I often will create a data class in Kotlin that is used internally for data models. Example:
data class MyDataModel(
var id: String? = null,
var ownerId: String,
var name: String,
var isPrivate: Boolean = false,
)
I often need to serialize these classes to JSON. The problem is that some of the class properties are not nullable and there are cases where I need to exclude those fields in the serialization. I haven't found a clean and simple way to do that. The solution I currently use is not to use non-nullable properties and then set those that I don't want serialized to null.
Is there another approach?
Solution using kotlinx.serialization:
Define class, including all fields you want to be serialized, mark it as #Serializable
#Serializable
open class MyDataModelSerializable(
open var id: String? = null
)
Make your data class to be its subtype:
data class MyDataModel(
var ownerId: String,
var name: String,
var isPrivate: Boolean = false,
override var id: String? = null
) : MyDataModelSerializable(id)
Serialize instances of MyDataModel class with serializer for MyDataModelSerializable:
val s = serializer<MyDataModelSerializable>()
println(Json.encodeToString(s, MyDataModel(ownerId = "1", name = "2", id = "3", isPrivate = true))) //{"id":"3"}
println(Json.encodeToString(s, MyDataModel(ownerId = "1", name = "2", isPrivate = true))) //{}
println(Json{encodeDefaults = true}.encodeToString(s, MyDataModel(ownerId = "1", name = "2"))) //{"id":null}
Related
Is there a syntactic sugar in Kotlin to iterate on each field/property value of a data class?
Sample:
data class User(
var firstName: String = DEFAULT_VALUE_STRING,
var middleName: String = DEFAULT_VALUE_STRING,
var lastName: String = DEFAULT_VALUE_STRING
)
val user = User()
Then check if any of the property's value is empty, considering all of it is String data type with something like this
if (user.properties.any{ it.isBlank() }) {
// TODO ...
}
Probably the closest you'll get is checking all the values of all the generated componentX() functions (since they're only created for the constructor parameter properties, the "data" in a data class) but yeah that involves reflection.
If I were you, I'd create an interface with a properties property and make all your data classes implement that - something like this:
import kotlin.reflect.KProperty0
interface HasStringProperties {
val properties: List<KProperty0<String>>
}
data class User(
var firstName: String = "",
var middleName: String = "",
var lastName: String = ""
) : HasStringProperties {
override val properties = listOf(::firstName, ::middleName, ::lastName)
}
fun main() {
val user = User("Funny", "", "Name")
println(user.properties.any {it.get().isBlank()})
}
So no, it's not automatic - but specifying which properties you want to include is simple, and required if you're going to access it on a particular class, so there's an element of safety there.
Also, because you're explicitly specifying String properties, there's type safety included as well. Your example code is implicitly assuming all properties on your data classes will be Strings (or at least, they're a type with an isBlank() function) which isn't necessarily going to be true. You'd have to write type-checking into your reflection code - if you say "I don't need to, the classes will only have String parameters" then maybe that's true, until it isn't. And then the reflection code has to be written just because you want to add a single age field or whatever.
You don't actually have to use property references in Kotlin either, you could just grab the current values:
interface HasStringProperties {
val properties: List<String>
}
data class User(
var firstName: String = "",
var middleName: String = "",
var lastName: String = ""
) : HasStringProperties {
// getter function creating a new list of current values every time it's accessed
override val properties get() = listOf(firstName, middleName, lastName)
}
fun main() {
val user = User("Funny", "", "Name")
println(user.properties.any {it.isBlank()})
}
It depends whether you want to be able to reference the actual properties on the class itself, or delegate to a getter to fetch the current values.
And of course you could use generics if you want, list all the properties and use filterIsInstance<String> to pull all the strings. And you could put a function in the interface to handle a generic isEmpty check for different types. Put all the "check these properties aren't 'empty'" code in one place, so callers don't need to concern themselves with working that out and what it means for each property
How can I create an instance of InfoA that contains also title. Do I need to modify the classes?
Can't specify the title.
