index (one that does not allow the same value to be stored more than once) would be created and maintained on the url column.
Note NULL is not considered a duplicate value (that is a NULL is considered to be different to any other NULL), so if this value can be null then perhaps it is not a wise choice.
However, you may decide that multiple columns should constitute a duplicate to not be inserted. Here's a variation showing how multiple columns (composite index) can be used.
#Entity( tableName = "articles", indices = [Index(value = ["author","content","description"],unique = true)] ) //<<<<<<<<< ONLY CHANGE IS THE #Entity
data class Article(
#PrimaryKey(autoGenerate = true)
var Id: Int? = null,
val author: String?,
val content: String?,
val description: String?,
val publishedAt: String?,
val source: Source?,
val title: String?,
val url: String?,
val urlToImage: String?
) : Serializable
in this case if the author, content and description were the same then it would be a duplicate.
Note in all cases allowing all null values (? after all) could be problematic if there is no validation to stop all values being null (i.e. the data would probably be useless).
You may also wish to consider clearing inputs (some only perhaps) after an insertion, thus making it less likely for a duplicate to be attemtped.

Related

How do I create a new record in Android Room database?

This seems like a lazy question, but the offical docs literally don't explain how to do this.
https://developer.android.com/training/data-storage/room
I have an entity like so:
#Entity
data class Shader(
#PrimaryKey(autoGenerate = true) val uid: Int,
val name: String,
val shaderMainText: String,
val paramsJson: String?
)
And some methods on my Dao:
#Insert
fun insertAll(vararg shaders: Shader)
#Delete
fun delete(shader: Shader)
#Update
fun update(shader: Shader)
How do I make a new record and insert it?
I've gotten so far as this:
val record = Shader(name="Foo", shaderMainText="bar", paramsJson=null)
But it complains that I'm missing the argument uid. Why do I need to provide a uid? It's supposed to be auto-generated?
An example of creating a new record would be appreciated.
You can set 0 for the default value of your uid field
#Entity
data class Shader(
#PrimaryKey(autoGenerate = true) val uid: Int = 0,
val name: String,
val shaderMainText: String,
val paramsJson: String?
)
When autoGenerate is true, Room ignores the default value, so it creates auto-incremented values.
Finally, this doesn't give you a compilation error:
val record = Shader(name="Foo", shaderMainText="bar", paramsJson=null)
The docs say:
If the field type is long or int (or its TypeConverter converts it to a long or int), Insert methods treat 0 as not-set while inserting the item.
If the field's type is Integer or Long (or its TypeConverter converts it to an Integer or a Long), Insert methods treat null as not-set while inserting the item.
So I would try setting the uid to be initialized to 0 or make it nullable and set to null.
Hope that helps!
https://developer.android.com/reference/android/arch/persistence/room/PrimaryKey#autoGenerate()
You Can Also try like this
The best practice is you always create an instance Class
1st Create a Database instance class
#Database(entities = [Shader::class], version = 1)
abstract class DatabaseHelper : RoomDatabase() {
companion object {
private var instance: DatabaseHelper? = null
fun getInstance(context: Context?): DatabaseHelper? {
if (instance == null) {
synchronized(DatabaseHelper::class) {
if (context != null) {
instance = Room.databaseBuilder(context.applicationContext, DatabaseHelper::class.java, "database.db").allowMainThreadQueries().build()
}
}
}
return instance
}
}
abstract fun getDao(): DBDao?
}
Create Your Shader data class like below
#Entity(tableName = "shader")
data class Shader(
#PrimaryKey(autoGenerate = true) var id: Int?,
val name: String,
val shaderMainText: String,
val paramsJson: String?
) {
constructor(name: String, shaderMainText: String, paramsJson: String?) : this(
null,
name,
shaderMainText,
paramsJson
)
}
Here you want to create constructor
Add data in Shader and insertAll Like Below
val record = Shader(name="Foo", shaderMainText="bar", paramsJson=null)
DatabaseHelper.getInstance(this)?.getDao()?.insertAll(record)
And Your Data added is successfully
There should be always a #PrimaryKey(autoGenerate = false) while inserting data in the DB

How can I get the desired object with sql from a many-to-many relationship table?

i'm android beginner developer. i am createing stationArrivalInformation App.
