I'll appreciate all your help.
I've been working on a course project where I have to make a parking lot that registers cars. When I use it in my IDE it works fine but when I run it through the platforms tests, in the first one, there's no problem but when the second iteration reaches the "when (val command = scanner.next())" in the createOrder fun, it crashes with the error:
java.lang.AssertionError: Exception in test #1
Probably your program run out of input (Scanner tried to read more than expected).
java.util.NoSuchElementException
at java.util.Scanner.throwFor(Scanner.java:862)
at java.util.Scanner.next(Scanner.java:1371)
at parking.ParkingLot.createOrder(Main.kt:39)
at parking.ParkingLot.start(Main.kt:31)
at parking.MainKt.main(Main.kt:6)
at parking.MainKt.main(Main.kt)
Please find below the output of your program during this failed test.
Note that the '>' character indicates the beginning of the input line.
---
> park KA-01-HH-1234 White
White car parked in spot 1.
the idea is that the test inputs many cars but it crashes when trying to do the second input
this is my code (sorry if my code is messy, I'm still learning)
import java.util.*
fun main() {
ParkingLot.start()
}
class Car(val regNumber: String = "", val color: String = "") {
}
class Order(val command: String) {
lateinit var regNum: String
lateinit var color: String
lateinit var spot: String
lateinit var status: String
}
object ParkingLot {
val spaces: Array<Pair<String?, Car?>> = Array(20) { Pair(null, null) }
const val occupied = "occupied"
const val park = "park"
const val leave = "leave"
const val exit = "exit"
fun start() {
val scanner = Scanner(System.`in`)
do {
val order = createOrder(scanner)
interaction(order, scanner)
} while (order.command != exit)
}
fun createOrder(scanner: Scanner): Order {
when (val command = scanner.next()) {
park -> {
val parkOrder = Order(command)
parkOrder.regNum = scanner.next()
parkOrder.color = scanner.next()
parkOrder.status = "valid"
return parkOrder
}
leave -> {
val retrieveOrder = Order(command)
retrieveOrder.spot = scanner.next()
retrieveOrder.status = "valid"
return retrieveOrder
}
exit -> {
val exitOrder = Order(command)
exitOrder.status = "valid"
return exitOrder
}
else -> {
val incorrectOrder = Order(command)
incorrectOrder.status = "invalid"
return incorrectOrder
}
}
}
fun interaction(order: Order, scanner: Scanner) {
if (order.command == park) {
// val toParkCar = Car(order.regNum, order.color)
park(Car(order.regNum, order.color))
}
if (order.command == leave) {
leave(order)
}
if (order.command == exit) return
//TODO update the error msg to include exit command
if (order.status == "invalid") println("\"${order.command}\" isn't a valid , either use \"park\" or \"leave\"")
// scanner.close()
}
fun park(car: Car) {
for ((index, item) in spaces.withIndex()) {
if (item.first == null) {
spaces[index] = Pair(occupied, car)
println("${car.color} car parked in spot ${index + 1}.")
return
}
}
println("Sorry, the parking lot is full.")
}
fun leave(order: Order) {
if (spaces[order.spot.toInt() - 1].first == occupied) {
spaces[order.spot.toInt() - 1] = Pair(null, null)
println("Spot ${order.spot} is free.")
} else {
println("There is no car in spot ${order.spot}.")
}
}
}
Ok so I noticed this is a problem for the JetBrains plugin. I don't know why but the solution was taking the scanner out of the function and directly in the main loop.
I have never worked before with Kotlin so I have a newbie question. I am working with an existing codebase, so I am wondering about a few things. I see that there is a function getDepartmentById which looks like this:
fun getDepartmentById(ctx: Ctx, params: JsonObject): Either<Failure, FlatResp> =
getOneByIdFlattened(ctx, params.right(), getDepartmentByIdSql(ctx), flattenOne = flattenerToType(MainAccessType.DEPARTMENT))
fun getDepartmentById(ctx: Ctx, id: Long): Either<Failure, FlatResp> =
getDepartmentById(ctx, jsonObject("id" to id))
Calling that function returns either Failure or FlatResp. From what I can see in the code FlatResponse is typealias for Map<MainAccessType, Entities>.
