Develop Reference

Mapping database model to Ui model

I try to make the project based on clean architecture so that each layer could have its own data model.
I have a database that contains 2 Entities: "movie" and "details".
#Entity(tableName = "movie")
data class MovieDbModel(
var page: Int,
#PrimaryKey(autoGenerate = false)
var id: Int,
var poster_path: String,
var overview: String,
var original_title: String)
#Entity(tableName = "details")
data class DetailsDbModel (
#PrimaryKey(autoGenerate = false)
val id: Int,
val genres: Genres,
val runtime: Int,
)
I want to map those 2 entities to 1 UI model "MovieAndDetailsUi " and convert it to MutableList that I will use for liveData.
data class MovieAndDetailsUi (
val page: Int,
val id: Int,
val poster_path: String,
val overview: String,
val original_title: String,
val genres: List<GenreUi>,
val runtime: Int,
)
But I have problems with that. Could you please show me the best way to do that? Thank you.

If you want to map those two you could create a companion object on the MoviesAndDetailsUi class that takes both entities and combines them, for example
data class MovieAndDetailsUi (
val page: Int,
val id: Int,
val poster_path: String,
val overview: String,
val original_title: String,
val genres: List<GenreUi>,
val runtime: Int,
) {
companion object {
fun fromDatabaseEntities(movie: MovieDbModel, details: DetailsDbModel) {
return MovieAndDetailsUI(
page = movie.page,
id = movie.id,
poster_path = movie.poster_path,
overview = movie.overview,
original_title = movie.original_title,
genres = details.genres,
runtime = details.runtime
)
}
}
}
That way on your view model you could just get the data from the DB and map it to the UI class, for example:
fun getMovies(): MutableList<MovieAndDetailsUi>() =
viewModelScope.launch() {
withContext(Dispatches.IO) {
val movies: List<MovieDbModel> = ... // Access the DB and get the movies
val details: List<DetailsDbModel = ... // Access the DB and get the details
val zipData = movies.zip(details) {movie, detail -> Pair(movie, detail)}
val mappedData = zipData.map { pair -> MovieAndDetailsUi.fromDatabaseEntities(pair.first, pair.second) }.toMutableList()
liveData.postValue(mappedData)
}
}
I also agree that in this case you should go with the flat structure on the entities as you can skip the mapping and also avoid having multiple classes with the same attributes basically, but in case you want to go this way here's how. Also, I don't know how you are associating the details and movie table and how you query the tables, you might have a problem there too as there's no foreing key on movies referencing to details or vice versa. I added the zip function just for the example but you should have a proper way to associate the movies and the details objects

TypeConverter function never used room database

I have list of custom object that i wanna save it in the database.
So I have to use TypeConverters to make this possible.
My problem that i get an error when I implement the functionality and I noticed
that a function annotated with TypeConverter never used
Here's the error:
A failure occurred while executing org.jetbrains.kotlin.gradle.internal.KaptExecution
error: The columns returned by the query does not have the fields [avatar,email,first_name,id,last_name] in com.hraa.fakeusers.model.UserData even though they are annotated as non-null or primitive. Columns returned by the query: [data]
public abstract androidx.lifecycle.LiveData<java.util.List<com.hraa.fakeusers.model.UserData>> getUsers();
And here's the code:
#Entity(tableName = USER_DATA_TABLE)
data class DataModel(
val data: List<UserData>,
val page: Int,
val per_page: Int,
val total: Int,
val total_pages: Int
) {
#PrimaryKey(autoGenerate = true)
var id: Int? = null
}
data class UserData(
val avatar: String,
val email: String,
val first_name: String,
val id: Int,
val last_name: String
)
class Converters {
#TypeConverter
fun toUsersData(value: String): List<UserData> {
val type = object : TypeToken<List<UserData>>() {}.type
return Gson().fromJson(value, type)
}
#TypeConverter
fun fromUsersData(usersData: List<UserData>): String {
return Gson().toJson(usersData)
}
}
#Database(entities = [DataModel::class], version = 1, exportSchema = false)
#TypeConverters(Converters::class)
abstract class AppDatabase: RoomDatabase() {
abstract fun dataDao(): DataDao
}
#Dao
interface DataDao {
#Insert(onConflict = OnConflictStrategy.REPLACE)
suspend fun insertData(data: DataModel)
#Delete
suspend fun deleteData(data: DataModel)
#Query("SELECT data FROM USER_DATA_TABLE")
fun getUsers(): LiveData<List<UserData>>
}
Note: toUsersData() function never used.. I don't know why.