Also, do I need to create setters for it? To not access with the _
val info = InfoA(_subtitle = "SUBTITLE", title = ...)
open class Info(
open val action: Action = Action(),
open val title: String? = ""
) {
fun hasAction(): Boolean = action.hasAction()
}
class InfoA(
private val _subtitle: String? = "",
private val _image: String? = "",
private val _backgroundImage: String? = "",
private val _backgroundColor: String? = null,
private val _foregroundColor: String? = null,
private val _borderColor: String? = null
) : Info() {
val subtitle: String
get() = _subtitle.orEmpty()
val image: String
get() = _image.orEmpty()
val backgroundImage: String
get() = _backgroundImage.orEmpty()
val backgroundColor: Int?
get() = if (_backgroundColor != null) convertRgbStringToColorInt(_backgroundColor) else null
val foregroundColor: Int?
get() = if (_foregroundColor != null) convertRgbStringToColorInt(_foregroundColor) else null
val borderColor: Int?
get() = if (_borderColor != null) convertRgbStringToColorInt(_borderColor) else null
}
As the code is written, title is a val, so it can't be changed from its initial value — which is empty string if (as in the case of InfoA) something calls its constructor without specifying another value.
If it were changed to be a var, then it could be changed later, e.g.:
val info = InfoA(_subtitle = "SUBTITLE").apply{ title = "..." }
Alternatively, if you want to keep it a val, then InfoA would need to be changed: the most obvious way would be to add a title parameter in its constructor, and pass that up to Info:
class InfoA(
title: String? = "",
// …other fields…
) : Info(title = title) {
Note that this way, InfoA can never use Info's default value for title, so you may need to duplicate that default in InfoA's constructor.
The need to duplicate superclass properties in a subclass constructor is awkward, but there's currently no good way around it. (See e.g. this question.) If there are many parameters, you might consider bundling them together into a single data class, which could then be passed easily up to the superclass constructor — but of course users of the class would need to specify that. (Some people think that having more than a few parameters is a code smell, and that bundling them together can often improve the design.)
I have a project with Kotlin and Springboot.
In this project an entity have this following fields: id, name and parent.
What i want is to only get the id and the name. So i made a projection interface view for that entity.
This is my entity:
#Entity
data class Keyword(
#Id
#GeneratedValue(generator = "uuid2")
#GenericGenerator(name = "uuid2", strategy = "uuid2")
#Column(columnDefinition = "BINARY(16)")
var id: UUID? = null,
#Column(columnDefinition = "BINARY(16)")
var parent: UUID? = null,
#NotBlank
var name: String? = null
)
Repository:
#Repository
interface KeywordRepository: JpaRepository<Keyword, UUID> {
#Query(value = "SELECT keyword.id, keyword.parent, keyword.name FROM keyword LEFT JOIN project_keyword ON project_keyword.keyword_id = keyword.id WHERE project_keyword.project_id LIKE :id", nativeQuery = true)
fun findAllKeywordsByProjectId(id: UUID): MutableList<KeyWordView>
}
Service:
#Service
class KeywordService (
private val projectService: ProjectService,
private val keywordRepository: KeywordRepository
) {
fun getKeywordsByProjectId(id: UUID): MutableList<KeyWordView> {
projectService.checkIfProjectExistsById(id)
return keywordRepository.findAllKeywordsByProjectId(id).toMutableList()
}
}
My projection interface class:
interface KeyWordView {
val id: UUID
val name: String?
}
When i call this endpoint via controller class. I get this output:
"list": [
{
"name": "MARINE MICROBIOTA",
"id": "0,31,-36,77,29,123,66,-25,-127,-43,-31,83,104,-90,47,10"
}
]
But if i change the val id: String to val id: UUID in my KeywordView interface, i get this following error:
{
"code": 500,
"data": null,
"message": "Could not write JSON: Projection type must be an interface!; nested exception is com.fasterxml.jackson.databind.JsonMappingException: Projection type must be an interface! (through reference chain: no.inmeta.ris.util.response.ResponseDto[\"data\"]->no.inmeta.ris.util.pagination.PageDto[\"list\"]->java.util.ArrayList[0]->com.sun.proxy.$Proxy199[\"id\"])",
"status": "FAIL"
}
Anyone know how to solve this problem? I want to receive the UUID as UUID not with the strange format.