The function getOneByIdFlattened looks like this:
fun getOneByIdFlattened(ctx: Ctx,
params: Either<Long, JsonObject>,
statement: String,
rowConverter: (Row) -> Map<String, Any?> = ::mapFromDbNames,
grouper: (List<Map<String, Any?>>) -> List<Map<String, Any?>> = ::identity,
flattenOne: (List<Map<String, Any?>>) -> FlatResp
): Either<Failure, FlatResp> =
either.eager {
val id = when (params) {
is Either.Left -> Either.Right(params.value)
is Either.Right -> params.value.idL?.right()
?: Failure.JsonError(SErr(GlowErrs.MISSING_ID, "You must provide id")).left()
}.bind()
val dbDataList: List<Map<String, Any?>> = doQuery(ctx, statement, mapOf(
"courierIds" to ctx.user.courierIds,
"id" to id,
"count" to 1,
"offset" to 0,
"departmentIds" to ctx.userDepartments,
"customerIds" to ctx.user.customerIds
),
rowConverter, false
).bind()
val result = flattenOne(grouper(dbDataList))
addUpdatedAtEpoch(result)
}
I wonder how can I get from a FlatResp a property of an object, that looks like this:
So, for example if I want to get just name from this object what would be the best way to do this?
Also, I wonder why is this function returning a collection, and not just a single object when it should get a single row by id from DB?
This is the sql function:
private fun getDepartmentByIdSql(ctx: Ctx) =
"""select ${createSelectFields(departmentKeys)}
from department dept
where dept.id = :id
${
when (ctx.user.role) {
UserRoles.ADMIN -> ""
else -> "and dept.id = any (:departmentIds) "
}
}"""
So there are a lot of things wrong in the snippet provided. Given Snippets:
1
fun getDepartmentById(ctx: Ctx, params: JsonObject): Either<Failure, FlatResp> =
getOneByIdFlattened(ctx, params.right(), getDepartmentByIdSql(ctx), flattenOne = flattenerToType(MainAccessType.DEPARTMENT))
2
fun getDepartmentById(ctx: Ctx, id: Long): Either<Failure, FlatResp> =
getDepartmentById(ctx, jsonObject("id" to id))
3
private fun getDepartmentByIdSql(ctx: Ctx) =
"""select ${createSelectFields(departmentKeys)}
from department dept
where dept.id = :id
${
when (ctx.user.role) {
UserRoles.ADMIN -> ""
else -> "and dept.id = any (:departmentIds) "
}
}"""
4
fun getOneByIdFlattened(ctx: Ctx,
params: Either<Long, JsonObject>,
statement: String,
rowConverter: (Row) -> Map<String, Any?> = ::mapFromDbNames,
grouper: (List<Map<String, Any?>>) -> List<Map<String, Any?>> = ::identity,
flattenOne: (List<Map<String, Any?>>) -> FlatResp
): Either<Failure, FlatResp> =
either.eager {
val id = when (params) {
is Either.Left -> Either.Right(params.value)
is Either.Right -> params.value.idL?.right()
?: Failure.JsonError(SErr(GlowErrs.MISSING_ID, "You must provide id")).left()
}.bind()
val dbDataList: List<Map<String, Any?>> = doQuery(ctx, statement, mapOf(
"courierIds" to ctx.user.courierIds,
"id" to id,
"count" to 1,
"offset" to 0,
"departmentIds" to ctx.userDepartments,
"customerIds" to ctx.user.customerIds
),
rowConverter, false
).bind()
val result = flattenOne(grouper(dbDataList))
addUpdatedAtEpoch(result)
}
Issues:
in snippet 2, jsonObject should be JsonObject(..)
