How to use Loop in PromiseKit 6?

Question

I have a function called chaining which chains multiple promises and I want to call that function multiple times. For that, I am using a for loop and I want that with index 0, the chaining function should be executed with index 0. (I have an array of properties ListingArray[] and I want to use ListingArray[0] in one iteration of loop, ListingArray[1] in other iteration and so on).

Here is my chaining function:

func chaining() {
  
 firstly {
            Promise_getIDOfOwnerFromCollection()
        
 }.then { (IdsInCollection)-> Promise<[String]> in
        
        return self.Promise_getOwnerListings(IDs: IdsInCollection)
            
 }.then { (ownerListings) ->Promise<Void> in

            return self.Promise_getReviews(ListingIDs: ownerListings)
           
 }.done { (arg0) in
            
            
            let () = arg0
            print("Work Done")
            
 }.catch { (error) in
            print("Error is \(error.localizedDescription)")
    }
 }

And I am calling that function in loop like this.

for Count in 0...4 {
  chaining()
 }

Now the problem is that the function inside firstly is instantly called 5 times before then is executed. And I want the sequence to be like with Count 0, chaining function should execute one time and then with Count 1, function should execute again.

Answer 1

The behaviour happening in your code is completely expected. Given you're instantiating the chaining 4 times, therefore the firstly job will be executed such number of times.

Instead you will need somehow provide a single instance of work for the firstly.

Currently: execute N times { firstly + rest of the job }

Expected: firstly + execute N times { rest of the job }

Here a code example based on yours.

struct Review {

}

func Promise_getReviews(listingIDs ids: [String]) -> Promise<[Review]> {

}

func Promise_getOwnerListings(IDs ids: [String]) -> Promise<[String]> {

}

func chaining(from initialWork: Promise<[String]>) {
    firstly { when(fulfilled: initialWork) }
        .then(Promise_getOwnerListings)
        .then(Promise_getReviews)
        .done { print("Work Done") }
        .catch { print("Error") }
}

let initialWork = Promise<[String]>(["1","2", "3"])

(0...3).forEach { chaining(from: initialWork) }