I want to have following person object in Kotlin :
var p = person {
age = 22
gender = "male"
name {
first = "Ali"
last = "Rezaei"
}
}
I have following code to build it :
data class Person(var age: Int? = null, var gender: String? = null
, var name : Name? = null) {
}
fun name(init: Name.() -> Unit): Name {
val n = Name()
n.init()
return n
}
data class Name(var first: String? = null, var last : String? = null)
fun person(init: Person.() -> Unit): Person {
val p = Person()
p.init()
return p
}
But when I print it, the result is following :
Person(age=22, gender="male", name=null)
What is wrong with my code?
You could make name an extension function on Person that assigns the Name to the Person instead of returning it:
fun Person.name(init: Name.() -> Unit) {
val n = Name()
n.init()
this.name = n
}
You could even consider a more concise syntax for the same, like this:
fun Person.name(init: Name.() -> Unit) {
this.name = Name().apply(init)
}
Shameless plug for my repository discussing DSL design and containing examples.
You need to assign to name. This ended up working for me...
var p = person {
age = 22
gender = "male"
name = name {
first = "Ali"
last = "Rezaei"
}
}
Related
I have the following structure at present:
#Entity
#Table(name = "table_app_settings")
data class AppSetting(
#Id
#GeneratedValue(strategy = GenerationType.IDENTITY)
#Column(name = "app_setting_id")
val id: Long? = null,
#Column(name = "app_setting_name")
val name: String = "",
#Column(name = "app_setting_value")
var value: String = "",
#Column(name = "app_setting_type")
val type: AppSettingType,
)
enum class AppSettingType {
CHAR,
STRING,
BYTE,
SHORT,
INT,
LONG,
DOUBLE,
FLOAT,
BOOLEAN,
}
This is then saved to the database with the following:
override fun saveAppSetting(setting: AppSetting): DatabaseResult<AppSetting> {
log.info("Saving App Setting ${setting.name} to database.")
return try {
// Attempt to save the entity to the database. If we do not throw an exception, return success.
val savedSetting = appSettingsRepository.save(setting)
DatabaseResult(
code = ResultCode.CREATION_SUCCESS,
entity = savedSetting
)
} catch(exception: DataAccessException) {
log.error("Unable to save App Setting ${setting.name} to database. Reason: ${exception.message}")
DatabaseResult(
code = ResultCode.CREATION_FAILURE
)
}
}
Now, let's say that I wish to save a Char type to database, I figure I would use the following:
override fun saveAppSetting(name: String, value: Char): DatabaseResult<Char> {
val appSettingResult = saveAppSetting(AppSetting(
name = name,
value = value.toString(),
type = AppSettingType.CHAR,
))
return if(appSettingResult.code != ResultCode.CREATION_FAILURE) {
val entity = getAppSetting<Char>(appSettingResult.entity?.name!!).entity.toString().first()
DatabaseResult(
code = appSettingResult.code,
entity = entity
)
} else {
DatabaseResult(
code = ResultCode.CREATION_FAILURE,
)
}
}
I also figured that I would need to do the following in order to retrieve the correct object type:
override fun getAppSetting(name: String): DatabaseResult<Any?> {
log.info("Getting App Setting $name from database.")
val appSetting = appSettingsRepository.findAppSettingByName(name)
return if(appSetting != null) {
log.info("App Setting $name has ID of ${appSetting.id} within the database")
when(appSetting.type) {
AppSettingType.CHAR -> {
DatabaseResult<Char>(
code = ResultCode.FETCH_SUCCESS,
entity = appSetting.value.first(),
)
}
AppSettingType.STRING -> {
DatabaseResult<String>(
code = ResultCode.FETCH_SUCCESS,
entity = appSetting.value,
)
}
AppSettingType.BYTE -> {
DatabaseResult<Byte>(
code = ResultCode.FETCH_SUCCESS,
entity = appSetting.value.toByte(),
)
}
AppSettingType.SHORT -> {
DatabaseResult<Short>(
code = ResultCode.FETCH_SUCCESS,
entity = appSetting.value.toShort(),
)
}
AppSettingType.INT -> {
DatabaseResult<Int>(
code = ResultCode.FETCH_SUCCESS,
entity = appSetting.value.toInt(),
)
}
AppSettingType.LONG -> {
DatabaseResult<Long>(
code = ResultCode.FETCH_SUCCESS,
entity = appSetting.value.toLong(),
)
}
AppSettingType.DOUBLE -> {
DatabaseResult<Double>(
code = ResultCode.FETCH_SUCCESS,
entity = appSetting.value.toDouble(),
)
}
AppSettingType.FLOAT -> {
DatabaseResult<Float>(
code = ResultCode.FETCH_SUCCESS,
entity = appSetting.value.toFloat()
)
}
AppSettingType.BOOLEAN -> {
DatabaseResult<Boolean>(
code = ResultCode.FETCH_SUCCESS,
entity = appSetting.value.toBoolean()
)
}
}
} else {
log.error("App Setting $name does not seem to exist within the database.")