#Entity
data class StationEntity(
#PrimaryKey val stationName: String,
val isFavorite: Boolean = false
)
#Entity
data class SubwayEntity(
#PrimaryKey val subwayId: Int
)
#Entity(primaryKeys = ["stationName", "subwayId"])
data class StationSubwayCrossRefEntity(
val stationName: String,
val subwayId: Int
)
data class StationWithSubwaysEntity(
#Embedded val station: StationEntity,
#Relation(
parentColumn = "stationName",
entityColumn = "subwayId",
entity = SubwayEntity::class,
associateBy = Junction(
StationSubwayCrossRefEntity::class,
parentColumn = "stationName",
entityColumn = "subwayId"
)
)
val subways: List<SubwayEntity>
)
i have built a data class with a many-to-many relationship.
1. station Table
enter image description here
2. subway Table
enter image description here
3. cross Ref Table
enter image description here
if you look at the DAO File:
#Dao
interface StationDao {
#Transaction
#Query("SELECT * FROM StationEntity")
fun getStationWithSubways(): Flow<List<StationWithSubwaysEntity>>
#Insert(onConflict = REPLACE)
suspend fun insertStations(station: List<StationEntity>)
#Insert(onConflict = REPLACE)
suspend fun insertSubways(subway: List<SubwayEntity>)
#Insert(onConflict = REPLACE)
suspend fun insertCrossRef(refEntity: List<StationSubwayCrossRefEntity>)
#Transaction
#Insert(onConflict = REPLACE)
suspend fun insertStationSubways(stationSubways: List<Pair<StationEntity, SubwayEntity>>) {
insertStations(stationSubways.map { it.first })
insertSubways(stationSubways.map { it.second })
insertCrossRef(stationSubways.map { (station, subway) ->
StationSubwayCrossRefEntity(
station.stationName, subway.subwayId
)
})
}
#Update
suspend fun updateStation(station: StationEntity)
}
class StationRepositoryImpl #Inject constructor(
private val stationDao: StationDao
): StationRepository {
override val stations: Flow<List<Station>> =
stationDao.getStationWithSubways()
.distinctUntilChanged()
.map { stations -> stations.toStation().sortedByDescending { it.isFavorite } }
.flowOn(dispatcher)
}
here, the result of stationDao.getStationWithSubways() is null. I referred to the Android official documentation and applied it, but I am not getting the desired result. Why?
i expected getting multiple subways at one station
enter image description here
<Type of the parameter must be a class annotated with #Entity or a collection/array of it.>
-> how solve?
Room does not anything (according to the classes shown) about the Station class and thus it does not know how to handle:-
#Update
suspend fun updateStation(station: Station)
As there is no such #Entity annotated class.
The fix I believe is to use
#Update
suspend fun updateStation(station: StationEntity)
if that is what you are trying to update
However, you will then possibly have issues due to the warning that will be in the Build log:-
warning: The affinity of child column (subwayId : INTEGER) does not match the type affinity of the junction child column (subwayId : TEXT). - subways in a.a.so75052787kotlinroomretrievefrommanytomany.StationWithSubwaysEntity
Another warning that you may wish to consider is
warning: The column subwayId in the junction entity a.a.so75052787kotlinroomretrievefrommanytomany.StationSubwayCrossRefEntity is being used to resolve a relationship but it is not covered by any index. This might cause a full table scan when resolving the relationship, it is highly advised to create an index that covers this column. - subwayId in a.a.so75052787kotlinroomretrievefrommanytomany.StationSubwayCrossRefEntity
Both will not appear if you used:-
#Entity(primaryKeys = ["stationName", "subwayId"])
data class StationSubwayCrossRefEntity(
val stationName: String,
//val subwayId: String
#ColumnInfo(index = true)
val subwayId: Int
)
commented out line left in just to show before/after
You would then have to use :-
#Transaction
#Insert(onConflict = REPLACE)
fun insertStationSubways(stationSubways: List<Pair<StationEntity, SubwayEntity>>) {
insertStations(stationSubways.map { it.first })
insertSubways(stationSubways.map { it.second })
