How to create basic pagination logic in Gatling? - scala

Question

So I am trying to create basic pagination in Gatling but failing miserably.
My current scenario is as follows:
1) First call is always a POST request, the body includes page index 1 and page size 50
{"pageIndex":1,"pageSize":50}
I am then receiving 50 object + the total count of objects on the environment:
"totalCount":232
Since I need to iterate through all objects on the environment, I will need to POST this call 5 time, each time with an updated pageIndex.
My current (failing) code looks like:
def getAndPaginate(jsonBody: String) = {
val pageSize = 50;
var totalCount: Int = 0
var currentPage: Int = 1
var totalPages: Int =0
exec(session => session.set("pageIndex", currentPage))
exec(http("Get page")
.post("/api")
.body(ElFileBody("json/" + jsonBody)).asJson
.check(jsonPath("$.result.objects[?(#.type == 'type')].id").findAll.saveAs("list")))
.check(jsonPath("$.result.totalCount").saveAs("totalCount"))
.exec(session => {
totalCount = session("totalCount").as[Int]
totalPages = Math.ceil(totalCount/pageSize).toInt
session})
.asLongAs(currentPage <= totalPages)
{
exec(http("Get assets action list")
.post("/api")
.body(ElFileBody("json/" + jsonBody)).asJson
.check(jsonPath("$.result.objects[?(#.type == 'type')].id").findAll.saveAs("list")))
currentPage = currentPage+1
exec(session => session.set("pageIndex", currentPage))
pause(Config.minDelayValue seconds, Config.maxDelayValue seconds)
}
}
Currently the pagination values are not assign to the variables that I have created at the beginning of the function, if I create the variables at the Object level then they are assigned but in a manner which I dont understand. For example the result of Math.ceil(totalCount/pageSize).toInt is 4 while it should be 5. (It is 5 if I execute it in the immediate window.... I dont get it ). I would than expect asLongAs(currentPage <= totalPages) to repeat 5 times but it only repeats twice.
I tried to create the function in a class rather than an Object because as far as I understand there is only one Object. (To prevent multiple users accessing the same variable I also ran only one user with the same result)
I am obviously missing something basic here (new to Gatling and Scala) so any help would be highly appreciated :)

Answer 1

using regular scala variables to hold the values isn't going to work - the gatling DSL defines builders that are only executed once at startup, so lines like
.asLongAs(currentPage <= totalPages)
will only ever execute with the initial values.
So you just need to handle everything using session variables
def getAndPaginate(jsonBody: String) = {
val pageSize = 50;
exec(session => session.set("notDone", true))
.asLongAs("${notDone}", "index") {
exec(http("Get assets action list")
.post("/api")
.body(ElFileBody("json/" + jsonBody)).asJson
.check(
jsonPath("$.result.totalCount")
//transform lets us take the result of a check (and an optional session) and modify it before storing - so we can use it to get store a boolean that reflects whether we're on the last page
.transform( (totalCount, session) => ((session("index").as[Int] + 1) * pageSize) < totalCount.toInt)
.saveAs("notDone")
)
)
.pause(Config.minDelayValue seconds, Config.maxDelayValue seconds)
}
}