DatabaseResult(
code = ResultCode.FETCH_FAILURE
)
}
However, when I then wish to use said object, I still have to write something like the following:
val newBarcode = getAppSetting("barcode_value").entity.toString().toInt()
Assuming I've "initialised" barcode_value with a value of 177 (for example).
How can I get the function to return what I need without having to do .toString.to...()?
Yes this all possible, here is a simplified demo, firstly
import kotlin.reflect.KClass
data class AppSetting(
val id: Long? = null,
val name: String = "",
var value: String = "",
val type: AppSettingType,
)
enum class AppSettingType(val clazz: KClass<out Any>) {
CHAR(Char::class),
STRING(String::class),
INT(Int::class),
}
So I added a clazz so from the enum we know the Kotlin type
and now a function to simulate your repository fetch
fun findAppSettingByName(name: String): AppSetting? {
return when(name) {
"Char thing" -> AppSetting(value= "C", type = AppSettingType.CHAR)
"String thing" -> AppSetting(value= "Str", type = AppSettingType.STRING)
"Int thing" -> AppSetting(value= "42", type = AppSettingType.INT)
else -> throw IllegalArgumentException()
}
}
Next in the function declaration I have made it generic with T and for the purposes of the demo removed the DatabaseResult container. Then I added a clazz parameter which is the typical Java way of carrying the required class information into the function:
fun <T : Any> getAppSetting(name: String, clazz: KClass<T>): T? {
val appSetting: AppSetting? = findAppSettingByName(name)
return appSetting?.let {
require(clazz == appSetting.type.clazz) {
"appSetting.type=${appSetting.type.clazz} mismatched with requested class=${clazz}"
}
when (appSetting.type) {
AppSettingType.CHAR -> appSetting.value.first()
AppSettingType.STRING -> appSetting.value
AppSettingType.INT -> appSetting.value.toInt()
} as T
}
}
the as T is important to cast the values into the required return type - this is unchecked but the when() clause should be creating the correct types.
Now let's test it:
val c1: Char? = getAppSetting("Char thing", Char::class)
val s1: String? = getAppSetting("String thing", String::class)
val i1: Int? = getAppSetting("Int thing", Int::class)
println("c1=$c1 s1=$s1 i1=$i1")
val c2: Char? = getAppSetting("Char thing")
val s2: String? = getAppSetting("String thing")
val i2: Int? = getAppSetting("Int thing")
println("c2=$c2 s2=$s2 i2=$i2")
}
The output is
c1=C s1=Str i1=42
c2=C s2=Str i2=42
But how do c2/s2/i2 work, the final part is this function
inline fun <reified T : Any> getAppSetting(name: String) = getAppSetting(name, T::class)
This is reified generic parameters... there is no need to pass the clazz because this can be found from the data type of the receiving variable.
There are many articles about this advanced topic, e.g.
https://typealias.com/guides/getting-real-with-reified-type-parameters/
https://medium.com/kotlin-thursdays/introduction-to-kotlin-generics-reified-generic-parameters-7643f53ba513
Now, I didn't completely answer what you wanted because you wanted to receive a DatabaseResult<T> wrapper. What might be possible, is to have a function that returns DatabaseResult<T> and you can obtain the T from it as the "clazz" parameter, but I'll leave that for someone else to improve on :-) but I think that gets you pretty close.
package com.example.learning
fun main(args: Array<String>) {
var person = Person("Ramu", 51, 50000F, 7.5F)
person.apply{
name = "Sam"
id = 1
details()
}.details()
}
Q1)What is the difference in calling details or any class method inside and outside the apply block?
Q2)Here in the apply block can I call multiple class methods at once like calling Salary and Details at the same time outside the apply block with .details()&.salary()?
class Person(var name: String, var id: Int, var sal: Float, var salRaise: Float){
fun details(){
println("The name of the person is $name with id $id and salary if $sal")
}
fun salary(): Float{
sal *= salRaise
return sal
}
}
apply is just a convenience method so you don't have to write person every time.
This:
person.apply{
name = "Sam"
id = 1
details()
}
is the same as doing:
person.name = "Sam"
person.id = 1
person.details()
I'm not sure what you mean by your second question. You ask how to call those 2 methods outside a apply? Just do
person.details()
person.salary()
There's another benefit to using apply. If person could be null you could do person?.apply to only change those fields in the case the person is not null. So this for example:
fun changePerson(person : Person?) {
person?.apply{
name = "Sam"
id = 1
details()
}
}
is the same as
fun changePerson(person : Person?) {
if (person != null) {
person.name = "Sam"
person.id = 1
person.details()
}
}
EDIT:
If you want to be able to chain the salary() after a details() you could do it by making this change:
class Person(var name: String, var id: Int, var sal: Float, var salRaise: Float){
fun details() : Person{
println("The name of the person is $name with id $id and salary if $sal")
return this
}
fun salary(): Float{
sal *= salRaise
return sal
}
}
then you could do this for example:
person.apply{
name = "Sam"
id = 1
}.details().salary()
We are using kotlin dsl to as a user friendly builder to take input and generate data. Is there a way to do the opposite of that ?
ie, convert existing data into dsl ?