insertCrossRef(stationSubways.map { (station, subway) ->
StationSubwayCrossRefEntity(
station.stationName, subway.subwayId
)
})
}
subway.subwayId instead of subway.subwayId.toString()
i expected getting multiple subways at one station in normal operation
You would. With the changes suggested above (and some others to run on the main thread for brevity/convenience), an appropriate #Database annotated class as per:-
#Database(entities = [SubwayEntity::class,StationEntity::class, StationSubwayCrossRefEntity::class], version = 1, exportSchema = false)
abstract class TheDatabase: RoomDatabase() {
abstract fun getStationDao(): StationDao
companion object {
private var instance: TheDatabase?=null
fun getInstance(context: Context): TheDatabase {
if (instance==null) {
instance = Room.databaseBuilder(context,TheDatabase::class.java,"the_database.db")
.allowMainThreadQueries()
.build()
}
return instance as TheDatabase
}
}
}
And the following in an Activity, to demonstrate :-
class MainActivity : AppCompatActivity() {
lateinit var dbInstance: TheDatabase
lateinit var dao: StationDao
override fun onCreate(savedInstanceState: Bundle?) {
super.onCreate(savedInstanceState)
setContentView(R.layout.activity_main)
dbInstance = TheDatabase.getInstance(this)
dao = dbInstance.getStationDao()
dao.insertStationSubways(listOf(Pair(StationEntity("Station1",false),SubwayEntity(1))))
dao.insertStationSubways(listOf(Pair(StationEntity("Station1",false),SubwayEntity(2))))
dao.insertStationSubways(listOf(Pair(StationEntity("Station1",false),SubwayEntity(3))))
dao.insertStationSubways(listOf(Pair(StationEntity("Station2",false),SubwayEntity(4))))
dao.insertStationSubways(listOf(Pair(StationEntity("Station2",false),SubwayEntity(5))))
dao.insertStationSubways(listOf(Pair(StationEntity("Station2",false),SubwayEntity(6))))
val sb = StringBuilder()
for (sws in dao.getStationWithSubways()) {
sb.clear()
for (subway in sws.subways) {
sb.append("\n\tSubway is ${subway.subwayId}")
}
Log.d("DBINFO","Station is ${sws.station.stationName} it has ${sws.subways.size} subways. They are:-${sb}")
}
}
}
Then the log (when run for the first time) includes (as expected):-
D/DBINFO: Station is Station1 it has 3 subways. They are:-
Subway is 1
Subway is 2
Subway is 3
D/DBINFO: Station is Station2 it has 3 subways. They are:-
Subway is 4
Subway is 5
Subway is 6

How can I add data into Room database in a manner where it is appended to the top row

Image for reference
I am facing a situation whenever I add a new article into the database it will add the new article to the bottom of the RecyclerView, how can I implement it in such a way that it updates the top row instead?
Is it something got to do with the Adapter or do I have to tweak the Doa?
Room Database Implementation
**//ViewModel**
fun saveArticle(article: Article) = viewModelScope.launch {
newsRepository.upsert(article)
}
**
//NewsRepository**
suspend fun upsert(article: Article) = db.getArticleDao().upsert(article)
**//Implementation of the Database**
#Database(
entities = [Article::class],
version = 1
)
#TypeConverters(Converters::class)
abstract class ArticleDatabase : RoomDatabase() {
abstract fun getArticleDao(): ArticleDao
companion object {
#Volatile
private var instance: ArticleDatabase? = null
private val LOCK = Any()
operator fun invoke(context: Context) = instance ?: synchronized(LOCK) {
instance ?: createDatabase(context).also { instance = it }
}
private fun createDatabase(context: Context) =
Room.databaseBuilder(
context.applicationContext,
ArticleDatabase::class.java,
"article_db.db"
).build()
}
}
**//DOA**
#Insert(onConflict = OnConflictStrategy.REPLACE)
suspend fun upsert(article: Article): Long //returns the id's of the article
**//Entity**
#Entity(
tableName = "articles", indices = [Index(value = ["url","title"], unique = true)]
)
#Parcelize
data class Article(
#PrimaryKey(autoGenerate = true)
var id: Int? =null,
val author: String?,
val description: String?,
val source: Source?,
val title: String?,
val url: String?,
val urlToImage: String?,
val publishedAt: String?,
val content: String?
