I have a data class which extends another abstract class.
data class Savings(
val amount: BigDecimal? = null
) : Account()
abstract class Account(
val accountNumber: BigDecimal? = null
)
val saving: Savings = Savings(amount = BigDecimal.ONE)
How can I set the value for accountNumber property as that is not available in constructor. What other way I can set the value of the field?
You can make the property open in the superclass so you can override it in the data class constructor:
data class Savings(
val amount: BigDecimal? = null,
override val accountNumber: BigDecimal?
) : Account()
abstract class Account(
open val accountNumber: BigDecimal? = null
)
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))
}
I have a class ExpenseDto
data class ExpenseDto(
val id: Int,
val name: String,
val aggregationA: ExpenseAggregationA,
val aggregationB: ExpenseAggregationB,
val aggregationC: ExpenseAggregationC,
)
And all its associations have the same fields. And what are the best practies that can be applied here to universalize it
data class ExpenseAggregationA(
val id: Int,
val text: String? = null
)
data class ExpenseAggregationB(
val id: Int,
val text: String? = null
)
data class ExpenseAggregationC(
val id: Int,
val text: String? = null
)
data classes can inherit from a sealed class.
sealed class ExpenseAggParent (val id: Int, val text: String? = null) {
data class ExpAggA( override val id: Int, override ...)
data class ...
data class ...
}
Besides that, sometimes I like to have "property unifier" interfaces, especially when refactoring a legacy code with classes with the same semantics but different names of the properties:
interface HasId(val id: Int)
data class ExpenseAggregationX(
override val id: Int,
...
): HasId
data class ExpenseAggregationY: HasId {
val someOtherNameButStillId: Int
override val id: Int
get() = this.someOtherNameButStillId
}
And, of course, you can use the good old interface, but for that, you may re-use the above approach:
interface ExpenseAggregation: HasId, HasText
data class ExpenseAggregationA(
override val id: Int,
...
): ExpenseAggregation
// Other approach for classes with other existing names, see above
data class ExpenseAggregationB: ExpenseAggregation {
...
}
This is close to a mix-in approach which Kotlin does not currently support directly, but for completeness, there are delegations usable if your class is rather a service than a DTO.
I have a data class in Kotlin - where there are 5-6 fields,
data class DataClass(
val attribute1: String?,
val attribute2: String?,
val attribute3: Boolean?
)
i can initialise the class with DataClass(attribute1="ok", attribute2=null, attribute3= null)
Is there any way to prevent null values in data class ?
Kotlin's type system uses ? to declare nullability. Your data class has fields which are nullable. You can prevent them from being null by removing the ? from their types:
data class DataClass(
val attribute1: String, // not `String?`
val attribute2: String, // not `String?`
val attribute3: Boolean // not `Boolean?`
)
fun main() {
// This line will compile
val tmp = DataClass(attribute1 = "", attribute2 = "", attribute3 = false)
// This line will not compile
val fail = DataClass(attribute1 = null, attribute2 = null, attribute3 = null)
}
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 the following abstract class:
abstract class AbstractBook {
abstract val type: String
abstract val privateData: Any
abstract val publicData: Any
}
and the following class which inherits the AbstactBook class:
data class FantasyBook (
override val type: String = "FANTASY",
override val privateData: FantasyBookPrivateData,
override val publicData: FantasyBookPublicData
) : AbstractBook()
And then there is this class which should include data from any type of AbstractBook:
data class BookState(
val owner: String,
val bookData: AbstractBook,
val status: String
)
If I have an instance of BookState, how do I check which type of Book it is and then access the according FantasyBookPrivateData, and FantasyBookPublicData variables?
I hope I described my issue well & thanks in advance for any help!
What you describe is a sealed class:
sealed class Book<T, K> {
abstract val type: String
abstract val privateData: T
abstract val publicData: K
data class FantasyBook(
override val type: String = "FANTASY",
override val privateData: String,
override val publicData: Int) : Book<String, Int>()
}
and in your data class you can do pattern matching like this:
data class BookState(
val owner: String,
val bookData: Book<out Any, out Any>,
val status: String) {
init {
when(bookData) {
is Book.FantasyBook -> {
val privateData: String = bookData.privateData
}
}
}
}
to access your data in a type-safe manner. This solution also makes type redundant since you have that information in the class itself.
I agree with #Marko Topolnik that this seems like a code smell, so you might want to rethink your design.
interface AbstractBook<T , U> {
val privateData: T
val publicData: U
}
data class FantasyBook (
override val privateData: FantasyBookPrivateData,
override val publicData: FantasyBookPublicData
) : AbstractBook<FantasyBookPrivateData , FantasyBookPublicData>
data class BookState(
val owner: String,
val bookData: AbstractBook<*, *>,
val status: String
)
if(bookState.bookData is FantasyBook) {
// Do stuff
}
Creating a type variable is a weak type language writing style. You should use generic class.