I'm fetching json that has a 'type' field that contains a string, and I want to store this in my model object as an Enum with a string value.
The API I'm working with doesn't return all the information in one fetch, so once I have all the data I call my setProperties method.
All of my primitives are stored correctly in memory & my room db, but my Type class isn't converted. Any idea whats wrong with my type converter?
// Enum
enum class Type(var value: String) {
ARTICLE("article"),
COMMENT("comment"),
UNKNOWN("unknown")
}
// data class
data class FeedItem(#PrimaryKey override var id: Int) : Item(id) {
#TypeConverters(TypeConverter::class)
var type: Type? = Type.UNKNOWN
// other props...
fun setProperties(itemToCopy: FeedItem) {
this.type = itemToCopy.type
// set other props
}
}
// TypeConverter
class TypeConverter {
#TypeConverter
fun toString(type: Type?): String? {
return type?.value
}
#TypeConverter
fun toType(value: String?): Type? {
return when(value) {
Type.ARTICLE.value ->Type.ARTICLE
Type.COMMENT.value -> Type.COMMENT
else -> Type.UNKNOWN
}
}
}
Related
I have an enum class which maps language locale to a list.
How can I fix the function getReservationFrequencies inside the companion object
to return the value of the map based on the locale (key)?
enum class ReservationFrequencies(val frequencies: Map<Language, List<ReservationFrequency>>) {
APPLICATION(mapOf(
Language.en to listOf(
ReservationFrequency(0,"once",0),
ReservationFrequency(1,"Monthly",2),
ReservationFrequency(2,"Quarterly",5),
ReservationFrequency(3,"Semi-annually",5),
ReservationFrequency(4,"Annually",5)
),
Language.ar to listOf(
ReservationFrequency(0,"مرة واحده",0),
ReservationFrequency(1,"شهرياً",2),
ReservationFrequency(2,"ربع سنوياً",5),
ReservationFrequency(3,"نصف سنوياً",5),
ReservationFrequency(4," سنوياً",5)
)
));
}
I tried creating a companion object that includes a function that returns the list
companion object {
fun getReservationFrequencies(locale: String?) : List<ReservationFrequency> {
val reservationFrequencyDtos = mutableListOf<ReservationFrequency>()
reservationFrequencies.values()
.filter { locale!!.contains(it.name)}
.forEach() {
ReservationFrequency.add(ReservationFrequency(code = it.frequencies))
}
}
}
I'm expecting a List<ReservationFrequency> based on the locale
Probably just this
fun getReservationFrequencies(locale: String?) : List<ReservationFrequency> =
ReservationFrequencies.APPLICATION.frequencies.filter {
it.key.name == locale // I don't know the specifics of how to match the String locale arg against Language
}.map {
it.value
}.first()
This question already has an answer here:
kotlinx deserialization: different types && scalar && arrays
(1 answer)
Closed 7 months ago.
With a structure similar to the following:
#Serializable
sealed class Parameters
#Serializable
data class StringContainer(val value: String): Parameters()
#Serializable
data class IntContainer(val value: Int): Parameters()
#Serializable
data class MapContainer(val value: Map<String, Parameters>): Parameters()
// more such as list, bool and other fairly (in the context) straight forward types
And the following container class:
#Serializable
data class PluginConfiguration(
// other value
val parameters: Parameters.MapContainer,
)
I want to reach a (de)serialization where the paramters are configured as a flexible json (or other) map, as one would usually expect:
{
"parameters": {
"key1": "String value",
"key2": 12,
"key3": {}
}
}
And so on. Effectively creating a flexible structure that is still structured enough to not be completely uncontrolled as Any would be. There's a fairly clearly defined (de)serialization, but I cannot figure how to do this.
I've tried reading the following
https://github.com/Kotlin/kotlinx.serialization/blob/master/docs/serialization-guide.md
And I do have a hunch that a polymorphic serializer is needed, but so far I'm bumping in to either generic structures, which I believe is way overkill for my purpose or that it for some reason cannot find the serializer for my subclasses, when writing a custom serializer for Parameters.