I have no idea what the following lines do :
//snippet1:
flattenOne = flattenerToType(MainAccessType.DEPARTMENT))
//snipper 4
either.eager {...block...}
addUpdatedAtEpoch(result)
doQuery(ctx, statement, mapOf(..)
//snippet3
UserRoles.ADMIN -> ""
"""select ${createSelectFields(departmentKeys)}
They are all probably some extension functions or util files made by your company or from some famous libraries like anko orsplitties . plus these are mixes with function calls of your own class, like createSelectFields or ctx.user.courierIds. also if i have to guess, then this seems like an unusual way of performing some operation on an sql dB
based on just code completion by android studio, i have been able to figure out the classes as following:
class Entities
typealias FlatResp = Map<MainAccessType, Entities>
class Ctx
sealed class Either<A,B>(val a:A?, val b:B?){
val value:A? = null
class Left<A>(val aa:A):Either<A,A>(aa,aa)
class Right<B>(val bv:B):Either<B,B>(bb,bb)
}
class Failure
class Row
class JsonObject(val pair:Pair<String,Long>):JSONObject(){
fun right():Either<Long,JsonObject>{
}
}
class jsonObject()
enum class MainAccessType{DEPARTMENT}
fun getDepartmentById(ctx: Ctx, params: JsonObject): Either<Failure, FlatResp> {
return getOneByIdFlattened(
ctx,
params.right(),
getDepartmentByIdSql(ctx),
flattenOne = flattenerToType(MainAccessType.DEPARTMENT))
}
fun getDepartmentById(ctx: Ctx, id: Long): Either<Failure, FlatResp> {
return getDepartmentById(ctx, JsonObject("id" to id))
}
fun getOneByIdFlattened(ctx: Ctx,
params: Either<Long, JsonObject>,
statement: String,
rowConverter: (Row) -> Map<String, Any?> = ::mapFromDbNames,
grouper: (List<Map<String, Any?>>) -> List<Map<String, Any?>> = ::identity,
flattenOne: (List<Map<String, Any?>>) -> FlatResp
): Either<Failure, FlatResp> {
return either.eager {
val id = when (params) {
is Either.Left -> Either.Right(params.value)
is Either.Right -> params.value.idL?.right()
?: Failure.JsonError(SErr(GlowErrs.MISSING_ID, "You must provide id")).left()
}.bind()
val dbDataList: List<Map<String, Any?>> = doQuery(ctx, statement, mapOf(
"courierIds" to ctx.user.courierIds,
"id" to id,
"count" to 1,
"offset" to 0,
"departmentIds" to ctx.userDepartments,
"customerIds" to ctx.user.customerIds
),
rowConverter, false
).bind()
val result = flattenOne(grouper(dbDataList))
addUpdatedAtEpoch(result)
}
}
private fun getDepartmentByIdSql(ctx: Ctx) =
"""select ${createSelectFields(departmentKeys)}
from department dept
where dept.id = :id
${
when (ctx.user.role) {
UserRoles.ADMIN -> ""
else -> "and dept.id = any (:departmentIds) "
}
}"""
fun mapFromDbNames(row:Row): Map<String,Any?>{
}
fun identity(param : List<Map<String, Any?>>): List<Map<String, Any?>>{
}
This is still not correct and has a lots of red lines in it. but what you can do is keep this as a starter in a separate file, compare and fix the code accordingly and then maybe we can tell what would be a better way:
replace inline functions (fun xyz(...) = someValue ) to block functions. (alt+enter in windows, cmd+n in mac)
instead of typeAlias, use map directly
::something means a function is passed as parameter . its similar to how we pass runnables in java 8, but even more shorthand. you can do ctrl+click( for mac its cmd+click) on that function and goto that function to check what its params are, what its return type are. do the same for various classes/ extension fucntions, variables too. this will help the most
instead of passing something into something which is being passed into another thing (like val bot = Robot(Petrol("5Litres") ) ) , split into different lines to make it understandable ( val amount = "5litres"; val equipment = Petrol(amount) ; val bot = Robot(equipment) )
try to not use 3rd party library/ replace with your own understandable code.
repeat steps 1-5
Hope this gives someplace to start. kotlin is a beautiful language but is also very easy to make unreadable.