Note: toUsersData() function never used
How can you be sure of that? My guess is that this function could work well, but you have two type's transformations here:
#Query("SELECT data FROM USER_DATA_TABLE")
fun getUsers(): LiveData<List<UserData>>
Transformation #1 (row level). Input: String (saved in db). Output: data (List).
That should be processed well thanks to your toUsersData() method (may be not, I've not checked, but it seems it should do)
Transformation #2 (row level). Input: data (List). Output: UserData (According to your desired return type). For that Room doesn't know how to do this transformation, so you have en error.
To check if your toUsersData() really works you can test next query:
#Query("SELECT * FROM USER_DATA_TABLE")
fun getUsers(): LiveData<List<DataModel>>
If your build is successful, then there is no problem with this function. You can also find this function in Java-class, that was autogenerated by Room during build.
You can try to add another data class:
data class UserDataList(
val data: List<UserData>
)
and change your data method to:
#Query("SELECT data FROM USER_DATA_TABLE")
fun getUsers(): LiveData<List<UserDataList>>

Android Kotlin - Storing of Gson casted API data into a Room Database

I am using okhttp to fetch Json data from an API, casting it into Gson for some other purposes, and at the same time, storing of the API data into a Room Database. (It can be storing of the API json data itself, or the casted Gson version) However, I am unsuccessful in this, and hope you could point me to the direction where I am going wrong.
I think i'm missing a typeConverter to convert the data retrieved from API and casted into GSON, to be stored in the Room database. But i'm not sure if i'm correct in this, or if my approach is correct in the first place.
Or could it be an issue with the fact that I have an Entities data class, but gsonData is casted into SampleData data class?
DataGetter
...
...
...
// this suspend function is run within a coroutine.
private suspend fun APICall(url: String, pageNumber: Int, context: Context){
val urlRequest = Request.Builder().url(url).build() // Building of the URL to fetch data
httpClient.newCall(urlRequest).enqueue(object : Callback {
// onFailure -> cutting this out to shorten code
// onResponse is where I am fetching the data and calling put to DB
override fun onResponse(call: Call, response: Response) {
val dataString = response.body!!.string()
val gsonData = gsonResult.fromJson(dataString, SampleData::class.java)
// Do some other stuffs with gsonData separately. This doesn't return anything to gsonData.
putToRoomDb(gsonData, context) // This will eventually be done via another coroutine.
}
}
}
private suspend fun putToRoomDb(sampleData: SampleData, context: Context) {
val db = MyOnlyDatabase.getInstance(context)
db.MyOnlyDao().updateOrInsert(sampleData)
}
Entity
#Entity(tableName = "sample_data_code_names")
data class SampleDataEntities(
#PrimaryKey
var Code: Int,
val Name: String,
val Description: String,
val Item1: String,
val Item2: String
)
Dao
#Dao
interface SampleDataDao {
#Insert(onConflict = OnConflictStrategy.REPLACE)
suspend fun updateOrInsert(sampleDataEntities: SampleDataEntities)
}
Database
#Database(entities = [SampleDataEntities::class], version = 1, exportSchema = false)
abstract class MyOnlyDatabase: RoomDatabase() {
abstract fun sampleDataDao(): SampleDataDao
companion object {
#Volatile
private var instance: MyOnlyDatabase? = null
fun getInstance(context: Context): MyOnlyDatabase{
return instance ?: synchronized(this) {
instance ?: buildDatabase(context).also { instance = it }
}
}
private fun buildDatabase(context: Context): MyOnlyDatabase{
return Room.databaseBuilder(context, MyOnlyDatabase::class.java, "MyOnlyDatabase.db")
.fallbackToDestructiveMigration()
.build()
}
}
}
Note: Below is the data class for which gsonData is casted into.
data class SampleData(val value: List<SampleDataInfoItems>)
data class SampleDataInfoItems(
val Code: String,
val Name: String,
val Description: String,
val Item1: BigDecimal,
val Item2: BigDecimal
)

You are not annotating your fields according to the JSON response that is coming from the server.
data class SampleDataInfoItems(
#SerializedName("name_this_field_on_json")
val Code: String,
#SerializedName("and_so_on_for_all_fields")
val Name: String,
val Description: String,
val Item1: BigDecimal,
val Item2: BigDecimal
)
Also I think you need the GsonConververFactory for Retrofit.