Update
So using custom serializers combined with surrogate classes, most things are working. The current problem is when values are put into the map, I get a kotlin.IllegalStateException: Primitives cannot be serialized polymorphically with 'type' parameter. You can use 'JsonBuilder.useArrayPolymorphism' instead. Even when I enable array polymorphism this error arises
The answer with kotlinx deserialization: different types && scalar && arrays is basically the answer, and the one I will accept. However, for future use, the complete code to my solution is as follows:
Class hierarchy
#kotlinx.serialization.Serializable(with = ParametersSerializer::class)
sealed interface Parameters
#kotlinx.serialization.Serializable(with = IntContainerSerializer::class)
data class IntContainer(
val value: Int
) : Parameters
#kotlinx.serialization.Serializable(with = StringContainerSerializer::class)
data class StringContainer(
val value: String
) : Parameters
#kotlinx.serialization.Serializable(with = MapContainerSerializer::class)
data class MapContainer(
val value: Map<String, Parameters>
) : Parameters
#kotlinx.serialization.Serializable
data class PluginConfiguration(
val plugin: String,
val parameters: MenuRunnerTest.MapContainer
)
Serializers:
abstract class BaseParametersSerializer<T : Parameters> : KSerializer<T> {
override val descriptor: SerialDescriptor = JsonElement.serializer().descriptor
override fun serialize(encoder: Encoder, value: T) {
fun toJsonElement(value: Parameters): JsonElement = when (value) {
is IntContainer -> JsonPrimitive(value.value)
is MapContainer -> JsonObject(
value.value.mapValues { toJsonElement(it.value) }
)
is StringContainer -> JsonPrimitive(value.value)
}
val sur = toJsonElement(value)
encoder.encodeSerializableValue(JsonElement.serializer(), sur)
}
override fun deserialize(decoder: Decoder): T {
with(decoder as JsonDecoder) {
val jsonElement = decodeJsonElement()
return deserializeJson(jsonElement)
}
}
abstract fun deserializeJson(jsonElement: JsonElement): T
}
object ParametersSerializer : BaseParametersSerializer<Parameters>() {
override fun deserializeJson(jsonElement: JsonElement): Parameters {
return when(jsonElement) {
is JsonPrimitive -> when {
jsonElement.isString -> StringContainerSerializer.deserializeJson(jsonElement)
else -> IntContainerSerializer.deserializeJson(jsonElement)
}
is JsonObject -> MapContainerSerializer.deserializeJson(jsonElement)
else -> throw IllegalArgumentException("Only ints, strings and strings are allowed here")
}
}
}
object StringContainerSerializer : BaseParametersSerializer<StringContainer>() {
override fun deserializeJson(jsonElement: JsonElement): StringContainer {
return when(jsonElement) {
is JsonPrimitive -> StringContainer(jsonElement.content)
else -> throw IllegalArgumentException("Only strings are allowed here")
}
}
}
object IntContainerSerializer : BaseParametersSerializer<IntContainer>() {
override fun deserializeJson(jsonElement: JsonElement): IntContainer {
return when (jsonElement) {
is JsonPrimitive -> IntContainer(jsonElement.int)
else -> throw IllegalArgumentException("Only ints are allowed here")
}
}
}
object MapContainerSerializer : BaseParametersSerializer<MapContainer>() {
override fun deserializeJson(jsonElement: JsonElement): MapContainer {
return when (jsonElement) {
is JsonObject -> MapContainer(jsonElement.mapValues { ParametersSerializer.deserializeJson(it.value) })
else -> throw IllegalArgumentException("Only maps are allowed here")
}
}
}
This structure should be expandable for lists, doubles and other structures, not included in the example :)
I'm trying to build a class where certain values are Observable but also Serializable.