Can this kotlin representation be converted to dsl ?
val person = Person("John", 25)
val person = person {
name = "John"
age = 25
}
Unless you're really crazy about { and some commas, below is an absolutely valid Kotlin code:
data class Person(
val name: String,
val age: Int
)
val person = Person(
name = "John",
age = 25
)
I seems really close to what you want and comes out-of-the-box.
Of course, you can achieve the syntax you want by writing some extra code, like:
import kotlin.properties.Delegates
data class Person(
val name: String,
val age: Int
)
class PersonDSL{
lateinit var name: String
var age: Int by Delegates.notNull<Int>()
fun toPerson(): Person = Person(this.name, this.age)
}
fun person(config: PersonDSL.() -> Unit): Person{
val dsl = PersonDSL()
dsl.config()
return dsl.toPerson()
}
fun main(){
val person = person {
name = "John"
age = 25
}
println(person) // Person(name=John, age=25)
}
But why do that?
First of all my code:
Table 1:
object Company : Table() {
val name = varchar("pk_name", 250)
override val primaryKey = PrimaryKey(name, name = "pk_company_constraint")
}
Table 2&3:
object Sector : IntIdTable() {
val name = varchar("fk_name", 50).references(MainSector.name)
val alias = varchar("alias", 50).nullable()
val companyName = varchar("fk_company_name", 250).references(Company.name, onDelete = ReferenceOption.CASCADE)
}
object MainSector : Table() {
val name = varchar("pk_name", 50)
override val primaryKey = PrimaryKey(name, name = "pk_main_sector_constraint")
}
My Problem:
I need to parse the result into a DTO that looks like this:
data class CompanyDTO (
val companyName: String,
val sectorList: List<SectorDTO>
)
data class SectorDTO (
val mainSectorName: String,
val sectorAlias: String
)
I am able to get a Company with the first Sector from the database, but i have no idea how to get a list of them.
My try:
override fun retrieveCompanies(vararg names: String): List<CompanyDTO> {
var retlist: List<CompanyDTO> = emptyList()
if (names.isEmpty()){
retlist = transaction {
(Company innerJoin Sector)
.select{Company.name eq Sector.companyName}
.map { CompanyDTO(it[Company.name], listOf(
SectorDTO(it[Sector.name], it[Sector.alias]?: "")
)) }
}
} else {
//return specific
}
return retlist
}
If no arguments are given i want to return all companies from the database, if arguments are given i want to return only companies with given name.
I can´t find anything about this topic in the official documentation, please send help
If Company could not have any Sector you need to use leftJoin and then your code could be like:
Company.leftJoin.Sector.selectAll().map {
val companyName = it[Company.name]
val sector = it.tryGet(Sector.name)?.let { name ->
SectorDTO(name, it[Sector.alias].orEmpty())
}
companyName to sector
}.groupBy({ it.first }, { it.second }).map { (companyName, sectors) ->
CompanyDTO(companyName, sectors.filterNotNull())
}
i would liek to run the simple example mentioned below. eclipse generates an error says:
main class cant be found or loaded
please let me know how to fix this error and why it happens
in the below code I am trying to use the backing fields. however, the way they are used in the code does not provide the expected output.
please refer to the output section.
how to display output of the backing fields
code:
fun main(args: Array<String>) {
println("Hello, World!")
val p1 = Person_1("jack", 21);
p1.lastName = "stephan"
p1.month = "may"
println("lastName is ${p1.getLastName}")
println("month is ${p1.getMonth}")
val p2 = Person_1("jack", 21);
p2.lastName = "knauth"
p2.month = "june"
println(p2.getLastName)
println(p2.getMonth)
class Person_1 (val name: String, val age : Int) {
//backing field 1
var lastName : String? = null
set(value) {
if (value?.length == 0) throw IllegalArgumentException("negative values are not allowed")
field = value
}
val getLastName
get() = {
lastName
}
//backing field 2
var month : String? = null
set(value) {
field = value
}
val getMonth
get() = {
month
}
}
output:
Hello, World!
lastName is () -> kotlin.String?
month is () -> kotlin.String?
() -> kotlin.String?
() -> kotlin.String?
You can just get rid of your getters like this:
class Person_1 (val name: String, val age : Int) {
//backing field 1
var lastName : String? = null
set(value) {
if (value?.length == 0) throw IllegalArgumentException("negative values are not allowed")
field = value
}
//backing field 2
var month : String? = null
set(value) {
field = value
}
}
If later you'll need them you can add it like this without api changes:
var lastName : String? = null
get() = field
set(value) {
if (value?.length == 0) throw IllegalArgumentException("negative values are not allowed")
field = value
}