): Parcelable {
override fun hashCode(): Int {
var result = id.hashCode()
if(url.isNullOrEmpty()){
result = 31 * result + url.hashCode()
}
return result
}
}
Expecting the top row to be updated instead of the bottom row, the Room Database docs did not talk much about changing the way the article is inserted, tried to reference other people's work, couldn't find the solution

Getting "UNIQUE constraint failed" when using #Upsert in Android Room

Getting net.sqlcipher.database.SQLiteConstraintException: error code 19: UNIQUE constraint failed with : appointment.activity_id: when trying to do #Upsert with Android Room.
My understanding with #Upsert is that it will update records if a row exists or insert if it doesn't.
Here is the definition of the table:
data class AppointmentEntity(
#PrimaryKey
#field:ColumnInfo(name = "activity_id")
val activityId: Long,
#field:ColumnInfo(name = "selected_owner")
val selectedOwner: String,
val activityStartTimestamp: Instant,
val activityEndTimestamp: Instant,
val activityRevisionTimestamp: Instant?,
val appointmentTypeCode: AppointmentTypeCode,
val contactName: String?,
val activityDescription: String?,
val recurringId: Long?,
val cancelled: Boolean,
val personalAppointment: Boolean,
val outlookIndicator: Boolean,
val allDayEvent: Boolean,
val deleteDate: Instant?
)
Here is the code in the #Dao:
#Upsert
fun insertAppointments(appointment: List<AppointmentEntity>)
Why am I getting a unique constraint error. Wouldn't an existing record just be updated instead of reinserted?
From the android docs:
If the target entity contains a PrimaryKey that is auto generated, then the POJO class doesn't need an equal primary key field, otherwise primary keys must also be present in the POJO. If the primary key already exists, only the columns represented by the partial entity fields will be updated
There appears to be a conflict between Android room 2.5.0 and sqlcipher. As soon as I removed the sqlcipher SupportFactory from my room database the upsert worked as expected.
This appears to be the root cause: https://github.com/sqlcipher/android-database-sqlcipher/issues/588. SqlCipher isn't extending android.database.SQLException so when Room checks if the exception is a foreign/unique key here: https://android-review.googlesource.com/c/platform/frameworks/support/+/2191947/9/room/room-runtime/src/main/java/androidx/room/EntityUpsertionAdapter.kt#209 it just always throws the net.sqlcipher.database.SQLException Unique Key Exception rather than Upserting the existing record.
My understanding with #Upsert is that it will update records if a row exists or insert if it doesn't.
It should do and using your available code, but modified to not utilise type converters, it does. e.g. using:-
#Entity(tableName = "appointment")
data class AppointmentEntity(
#PrimaryKey
#field:ColumnInfo(name = "activity_id")
val activityId: Long,
#field:ColumnInfo(name = "selected_owner")
val selectedOwner: String,
val activityStartTimestamp: Long?=System.currentTimeMillis() / 1000, /*<<<< CHANGED FROM Instant */
val activityEndTimestamp: Long?=System.currentTimeMillis() / 1000, /*<<<< CHANGED FROM Instant */
val activityRevisionTimestamp: Long?=System.currentTimeMillis() / 1000, /*<<<< CHANGED FROM Instant */
//val appointmentTypeCode: AppointmentTypeCode, /*<<<<< COMMENTED OUT */
val contactName: String?,
val activityDescription: String?,
val recurringId: Long?,
val cancelled: Boolean,
val personalAppointment: Boolean,
val outlookIndicator: Boolean,
val allDayEvent: Boolean,
val deleteDate: Long?=null /*<<<< CHANGED FROM Instant */
)
#Database(entities = [AppointmentEntity::class], exportSchema = false, version = 1)
abstract class TheDatabase: RoomDatabase() {
abstract fun getAllDao(): AllDao
companion object {
private var instance: TheDatabase?=null
fun getInstance(context: Context): TheDatabase {
if (instance==null) {
instance = Room.databaseBuilder(context,TheDatabase::class.java,"the_database.db")
.allowMainThreadQueries()
.build()
}
return instance as TheDatabase
}
}
}
#Dao
interface AllDao {
#Upsert
fun insertAppointments(appointment: List<AppointmentEntity>)
}
and :-
class MainActivity : AppCompatActivity() {
lateinit var db: TheDatabase
lateinit var dao: AllDao
override fun onCreate(savedInstanceState: Bundle?) {
super.onCreate(savedInstanceState)
setContentView(R.layout.activity_main)
var appointmentEntity1 = AppointmentEntity(activityId = 1, selectedOwner = "O001", contactName = "C001", recurringId = 0, cancelled = false, activityDescription = "Desc001", personalAppointment = true, outlookIndicator = false, allDayEvent = false)
var appointmentEntity2 = AppointmentEntity(activityId = 1, selectedOwner = "O001", contactName = "C002", recurringId = 0, cancelled = false, activityDescription = "Desc002", personalAppointment = true, outlookIndicator = false, allDayEvent = false)
db = TheDatabase.getInstance(this)
dao = db.getAllDao()
dao.insertAppointments(listOf(appointmentEntity1,appointmentEntity2,appointmentEntity1,appointmentEntity2))
}
}
Results in a successful run with App Inspection showing :-
i.e. it has coped with the 4 UPSERTS and the resultant data is as expected.