This obviously works and the serialization works, but it's very boilerplate-heavy having to add a setter for every single field and manually having to call change(...) inside each setter:
interface Observable {
fun change(message: String) {
println("changing $message")
}
}
#Serializable
class BlahVO : Observable {
var value2: String = ""
set(value) {
field = value
change("value2")
}
fun toJson(): String {
return Json.encodeToString(serializer(), this)
}
}
println(BlahVO().apply { value2 = "test2" })
correctly outputs
changing value2
{"value2":"test2"}
I've tried introducing Delegates:
interface Observable {
fun change(message: String) {
println("changing $message")
}
#Suppress("ClassName")
class default<T>(defaultValue: T) {
private var value: T = defaultValue
operator fun getValue(observable: Observable, property: KProperty<*>): T {
return value
}
operator fun setValue(observable: Observable, property: KProperty<*>, value: T) {
this.value = value
observable.change(property.name)
}
}
}
#Serializable
class BlahVO : Observable {
var value1: String by Observable.default("value1")
fun toJson(): String {
return Json.encodeToString(serializer(), this)
}
}
println(BlahVO().apply { value1 = "test1" }) correctly triggers change detection, but it doesn't serialize:
changing value1
{}
If I go from Observable to ReadWriteProperty,
interface Observable {
fun change(message: String) {
println("changing $message")
}
fun <T> look(defaultValue: T): ReadWriteProperty<Observable, T> {
return OP(defaultValue, this)
}
class OP<T>(defaultValue: T, val observable: Observable) : ObservableProperty<T>(defaultValue) {
override fun setValue(thisRef: Any?, property: KProperty<*>, value: T) {
super.setValue(thisRef, property, value)
observable.change("blah!")
}
}
}
#Serializable
class BlahVO : Observable {
var value3: String by this.look("value3")
fun toJson(): String {
return Json.encodeToString(serializer(), this)
}
}
the result is the same:
changing blah!
{}
Similarly for Delegates.vetoable
var value4: String by Delegates.vetoable("value4", {
property: KProperty<*>, oldstring: String, newString: String ->
this.change(property.name)
true
})
outputs:
changing value4
{}
Delegates just doesn't seem to work with Kotlin Serialization
What other options are there to observe a property's changes without breaking its serialization that will also work on other platforms (KotlinJS, KotlinJVM, Android, ...)?
Serialization and Deserialization of Kotlin Delegates is not supported by kotlinx.serialization as of now.
There is an open issue #1578 on GitHub regarding this feature.
According to the issue you can create an intermediate data-transfer object, which gets serialized instead of the original object. Also you could write a custom serializer to support the serialization of Kotlin Delegates, which seems to be even more boilerplate, then writing custom getters and setters, as proposed in the question.
Data Transfer Object
By mapping your original object to a simple data transfer object without delegates, you can utilize the default serialization mechanisms.
This also has the nice side effect to cleanse your data model classes from framework specific annotations, such as #Serializable.
class DataModel {
var observedProperty: String by Delegates.observable("initial") { property, before, after ->
println("""Hey, I changed "${property.name}" from "$before" to "$after"!""")
}
fun toJson(): String {
return Json.encodeToString(serializer(), this.toDto())
}
}
fun DataModel.toDto() = DataTransferObject(observedProperty)
#Serializable
class DataTransferObject(val observedProperty: String)
fun main() {
val data = DataModel()
println(data.toJson())
data.observedProperty = "changed"
println(data.toJson())
}
This yields the following result:
{"observedProperty":"initial"}
Hey, I changed "observedProperty" from "initial" to "changed"!
{"observedProperty":"changed"}
Custom data type
If changing the data type is an option, you could write a wrapping class which gets (de)serialized transparently. Something along the lines of the following might work.
#Serializable
class ClassWithMonitoredString(val monitoredProperty: MonitoredString) {
fun toJson(): String {
return Json.encodeToString(serializer(), this)
}
}
fun main() {
val monitoredString = obs("obsDefault") { before, after ->
println("""I changed from "$before" to "$after"!""")
}
val data = ClassWithMonitoredString(monitoredString)
println(data.toJson())
data.monitoredProperty.value = "obsChanged"
println(data.toJson())
}
Which yields the following result:
{"monitoredProperty":"obsDefault"}
I changed from "obsDefault" to "obsChanged"!