Android Room, how to save an entity with one of the variables being a sealed class object

I want to save in my Room database an object where one of the variables can either be of on type or another. I thought a sealed class would make sense, so I took this approach:
sealed class BluetoothMessageType() {
data class Dbm(
val data: String
) : BluetoothMessageType()
data class Pwm(
val data: String
) : BluetoothMessageType()
}
Or even this, but it is not necessary. I found that this one gave me even more errors as it did not know how to handle the open val, so if I find a solution for the first version I would be happy anyway.
sealed class BluetoothMessageType(
open val data: String
) {
data class Dbm(
override val data: String
) : BluetoothMessageType()
data class Pwm(
override val data: String
) : BluetoothMessageType()
}
Then the Entity class
#Entity(tableName = MESSAGES_TABLE_NAME)
data class DatabaseBluetoothMessage(
#PrimaryKey(autoGenerate = true)
val id: Long = 0L,
val time: Long = Instant().millis,
val data: BluetoothMessageType
)
I have created a TypeConverter to convert it to and from a String as well, so I assume that it is not a problem.
First, is this possible? I assume this should function in a similar way that it would with an abstract class, but I have not managed to find a working solution with that either. If it is not possible, what sort of approach should I take when I want to save some data that may be either of one or another type if not with sealed classes?