The issue is likely elsewhere. Perhaps because you appear to be using sqlcipher or perhaps other database actions.

Problem in TypeConverters In Room Database

I am trying to use type converters in Android (Kotlin) so i am using the type converters class but i am getting confused like inside of the clouds i am having a single variable so i have returned it but
#Entity(tableName = "WeatherDb")
data class WeatherDTO(
val base: String,
val clouds: Clouds,
val cod: Int,
val coord: Coord,
val dt: Int,
#PrimaryKey(autoGenerate = true)
val id: Int,
val main: Main,
val name: String,
val sys: Sys,
val timezone: Int,
val visibility: Int,
val weather: List<Weather>,
val wind: Wind
)
class TypeConverters {
#TypeConverter
fun fromCloudsToDouble(clouds: Clouds): Int {
return clouds.all
}
fun fromCoordToDouble(coord: Coord): Double {
}
}
In coord class here are multiple with different datatypes how to covert this?
data class Main(
val feels_like: Double,
val grnd_level: Int,
val humidity: Int,
val pressure: Int,
val sea_level: Int,
val temp: Double,
val temp_max: Double,
val temp_min: Double
)
Clouds.kt
data class Clouds(
val all: Int
)
Coord.kt
data class Coord(
val lat: Double,
val lon: Double
)
Main.kt
data class Main(
val feels_like: Double,
val grnd_level: Int,
val humidity: Int,
val pressure: Int,
val sea_level: Int,
val temp: Double,
val temp_max: Double,
val temp_min: Double
)
Sys.kt
data class Sys(
val country: String,
val id: Int,
val sunrise: Int,
val sunset: Int,
val type: Int
)
Weather.kt
data class Weather(
val description: String,
val icon: String,
val id: Int,
val main: String
)
Wind.kt
data class Wind(
val deg: Int,
val gust: Double,
val speed: Double
)
WeatherViewModel.kt
#HiltViewModel
class WeatherViewModel #Inject constructor(
private val repo:WeatherRepository,
private val application: Application,
private val WeatherDb:WeatherDB,
private val fusedLocationProviderClient: FusedLocationProviderClient
) :ViewModel(){
private val _resp = MutableLiveData<WeatherDTO>()
val weatherResp:LiveData<WeatherDTO>
get() = _resp
private val _cord = MutableLiveData<Coord>()
val cord:LiveData<Coord>
get() = _cord
var locality:String = ""
fun getWeather(latitude:Double,longitude:Double) =
viewModelScope.launch {
repo.getWeather(latitude,longitude).let { response->
if(response.isSuccessful){
Log.d("response","${response.body()}")
WeatherDb.WeatherDao().insertWeather(response.body()!!)