{"monitoredProperty":"obsChanged"}
You however lose information about which property changed, as you don't have easy access to the field name. Also you have to change your data structures, as mentioned above and might not be desirable or even possible. In addition, this work only for Strings for now, even though one might make it more generic though.
Also, this requires a lot of boilerplate to start with. On the call site however, you just have to wrap the actual value in an call to obs.
I used the following boilerplate to get it to work.
typealias OnChange = (before: String, after: String) -> Unit
#Serializable(with = MonitoredStringSerializer::class)
class MonitoredString(initialValue: String, var onChange: OnChange?) {
var value: String = initialValue
set(value) {
onChange?.invoke(field, value)
field = value
}
}
fun obs(value: String, onChange: OnChange? = null) = MonitoredString(value, onChange)
object MonitoredStringSerializer : KSerializer<MonitoredString> {
override val descriptor: SerialDescriptor = PrimitiveSerialDescriptor("MonitoredString", PrimitiveKind.STRING)
override fun serialize(encoder: Encoder, value: MonitoredString) {
encoder.encodeString(value.value)
}
override fun deserialize(decoder: Decoder): MonitoredString {
return MonitoredString(decoder.decodeString(), null)
}
}
i have custom jackson configuration in kotlin:
#Configuration
class JacksonConfiguration {
#Bean
fun objectMapper(): com.fasterxml.jackson.databind.ObjectMapper = jacksonObjectMapper()
.setSerializationInclusion(JsonInclude.Include.NON_EMPTY)
.apply {
registerModules(customJavaTimeModule(), KotlinModule())
configure(DeserializationFeature.FAIL_ON_UNKNOWN_PROPERTIES, false)
}
}
private fun customJavaTimeModule() = JavaTimeModule().apply {
addSerializer(String::class.java, StringSerializerTypeHandler())
}
private class StringSerializerTypeHandler : JsonSerializer<String?>() {
#Throws(IOException::class, JsonProcessingException::class)
override fun serialize(value: String?, jgen: JsonGenerator?, provider: SerializerProvider?) {
var outputValue: String = value.toString()
if (!value.isNullOrEmpty()) {
// logic for changing the string - removing diacritics
jgen?.writeString(outputValue)
} else {
//provider?. // what here?
// jgen?.writeString(value)
// dont serialize the field at all - just skip it
}
}
}
What's important is that i do not want that field to be serialized at all when the field value is null or empty.
I can not get rid of else block - then I will have error:
Can not write a field name, expecting a value
I want to set this logic globally.
Solution 1:
I had to override this method:
override fun isEmpty(provider: SerializerProvider?, value: String?): Boolean {
return value.isNullOrEmpty()
}
Then i can get rid of else block.
I'm new to Kotlin, so I have this interface.
interface User {
var nickName : String
}
Now I want to create a class PrivateUser that implements this interface. I have also to implement the abstract member nickName.
Via constructor it's very simple
class PrivateUser(override var nickName: String) : User
However when I try to implement member inside the class Idea generates me this code
class Button: User {
override var nickName: String
get() = TODO("not implemented")
set(value) {}
}
It's confusing to me how to implement it further.
Properties must be initialized in Kotlin. When you declare the property in the constructor, it gets initialized with whatever you pass in. If you declare it in the body, you need to define it yourself, either with a default value, or parsed from other properties.
Some examples:
class Button : User {
override var nickname = "Fred"
}
class Button(val firstName: String, val lastName: String) : User {
override var nickname = "${firstname[0]}$lastname"
}
The code generated by IDEA is useful if you want a non-default getter and/or setter, or if you want a property without a backing field (it's getter and setter calculate on the fly when accessed).
More examples:
class Button : User {
override var nickname = "Fred"
get() = if (field.isEmpty()) "N/A" else field
set(value) {
// No Tommy
field = if (value == "Tommy") "" else value
}
}
class Button(val number: Int) : User {
var id = "$number"
private set
override var nickname: String
get() {
val parts = id.split('-')
return if (parts.size > 1) parts[0] else ""
}
set(value) {
field = if (value.isEmpty()) "$number" else "$value-$number"
}
}