Mapping Map values
I wonder how can I get from a FlatResp a property of an object, that looks like this:
So, for example if I want to get just name from this object what would be the best way to do this?
TL;DR
Without data to work with, here's my guess:
val extractedNames: Map<Long, String?> = destinationDepartment
.mapValues { (_, userData: Map<String, Any?>) ->
when (val name = userData["name"]) {
is String -> name
else -> null
}
}
println(extractedNames)
// {1=Bergen, 2=Cindy, 3=Dave}
Intro
Kotlin is great for manipulating collections. For a more general of how to work with collections in Kotlin, I think the docs are really clear Collection transformation operations#Map.
Let's see how that works for this example. You want to extract a specific element, so for that we can use map().
From your screenshot it looks like this is a Map<Long, Map>, where the value is a Map<String, Any?>. I'll assume you want to change the Map<Long, Map> to a Map<Long, String>, where the key is the database ID and the value is user's name.
Test data
So I've got something to test with, I made a new Map:
val destinationDepartment: Map<Long, Map<String, Any?>> =
mapOf(
1L to mapOf(
"id" to 1,
"name" to "Bergen",
"createdAt" to LocalDateTime.now(),
"updatedAt" to LocalDateTime.now(),
),
2L to mapOf(
"id" to 2,
"name" to "Cindy",
"createdAt" to LocalDateTime.now(),
"updatedAt" to LocalDateTime.now(),
),
3L to mapOf(
"id" to 3,
"name" to "Dave",
"createdAt" to LocalDateTime.now(),
"updatedAt" to LocalDateTime.now(),
),
)
Basic noop
First, set up the basics. A Map can be converted to a list of Entries. When we call map(), it will iterates over each Entry, and applies a lambda - which is something we must write. In this instance, the lambda receives the key and value of the Map, and must return a new value.
Aside: the Java equivalent is map.entrySet().stream().map(...)...
Here, the lambda just returns a pair (created with to).
val extractedNames = destinationDepartment
.map { (id: Long, userData: Map<String, Any?>) ->
id to userData
}
println(extractedNames)
// Output: [(1, {id=1, name=Bergen, createdAt=2021-08-19T11:00:07.447660, updatedAt=2021-08-19T11:00:07.449969}),
// (2, {id=2, name=Cindy, createdAt=2021-08-19T11:00:07.463813, updatedAt=2021-08-19T11:00:07.463845}),
// (3, {id=3, name=Dave, createdAt=2021-08-19T11:00:07.463875, updatedAt=2021-08-19T11:00:07.463890})]
Pretty boring! But now we're set up for the next step - extracting name from userData: Map<String, Any?>.
Extracting name
val extractedNames = destinationDepartment
.map { (id: Long, userData: Map<String, Any?>) ->
val name = userData["name"]
id to name
}
println(extractedNames)
// Output: [(1, Bergen), (2, Cindy), (3, Dave)]
Now there's loads of ways to improve this. Making sure that name is a String, not Any?, filtering out blank or null names, mapping to DTOs, sorting. Again, the Kotlin documentation would be a good start. I'll start by listing one really good improvement.
Converting List<Pair<>> to Map<>
If you look at the type of val extractedNames, you'll see that it's a list, not a map.
val extractedNames: List<Pair<Long, Any?>> = ...