_resp.postValue(response.body())
}else{
Log.d("Weather Error","getWeather Error Response: ${response.message()}")
}
}
}
fun fetchLocation():Boolean{
val task = fusedLocationProviderClient.lastLocation
if(ActivityCompat.checkSelfPermission(application,android.Manifest.permission.ACCESS_FINE_LOCATION)
!=PackageManager.PERMISSION_GRANTED &&
ActivityCompat.checkSelfPermission(application,android.Manifest.permission.ACCESS_COARSE_LOCATION)
!=PackageManager.PERMISSION_GRANTED
){
return true
}
task.addOnSuccessListener {
if(it!=null){
getWeather(it.latitude,it.longitude)
getAddressName(it.latitude,it.longitude)
Log.d("localityname", locality)
}
}
return true
}
private fun fetchLocationDetails(){
}
private fun getAddressName(lat:Double,long:Double):String{
var addressName = " "
val geoCoder = Geocoder(application, Locale.getDefault())
val address = geoCoder.getFromLocation(lat,long,1)
if (address != null) {
addressName = address[0].adminArea
}
locality = addressName
Log.d("subadmin",addressName.toString())
Log.d("Address", addressName)
return addressName
}
fun getCoordinates(cord:String){
val geocoder = Geocoder(application,Locale.getDefault())
val address = geocoder.getFromLocationName(cord,2)
val result = address?.get(0)
if (result != null) {
getWeather(result.latitude,result.longitude)
getAddressName(result.latitude,result.longitude)
}
}
}
Here is my converter in the Kotlin:
class Converters {
#TypeConverter
fun valueFromDomainToStorage(value: Value): String {
return value.convertToJson()
}
#TypeConverter
fun valueFromStorageToDomain(str: String): Value {
// we can not create an empty instance of value as TypeDecoder.java should call non-empty constructor
return Value(
"just a stub",
BigInteger.valueOf(0),
BigInteger.valueOf(0),
false,
BigInteger.valueOf(0)
)
.fromJson(str)
}
}
where .convertToJson() and .fromJson(str) implemented as extensions within Value class:
fun Value.convertToJson(): String {
val result = JSONObject()
result.put(ValueConst.OFFER_FIELD, offer)
result.put(ValueConst.AVAILABLE_SINCE, availableSince.toLong())
result.put(ValueConst.AVAILABLE_END, availabilityEnd.toLong())
result.put(ValueConst.IS_CONSUMED, isConsumed)
result.put(ValueConst.LOCKED_UNTIL, lockedUntil)
return result.toString()
}
fun Value.fromJson(json: String): Value {
val subj = JSONObject(json)
return Value(
subj.optString(ValueConst.OFFER_FIELD),
BigInteger.valueOf(subj.optLong(ValueConst.AVAILABLE_SINCE)),
BigInteger.valueOf(subj.optLong(ValueConst.AVAILABLE_END)),
subj.optBoolean(ValueConst.IS_CONSUMED),
BigInteger.valueOf(subj.optLong(ValueConst.LOCKED_UNTIL))
)
}
You should implement Converter class for each non-native class type. Do not forget to register your converters on database:
#Database(entities = [ChainTransaction::class], version = 1, exportSchema = false)
#TypeConverters(Converters::class)
abstract class AppDatabase: RoomDatabase() {
When you have compile the code and later introduce new changes, you have to increase version parameter too to make changes to take effect:
#Database(entities = [ChainTransaction::class], version = 2, exportSchema = false)
#TypeConverters(Converters::class)
abstract class AppDatabase: RoomDatabase() {
Here is official documentation and even training on this topic:
https://developer.android.com/training/data-storage/room
so i am using the type converters class but i am getting confused
SQLite (the database around which Room is an object orientated wrapper) is not an object orientated (or aware) database. It is a database that can store primitive types of data which are one of
INTEGER (such as Int or Long), REAL
REAL (such as Float or Double)
TEXT (such as String)
BLOB (such as ByteArray)
NULL
Therefore to store a type of Coord, Cloud or Weather .... you have three options:-
to embed the class, in which case the fields are copied from the embedded class (would be complicated if the embedded classes contained unsupported types). not covered in the answer
to have the class as a table in it's own right with a relationship between it and the parent (WeatherDTO). not covered in the answer
to convert the class to one of the SQLite types (of which either TEXT or BLOB would probably only be practical).
Considering option 3 (TyepConverters) converting the data is of little, if any, use just storing the data as you would not be able to retrieve the data.
As such type converters should always be paired.
One of the pair will be to convert from the class to a type that can be stored.
The other will be to convert from the stored type to the class.
As such you will need quite a few type Converters, that is 2 each for fields:-
clouds (class Clouds)
coord (class Coord)
main (class Main)
sys (class Sys)
weather (class List)
wind (class Wind)
It is the Class of the field that Room looks at to locate the respective type converter.
One of the simplest ways to convert objects (aka classes) is to convert the object to a JSON representation. Although a complexity with this is that there are many JSON libraries and they will often have differences.