We faced such problem when we tried using Polymorphism in our domain, and we solved it this way:
Domain:
We have a Photo model that looks like this:
sealed interface Photo {
val id: Long
data class Empty(
override val id: Long
) : Photo
data class Simple(
override val id: Long,
val hasStickers: Boolean,
val accessHash: Long,
val fileReferenceBase64: String,
val date: Int,
val sizes: List<PhotoSize>,
val dcId: Int
) : Photo
}
Photo has PhotoSize inside, it looks like this:
sealed interface PhotoSize {
val type: String
data class Empty(
override val type: String
) : PhotoSize
data class Simple(
override val type: String,
val location: FileLocation,
val width: Int,
val height: Int,
val size: Int,
) : PhotoSize
data class Cached(
override val type: String,
val location: FileLocation,
val width: Int,
val height: Int,
val bytesBase64: String,
) : PhotoSize
data class Stripped(
override val type: String,
val bytesBase64: String,
) : PhotoSize
}
Data:
There is much work to do in our data module to make this happen. I will decompose the process to three parts to make it look easier:
1. Entity:
So, using Room and SQL in general, it is hard to save such objects, so we had to come up with this idea. Our PhotoEntity (Which is the Local version of Photo from our domain looks like this:
#Entity
data class PhotoEntity(
// Shared columns
#PrimaryKey
val id: Long,
val type: Type,
// Simple Columns
val hasStickers: Boolean? = null,
val accessHash: Long? = null,
val fileReferenceBase64: String? = null,
val date: Int? = null,
val dcId: Int? = null
) {
enum class Type {
EMPTY,
SIMPLE,
}
}
And our PhotoSizeEntity looks like this:
#Entity
data class PhotoSizeEntity(
// Shared columns
#PrimaryKey
#Embedded
val identity: Identity,
val type: Type,
// Simple columns
#Embedded
val locationLocal: LocalFileLocation? = null,
val width: Int? = null,
val height: Int? = null,
val size: Int? = null,
// Cached and Stripped columns
val bytesBase64: String? = null,
) {
data class Identity(
val photoId: Long,
val sizeType: String
)
enum class Type {
EMPTY,
SIMPLE,
CACHED,
STRIPPED
}
}
Then we have this compound class to unite PhotoEntity and PhotoSizeEntity together, so we can retrieve all data required by our domain's model:
data class PhotoCompound(
#Embedded
val photo: PhotoEntity,
#Relation(entity = PhotoSizeEntity::class, parentColumn = "id", entityColumn = "photoId")
val sizes: List<PhotoSizeEntity>? = null,
)
2. Dao
So our dao should be able to store and retrieve this data. You can have two daos for PhotoEntity and PhotoSizeEntity instead of one, for the sake of flexibility, but in this example we will use a shared one, it looks like this:
#Dao
interface IPhotoDao {
#Transaction
#Query("SELECT * FROM PhotoEntity WHERE id = :id")
suspend fun getPhotoCompound(id: Long): PhotoCompound
#Transaction
suspend fun insertOrUpdateCompound(compound: PhotoCompound) {
compound.sizes?.let { sizes ->
insertOrUpdate(sizes)
}
insertOrUpdate(compound.photo)
}
#Insert(onConflict = OnConflictStrategy.REPLACE)
suspend fun insertOrUpdate(entity: PhotoEntity)
#Insert(onConflict = OnConflictStrategy.REPLACE)
suspend fun insertOrUpdate(entities: List<PhotoSizeEntity>)
}
3. Adapter:
After solving the problem of saving data to SQL database, we now need to solve the problem of converting between domain and local entities. Our Photo's converter aka adapter looks like this:
fun Photo.toCompound() = when(this) {
is Photo.Empty -> this.toCompound()
is Photo.Simple -> this.toCompound()
}
fun PhotoCompound.toModel() = when (photo.type) {
PhotoEntity.Type.EMPTY -> Photo.Empty(photo.id)
PhotoEntity.Type.SIMPLE -> this.toSimpleModel()
}
private fun PhotoCompound.toSimpleModel() = photo.run {
Photo.Simple(
id,
hasStickers!!,
accessHash!!,
fileReferenceBase64!!,
date!!,
sizes?.toModels()!!,
dcId!!
)
}
private fun Photo.Empty.toCompound(): PhotoCompound {
val photo = PhotoEntity(
id,
PhotoEntity.Type.EMPTY
)
return PhotoCompound(photo)
}
private fun Photo.Simple.toCompound(): PhotoCompound {
val photo = PhotoEntity(
id,
PhotoEntity.Type.SIMPLE,
hasStickers = hasStickers,
accessHash = accessHash,
fileReferenceBase64 = fileReferenceBase64,
date = date,
dcId = dcId,
)
val sizeEntities = sizes.toEntities(id)
return PhotoCompound(photo, sizeEntities)
}
And for the PhotoSize, it looks like this:
fun List<PhotoSize>.toEntities(photoId: Long) = map { photoSize ->
photoSize.toEntity(photoId)
}
fun PhotoSize.toEntity(photoId: Long) = when(this) {
is PhotoSize.Cached -> this.toEntity(photoId)
is PhotoSize.Empty -> this.toEntity(photoId)
is PhotoSize.Simple -> this.toEntity(photoId)
is PhotoSize.Stripped -> this.toEntity(photoId)
}
fun List<PhotoSizeEntity>.toModels() = map { photoSizeEntity ->
photoSizeEntity.toModel()
}
fun PhotoSizeEntity.toModel() = when(type) {
PhotoSizeEntity.Type.EMPTY -> this.toEmptyModel()
PhotoSizeEntity.Type.SIMPLE -> this.toSimpleModel()
PhotoSizeEntity.Type.CACHED -> this.toCachedModel()
PhotoSizeEntity.Type.STRIPPED -> this.toStrippedModel()
}
private fun PhotoSizeEntity.toEmptyModel() = PhotoSize.Empty(identity.sizeType)
private fun PhotoSizeEntity.toCachedModel() = PhotoSize.Cached(
identity.sizeType,
locationLocal?.toModel()!!,
width!!,
height!!,
bytesBase64!!
)
private fun PhotoSizeEntity.toSimpleModel() = PhotoSize.Simple(
identity.sizeType,
locationLocal?.toModel()!!,
width!!,
height!!,
size!!
)
private fun PhotoSizeEntity.toStrippedModel() = PhotoSize.Stripped(
identity.sizeType,
bytesBase64!!
)
private fun PhotoSize.Cached.toEntity(photoId: Long) = PhotoSizeEntity(
PhotoSizeEntity.Identity(photoId, type),
PhotoSizeEntity.Type.CACHED,
locationLocal = location.toEntity(),
width = width,
height = height,
bytesBase64 = bytesBase64
)
private fun PhotoSize.Simple.toEntity(photoId: Long) = PhotoSizeEntity(
PhotoSizeEntity.Identity(photoId, type),
PhotoSizeEntity.Type.SIMPLE,
locationLocal = location.toEntity(),
width = width,
height = height,
size = size
)
private fun PhotoSize.Stripped.toEntity(photoId: Long) = PhotoSizeEntity(
PhotoSizeEntity.Identity(photoId, type),
PhotoSizeEntity.Type.STRIPPED,
bytesBase64 = bytesBase64
)
private fun PhotoSize.Empty.toEntity(photoId: Long) = PhotoSizeEntity(
PhotoSizeEntity.Identity(photoId, type),
PhotoSizeEntity.Type.EMPTY
)
That's it!
Conclusion:
To save a sealed class to Room or SQL, whether as an Entity, or as an Embedded object, you need to have one big data class with all the properties, from all the sealed variants, and use an Enum type to indicate variant type to use later for conversion between domain and data, or for indication in your code if you don't use Clean Architecture. Hard, but solid and flexible. I hope Room will have some annotations that can generate such code to get rid of the boilerplate code.
PS: This class is taken from Telegram's scheme, they also solve the problem of polymorphism when it comes to communication with a server. Checkout their TL Language here: https://core.telegram.org/mtproto/TL
PS2: If you like Telegram's TL language, you can use this generator to generate Kotlin classes from scheme.tl files: https://github.com/tamimattafi/mtproto
EDIT: You can use this code generating library to automatically generate Dao for compound classes, to make it easier to insert, which removes a lot of boilerplate to map things correctly.
Link: https://github.com/tamimattafi/android-room-compound
Happy Coding!