That's because the lambda we wrote in the map() function is returning a Pair<Long, String>. Kotlin doesn't know that this is still considered a Map. We can convert any List<Pair<>> back to a map with toMap()
toMap()
val extractedNames: Map<Long, Any?> = destinationDepartment
.map { (id: Long, userData: Map<String, Any?>) ->
val name = userData["name"]
id to name
}
.toMap() // convert List<Pair<>> to a Map<>
println(extractedNames)
// Output: {1=Bergen, 2=Cindy, 3=Dave}
But this is also not great. Why is id: Long in the lambda if we're not using it? Because we're only extracting the name from userData, we're only mapping the values of the Map. We don't need id: Long at all. Fortunately Kotlin has another useful method: mapValues() - and it returns a Map<>, so we can drop the toMap(). Let's use it.
mapValues()
val extractedNames: Map<Long, Any?> = destinationDepartment
.mapValues { (id: Long, userData: Map<String, Any?>) ->
val name = userData["name"]
id to name
}
println(extractedNames)
// {1=(1, Bergen), 2=(2, Cindy), 3=(3, Dave)}
Umm weird. Why are the ids in the values? That's because the mapValues() lambda should return the new value, and in our lambda we're returning both the id and name - oops! Let's only return the name.
Fixing mapValues()
val extractedNames: Map<Long, Any?> = destinationDepartment
.mapValues { (_, userData: Map<String, Any?>) ->
userData["name"]
}
println(extractedNames)
// {1=(1, Bergen), 2=(2, Cindy), 3=(3, Dave)}
Better! Because id is not used, an underscore can be used instead
Aside: Note that the lambda doesn't have a return. Read Returning a value from a lambda expression for an explanation.
First of all, I've only started learning corda 3 months ago so I've got some learning to do.
I've inherited some code that runs fine under Corda v3.3 but the customers want it to run on v4. I'm trying to follow the instructions on the main website. I've got an initiating flow which calls a subflow, which in turn calls a transponder flow.
The initiating flow:
#InitiatingFlow(version = 2)
#StartableByRPC
class TransferFlow(private val issuerName: String = "",
private val seller: String = "",
private val amount: BigDecimal = BigDecimal("0"),
private val buyer: String = "",
private val custodianNameOfBuyer: String = "",
private val notaryName: String = "") : FlowLogic<SignedTransaction>() {
#Suspendable
override fun call(): SignedTransaction {
subFlow(UpdateStatusOfTransferFlow(
sessions,
tokenTransferAgreement.linearId,
"Removed Tokens From Seller"))
}
}
class UpdateStatusOfTransferFlow(
private val sessions: Set<FlowSession>,
private val tokenTransferAgreementID: UniqueIdentifier,
private val newStatus: String) : FlowLogic<SignedTransaction>() {
#Suspendable
override fun call(): SignedTransaction {
sessions.size
val idQueryCriteria = QueryCriteria.LinearStateQueryCriteria(linearId = listOf(tokenTransferAgreementID))
val states = serviceHub.vaultService.queryBy<TokenTransferAgreement>(idQueryCriteria).states
if (states.size != 1) throw FlowException("Can not find a unique state for $tokenTransferAgreementID")
val inputStateAndRef = states.single()
val inputState = inputStateAndRef.state.data
val notary = inputStateAndRef.state.notary
val outputState = inputState.withNewStatus(newStatus)
val cmd = Command(TokenContract.Commands.UpdateStatusOfTransfer(),
inputState.participants.map { it.owningKey })
val txBuilder = TransactionBuilder(notary = notary)
txBuilder.addCommand(cmd)
txBuilder.addInputState(inputStateAndRef)
txBuilder.addOutputState(outputState, TokenContract.ID)
txBuilder.verify(serviceHub)
val ptx = serviceHub.signInitialTransaction(txBuilder)
val sessions2 = (inputState.participants.toSet() - ourIdentity).map { initiateFlow(it) }
return subFlow(CollectSignaturesFlow(ptx, sessions2))
}
}
And the responder:
#InitiatedBy(TransferFlowResponder::class)
class UpdateStatusOfTransferFlowResponder(private val session: FlowSession) : FlowLogic<Unit>() {
#Suspendable
override fun call() {
val tokenTransferAgreements = mutableListOf<TokenTransferAgreement>()
var isBuyer = true
var notary = CordaUtility.getNotary(serviceHub) ?: throw FlowException("An notary is expected!")