For the examples that follow Googles JSON library has been used. However, use of this library with Room doesn't appear to directly support the use of List<the_class> e.g. List.
The dependency for this being (as an example) implementation 'com.google.code.gson:gson:2.10'
As a get around a new class WeatherList has ben used as per:-
data class WeatherList(
val weatherList: List<Weather>
)
and the WeatherDTO class has been changed to use it as per :-
....
//val weather: List<Weather>,
val weather: WeatherList,
....
As such the TypeConverters class could then be:-
class TypeConverters {
#TypeConverter
fun fromCloudsToJSONString(clouds: Clouds): String = Gson().toJson(clouds)
#TypeConverter
fun toCloudsFromJSONString(jsonString: String): Clouds = Gson().fromJson(jsonString,Clouds::class.java)
#TypeConverter
fun fromCoordToJSONString(coord: Coord): String = Gson().toJson(coord)
#TypeConverter
fun toCoordFromJSONString(jsonString: String): Coord = Gson().fromJson(jsonString,Coord::class.java)
#TypeConverter
fun fromMaintoJSONString(main: Main): String = Gson().toJson(main)
#TypeConverter
fun toMainFromJSONString(jsonString: String): Main = Gson().fromJson(jsonString,Main::class.java)
#TypeConverter
fun fromSysToJSONString(sys: Sys): String = Gson().toJson(sys)
#TypeConverter
fun toSysFromJSONString(jsonString: String): Sys = Gson().fromJson(jsonString,Sys::class.java)
#TypeConverter
fun fromWeatherListFromJSONString(weatherList: WeatherList): String = Gson().toJson(weatherList)
#TypeConverter
fun toWeatherListFromJSOnString(jsonString: String): WeatherList = Gson().fromJson(jsonString,WeatherList::class.java)
#TypeConverter
fun fromWindToJSONString(wind: Wind): String = Gson().toJson(wind)
#TypeConverter
fun toWindFromJSONString(jsonString: String): Wind = Gson().fromJson(jsonString,Wind::class.java)
}
As such the all the types/classes/objects that are not directly supported are converted to/from a JSON string representation of the type/class/object.
Note that you need to add the #TypeConverters(#TypeConverters( value = [<????>.TypeConverters::class]). Where has to distinguish between your projects TypeConverters class from Room's (TypeConverters is probably not the best name for the class, renaming it, would overcome the need to distinguish)
Working Example
The following puts the above into action.
As the question does not include the underlying classes, the following have been used:-
data class Coord(
val longitude: Double,
val latitude: Double
)
data class Clouds(
val cover: Double,
val type: String
)
data class Main(
val main: Double
)
data class Sys(
val sys: Double
)
data class WeatherList(
val weatherList: List<Weather>
)
data class Weather(
val weather: Double
)
data class Wind(
val wind: Double
)
The #Dao annotated interface was also made up and is simply:-
#Dao
interface AllDao {
#Insert(onConflict = OnConflictStrategy.IGNORE)
fun insert(weatherDTO: WeatherDTO)
#Query("SELECT * FROM weatherdb")
fun getAllFromWeatherDB(): List<WeatherDTO>
}
Also the #Database annotated abstract class was made up it being:-
#TypeConverters( value = [a.a.so74384736typeconverterconfusion.TypeConverters::class])
#Database(entities = [WeatherDTO::class], exportSchema = false, version = 1)
abstract class TheDatabase: RoomDatabase() {
abstract fun getAllDao(): AllDao
companion object {
private var instance: TheDatabase? = null
fun getInstance(context: Context): TheDatabase {
if (instance==null) {
instance = Room.databaseBuilder(context,TheDatabase::class.java,"the_database.db")
.allowMainThreadQueries()
.build()
}
return instance as TheDatabase
}
}
}
Note the package name used to distinguish the TypeConverters class from Room's TypeConverters class
the package name cannot be used elsewhere, so if the above is copied then it would have to be changed. There is no expectation that the code in it's entirety would be copied and used. The code is designed solely to demonstrate the TypeConverters.