In my case I did the following:
sealed class Status2() {
object Online : Status2()
object Offline : Status2()
override fun toString(): String {
return when (this) {
is Online ->"Online"
is Offline -> "Offline"
}
}
}
class StatusConverter{
#TypeConverter
fun toHealth(value: Boolean): Status2 {
return if (value){
Status2.Online
} else{
Status2.Offline
}
}
#TypeConverter
fun fromHealth(value: Status2):Boolean {
return when(value){
is Status2.Offline -> false
is Status2.Online -> true
}
}
}
#Dao
interface CourierDao2 {
#Insert(onConflict = OnConflictStrategy.REPLACE)
suspend fun insertStatus(courier: CourierCurrentStatus)
#Query("SELECT * FROM CourierCurrentStatus")
fun getCourierStatus(): Flow<CourierCurrentStatus>
}
#Entity
data class CourierCurrentStatus(
#PrimaryKey
val id: Int = 0,
var status: Status2 = Status2.Offline
)
and it works like a charm

Cannot figure out how to save this field into database, save a list of Integer

I have this entity :
#Entity(tableName = "recipes")
data class Recipe(
#PrimaryKey val id: Int,
val name: String,
#TypeConverters(Converters::class)
val categories: List<Int>,
val picture: String,
#Embedded(prefix = "time")
val time: Time,
val people: Int,
val difficulty: Int,
val price: Int,
#Embedded(prefix = "ingredients")
#TypeConverters(Converters::class)
val ingredients: List<Ingredient>,
#Embedded(prefix = "utensils")
#TypeConverters(Converters::class)
val utensils: List<Utensil>,
#Embedded(prefix = "steps")
#TypeConverters(Converters::class)
val steps: List<Step>,
val createdAt: String,
val updatedAt: String
) : Serializable
And when I compile it, I got
Cannot figure out how to save this field into database. You can consider adding a type converter for it.
private final java.util.List<java.lang.Integer> categories = null;
Problem is, I added the TypeConverter, it's in my class Converters :
#TypeConverter
fun fromIntList(value: List<Int>): String {
val gson = Gson()
val type = object : TypeToken<List<Int>>() {}.type
return gson.toJson(value, type)
}
#TypeConverter
fun toIntList(value: String): List<Int> {
val gson = Gson()
val type = object : TypeToken<List<Int>>() {}.type
return gson.fromJson(value, type)
}
It should work since it knows that it should transforma list of Int to strings.
Futhermore, I got this error which I dont know where it can come from, and I have it like 5 times.
Entities and Pojos must have a usable public constructor. You can have an empty
constructor or a constructor whose parameters match the fields (by name and type).
I added the nested class like Ingredient, Step, Ustensil but I dont post the code since it should not be related.