I have a redis entity using a kotlin data class and its Id should be a combination of few other fields from the same class.
Can this be achieved by defining setter for Id field instead of computing it outside of data class?
#RedisHash("Game")
data class Game(
#Id
val generatedId: String = "Default_ID",
val name: String,
val location: String,
val homeTeam: String,
val awayTeam: String
)
// want something like this
var generatedId : String = "DEFAULT_ID"
get() = "${name}${location}"
// or even better
var generated_Id : String = "${name}${location}"
Did you try to do something like this?
#RedisHash("Game")
data class Game(
val name: String,
val location: String,
val homeTeam: String,
val awayTeam: String,
#Id
val generatedId: String = "${name}${location}"
)
Related
I was wondering if there is any way to refer to a previously defined property in a constructor in Kotlin. Something like:
data class Order(
val id: String,
val transformedId: String
}
and then when initiating the class, do:
val orderId = getOrderId()
Order(
id = orderId,
transformedId = transform(id)
}
You can do this with a secondary constructor.
data class Order(
val id: String,
val transformedId: String
) {
constructor(id: String): this(id, transform(id))
}
If you want this to be the only way to create the class, you can make the primary constructor private:
data class Order private constructor(
val id: String,
val transformedId: String
) {
constructor(id: String): this(id, transform(id))
}
My use case:
I have a large number of POJO models that are different types of requests for a third-party API. All of them have several common fields and a couple unique ones.
I was hoping to build something that conceptually looks like this
class RequestBase(
val commonField1: String,
val commonField2: String,
...
val commonFieldX: String
)
class RequestA(
val uniqueFieldA: String
): RequestBase()
class RequestB(
val uniqueFieldB: String
): RequestBase()
fun main() {
val requestA = RequestA(
commonField1 = "1",
commonField2 = "2",
...
uniqueFieldA = "A"
)
}
I can of course override the common fields in every child request and then pass them to the parent constructor, but this ends up producing a lot of boilerplate code and bloats the model. Are there any options I can explore here?
Notice that what you are doing in the parentheses that follow a class declaration is not "declaring what properties this class has", but "declaring the parameters of this class' primary constructor". The former is just something you can do "along the way", by adding var or val.
Each class can have its own primary constructor that take any number and types of parameters that it likes, regardless of what class its superclass is. Therefore, it is not unreasonable to have to specify all the parameters of the constructor:
open class RequestBase(
val commonField1: String,
val commonField2: String,
...
val commonFieldX: String
)
class RequestA(
// notice that the parameters for the inherited properties don't have the
// "val" prefix, because you are not declaring them in the subclass again.
// These are just constructor parameters.
commonField1: String,
commonField2: String,
...
commonFieldX: String,
val uniqueFieldA: String,
): RequestBase(
commonField1,
commonField2,
...
commonFieldX,
)
If you find this unpleasant, there are a bunch of ways to work around this.
One way is to use composition and delegation - create an interface having the common properties. The specific requests' primary constructors will take a RequestBase and their unique properties, and implement the interface by delegating to the RequestBase:
interface Request {
val commonField1: String
val commonField2: String
val commonFieldX: String
}
open class RequestBase(
override val commonField1: String,
override val commonField2: String,
override val commonFieldX: String
): Request
class RequestA(
val requestBase: RequestBase,
val uniqueField: String
): Request by requestBase
This allows you to access someRequestA.commonFieldX directly, without doing someRequestA.requestBase.commonFieldX, but to create a RequestA, you need to create a RequestBase first:
RequestA(
RequestBase(...),
uniqueField = ...
)
Another way is to change your properties to vars, give them default values, and move them out of the constructor parameters:
open class RequestBase {
var commonField1: String = ""
var commonField2: String = ""
var commonFieldX: String = ""
}
class RequestA: RequestBase() {
var uniqueField: String = ""
}
Then to create an instance of RequestA, you would just call its parameterless constructor, and do an apply { ... } block:
RequestA().apply {
commonField1 = "foo"
commonField2 = "bar"
commonFieldX = "baz"
uniqueField = "boo"
}
The downside of this is of course that the properties are all mutable, and you have to think of a default value for every property. You might have to change some properties to nullable because of this, which might not be desirable.
You can't do it with constructors of base class. Without constructors it's possible:
open class RequestBase {
lateinit var commonField1: String
lateinit var commonField2: String
...
lateinit var commonFieldX: String
}
class RequestA(
val uniqueFieldA: String
): RequestBase()
class RequestB(
val uniqueFieldB: String
): RequestBase()
fun main() {
val requestA = RequestA(
uniqueFieldA = "A"
).apply {
commonField1 = "1"
commonField2 = "2"
...
commonFieldX = "X"
}
}
I'm trying to use a resource string inside a companion object that is inside a data class. but I don't Know how to obtain context in that case in Kotlin.
Anyone knows how to do it?
data class PhoneCall(
val type: String,
val code: String,
val description: String){
companion object{
const val SOLUTION_NO_SOLUTION = "NO_SOLUTION"
const val SOLUTION_TOMORROW = "71_INAT"
const val SOLUTION_TODAY = "72_INAT"
val solutions = listOf(
PhoneCall(Service.Traffic.PICK_UP, SOLUTION_NO_SOLUTION, Resources.getSystem().getString(R.string.makeService))
)
}
I need to use a resource string in the 3 parameter, but I'm not able to get the context.
You can modify you PhoneCall model to store a string resource id instead of the actual string.
data class PhoneCall(
val type: String,
val code: String,
#StringRes val description: Int
) {
companion object {
const val SOLUTION_NO_SOLUTION = "NO_SOLUTION"
const val SOLUTION_TOMORROW = "71_INAT"
const val SOLUTION_TODAY = "72_INAT"
val solutions = listOf(
PhoneCall(Service.Traffic.PICK_UP, SOLUTION_NO_SOLUTION, R.string.makeService)
)
}
}
Then, when you need to display this data in the UI (say a TextView), you can fetch the string from the resource id.
descriptionTextView.text = getString(phoneCall.description)
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)