Last some activity code to actually do something (store and retrieve some data):-
class MainActivity : AppCompatActivity() {
lateinit var db: TheDatabase
lateinit var dao: AllDao
override fun onCreate(savedInstanceState: Bundle?) {
super.onCreate(savedInstanceState)
setContentView(R.layout.activity_main)
db = TheDatabase.getInstance(this)
dao = db.getAllDao()
dao.insert(
WeatherDTO(
"base001",
Clouds(25.5,"cumulus"),10,
Coord(10.567,30.345),
11,
12,
Main(12345.67890),
"thename",
Sys(9.87654321),
14,
1000,
WeatherList(listOf(Weather(5.1234),Weather(6.5432), Weather(7.6543))),
Wind(23.12)
)
)
for (wdto in dao.getAllFromWeatherDB()) {
Log.d("DBINFO","base = ${wdto.base} longitude = ${wdto.coord.longitude} latitude = ${wdto.coord.latitude} etc ....")
}
}
}
RESULT
When run the log contains, as expected:-
D/DBINFO: base = base001 longitude = 10.567 latitude = 30.345 etc ....
Using App Inspection then the database looks like:-
The fields converted to a JSON string have been highlighted.
Obviously the data will very likely not exactly be as you would expect due to the made up classes.
Follow on from the previous answer #Embedded versus Type Converters
As can be seen from the previous answer, there are some issues in regard to using TypeConverters. From a database perspective the TypeConverters will inevitably contain bloat/unecessary data which is contrary to normalisation (not needlessly storing repetitive data).
As an example the JSON representation will for every row contain exactly the same the field names wasting storage, all rows will have the additional overhead of storing the delimiters ([s and ]s, {s and }s, :s ,s). Furthermore actually using the stored data can become complex due to the bloat and also due to multiple values being stored in a single column and as such can be restrictive.
It would be more efficient to not store the bloat and it could eliminate complexities and enhance the usability of the stored data from a database perspective (querying the data for retrieval) to not store multiple values in a single column.
Using the #Embedded annotation can very easily eliminate the bloat. Consider the following (an alternative version of the WeatherDTO class/entity):-
#Entity(tableName = "WeatherDbAlternative1")
data class WeatherDTOAlternative1(
val base: String,
#Embedded
val clouds: Clouds,
val cod: Int,
#Embedded
val coord: Coord,
val dt: Int,
#PrimaryKey(autoGenerate = true)
val id: Int,
#Embedded
val main: Main,
val name: String,
#Embedded
val sys: Sys,
val timezone: Int,
val visibility: Int,
//val weather: List<Weather>,
/* Unable to embed directly so not embedding */
val weather: WeatherList,
#Embedded
val wind: Wind
)
Bar the weather field all that has been done is add the #Embedded annotation. Noting that the classes of the fields all have fields of types directly supported by Room.
Adding this entity to the #Database annotation and adding a couple of additional functions in the #Dao annotated class as per:-
#Query("SELECT * FROM weatherdbalternative1")
fun getAllFromWeatherDBAlternative1(): List<WeatherDTOAlternative1>
#Insert(onConflict = OnConflictStrategy.IGNORE)
fun insert(weatherDTOAlternative1: WeatherDTOAlternative1)
And then amending the Activity code to include :-
/*ALTERNATIVE 1 All but WeatherList embedded */
dao.insert(
WeatherDTOAlternative1(
"base001A",
Clouds(25.5, "cumulus"),
10,
Coord(10.567, 30.345),
11,
12,
Main(12345.67890),
"thenameA1",
Sys(9.87654321),
14,
1000,
WeatherList(listOf(Weather(5.1234), Weather(6.5432), Weather(7.6543))),
Wind(23.12)
)
)
for (wdto in dao.getAllFromWeatherDBAlternative1()) {
Log.d(
"DBINFO",
"base = ${wdto.base} longitude = ${wdto.coord.longitude} latitude = ${wdto.coord.latitude} etc ...."
)
}
Now results in the Log including:-
D/DBINFO: base = base001 longitude = 10.567 latitude = 30.345 etc ....
D/DBINFO: base = base001A longitude = 10.567 latitude = 30.345 etc ....
i.e. effectively the same data is stored and retrievable
However the data is now stored in the database as (ignoring the weather field) as :-
i.e. the data stored is much cleaner but at the expense of additional columns (which can be advantageous).
additionally although not apparent, the fields that have the #Embedded annotation do not need the TypeConverters.

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