Thank you!
I guess the problem is the UUID Class. As your entity states you defined dir hibernate that the column in db is a binary(16). And i suppose using this UUID Type in the Interface projection does not Work since there is no valid mapping information (how to transform the data coming as binary with a length of 16 bytes to the UUID Class). So I assume you have to change the Type of your column or you have to use string and write a function to Transform that String.
Another possibility is to create a second entity for that table with Just the two cols you want. And Just use that second dao as your are using yiur projection.
I have the following data class in Kotlin:
import com.google.gson.annotations.SerializedName
data class RouteGroup(
#SerializedName("name") var name: String,
#SerializedName("id") var id: Int
)
Sometimes I need to create an object with both fields, sometimes with only one of them.
How can I do this?
EDIT
This is not the duplicate of this question: Can Kotlin data class have more than one constructor?
That question shows how to set a default value for a field. But in my case, I don't need to serialize the field with the default value. I want a field to be serialized only when I explicitly assign a value to it.
it is easy you have to use the nullable operator
import com.google.gson.annotations.SerializedName
data class RouteGroup #JvmOverloads constructor(
#SerializedName("name") var name: String? = null,
#SerializedName("id") var id: Int? = null
)
You may need something like this:
sealed class RouteGroup
data class RouteGroupWithName(
#SerializedName("name") var name: String
) : RouteGroup()
data class RouteGroupWithId(
#SerializedName("id") var id: Int
) : RouteGroup()
data class RouteGroupWithNameAndId(
#SerializedName("name") var name: String,
#SerializedName("id") var id: Int
) : RouteGroup()
EDIT 1:
Or you can use nullable fields and named parameters like this:
data class RouteGroup(
#SerializedName("name") var name: String? = null,
#SerializedName("id") var id: Int? = null
)
val routeGroupWithName = RouteGroup(name = "example")
val routeGroupWithId = RouteGroup(id = 2)
val routeGroupWithNameAndId = RouteGroup(id = 2, name = "example")
I have some JSON that looks like this:
{
"name" : "Credit Card",
"code" : "AUD",
"value" : 1000
}
and am using Moshi to unmarshall this into a data structure like:
data class Account(
#Json(name = "name")
val name: String,
#Json(name = "currency")
val currency: String,
#Json(name = "value")
val value: Int
)
Everything works well. However, I really would like to extract the currency and value parameters into a separate Money object. So my model looks more like:
data class Money(
#Json(name = "currency")
val currency: String,
#Json(name = "value")
val value: Int
)
data class Account(
#Json(name = "name")
val name: String,
#Json(name = "???")
val money: Money
)
The challenge I'm struggling with is how to annotate things so that the Money object can be given two different fields (currency and value) that come from the same level as the parent account.
Do I need to create an intermediate "unmarshalling" object called, say, MoshiAccount and then use a custom adapter to convert that to my real Account object?
I saw How to deseralize an int array into a custom class with Moshi? which looks close (except that in that case, the adapted object (VideoSize) only needs a single field as input... in my case, I need both currency and value)
Any thoughts or suggestions would be much appreciated. Thanks
Moshi's adapters can morph your JSON structure for you.
object ADAPTER {
private class FlatAccount(
val name: String,
val currency: String,
val value: Int
)
#FromJson private fun fromJson(json: FlatAccount): Account {
return Account(json.name, Money(json.currency, json.value))
}
#ToJson private fun toJson(account: Account): FlatAccount {
return FlatAccount(account.name, account.money.currency, account.money.value)
}
}
Don't forget to add the adapter to your Moshi instance.
val moshi = Moshi.Builder().add(Account.ADAPTER).add(KotlinJsonAdapterFactory()).build()
val adapter = moshi.adapter(Account::class.java)