val signedTransactionFlow = subFlow(object : SignTransactionFlow(session) {
override fun checkTransaction(stx: SignedTransaction) = requireThat {
"There must be one output!" using (stx.tx.outputStates.size == 1)
val tokenTransferAgreement = stx.tx.outputStates.first() as TokenTransferAgreement
tokenTransferAgreements.add(tokenTransferAgreement)
notary = stx.notary ?: throw FlowException("An notary is expected!")
if (ourIdentity == tokenTransferAgreement.issuer) {
//checks go here
}
})
}
}
I believe I am supposed to add a call to ReceiveFinality flow at some point, however it only takes 1 session as an argument, not a list as I have here. Should I make multiple calls, one for each session? I am also not sure if the calls should go in the transponder or the UpdateStatusOfTransferFlow class.
Help here would be appreciated.
The FinalityFlow is mainly responsible for ensuring transactions are notarized, distributed accordingly and persisted to local vaults.
In previous versions of Corda, all nodes would by default accept incoming requests for finality.
From V4 onwards, you're required to write a ReceiveFinalityFlow to write your own processing logic before finality.
The way finality currently runs in Corda is the initiating node, as an intermediate step during finality, distributes notarised transaction to all other participants. Each of the participating nodes it sends to will only expect to receive a session from this node.
So where you might submit multiple sessions to the initiating FinalityFlow to include all the participants, the responding nodes will only ever receive just the one session from the initiator.
In the future, we may look at having the Notary distribute the notarized transaction to all participants, but even then, the ReceiveFinalityFlow would still only expect one session, this time from the Notary.
This might be a bit too specific for posting here, but I'm trying to generate a class like this with kotlinpoet:
class Query<out E: Model>(val onSuccess: (E) -> Unit, val onError: (Int, String) -> Unit = { i, m -> })
How would I create that type/constructor parameter with kotlinpoet? The docs do have the "Unit" type listed along with primitive types, so it seems to be a special case.
Here's a program producing the output you need:
class Model
fun main(args: Array<String>) {
val onSuccessType = LambdaTypeName.get(
parameters = TypeVariableName(name = "E"),
returnType = Unit::class.asTypeName())
val onErrorType = LambdaTypeName.get(
parameters = listOf(Int::class.asTypeName(), String::class.asTypeName()),
returnType = Unit::class.asTypeName())
val primaryConstructor = FunSpec.constructorBuilder()
.addParameter(ParameterSpec.builder(name = "onSuccess", type = onSuccessType)
.build())
.addParameter(ParameterSpec.builder(name = "onError", type = onErrorType)
.defaultValue("{ i, m -> }")
.build())
.build()
val querySpec = TypeSpec.classBuilder("Query")
.addTypeVariable(TypeVariableName(name = "out E", bounds = Model::class))
.addProperty(PropertySpec.builder(name = "onSuccess", type = onSuccessType)
.initializer("onSuccess")
.build())
.addProperty(PropertySpec.builder(name = "onError", type = onErrorType)
.initializer("onError")
.build())
.primaryConstructor(primaryConstructor)
.build()
val file = KotlinFile.builder(packageName = "", fileName = "test")
.addType(querySpec)
.build()
file.writeTo(System.out)
}
This prints (excluding generated imports) the following:
class Query<out E : Model>(val onSuccess: (E) -> Unit,
val onError: (Int, String) -> Unit = { i, m -> })
I'm hacking TypeVariableName here as out E, since there seems to be no better solution at the time. I'm also using the 0.4.0-SNAPSHOT version.
Easily enough, it's done by using the LambdaTypeName class. It was a bit confusing after getting used to kotlin's functional type style as opposed to java strictly functional interfaces. Here's what I used:
val typeVariable = TypeVariableName.invoke("E")
.withBounds(QueryData::class)
ParameterSpec.builder("onSuccess",
LambdaTypeName.get(null, listOf(typeVariable), UNIT)).build()
Which generates (with the class builders, of course):
class Query<E : QueryData> {
constructor(onSuccess: (E) -> Unit) {
}
}