How to call recursive function with Promise Kit? - swift

Question

I am stuck with somewhere to call same function again in promise and because of calling multiple time it's deallocate promise. Actually in my case I have API with multiple page request and I want to call it with promise. I was implemented it as below.
func fetchContacts() -> Promise<FPGetContactResponse?> {
return Promise { seal in
let contactrequest = FPGetContactRequest()
contactrequest.pageNo = getAPICurrentPageNo(Api.API_CONTACTS) + 1
contactrequest.pageSize = SMALL_PAGE_SIZE
contactrequest.doGetContacts(parameter: [:], response: { (response) in
print("Contacts Count : \(response.Contacts?.count ?? 0)")
if(response.Contacts?.count ?? 0 != 0){
_ = self.fetchContacts()
}else{
seal.fulfill(response)
}
})
{ (error) in
print(error.localizedDescription)
seal.reject(error)
}
}
}
In above function I check for contact count != 0 then I need to call same function again. But unfortunately it's deallocate promise.
I call promise sequence like below.
func startSyncData(handler:#escaping SyncAPIHandler){
firstly {
self.fetchContacts().ensure {
handler(false,0.5,nil)
}
}.then { data in
self.fetchInteractions().ensure {
handler(false,0.7,nil)
}
}.then { data in
self.fetchAddresses().ensure {
handler(false,0.8,nil)
}
}.then { data in
self.fetchLookupQuery().ensure {
}
}
.done { contacts -> Void in
//Do something with the JSON info
print("Contacts Done")
handler(true,0.8,nil)
}
.catch(policy: .allErrors) { error in
print(error.localizedDescription)
}
}
Please provide me the right way to call same function again in promise.

Answer 1

Instead of using recursion you should return a response within your promise and check it inside next .then and call fetchContacts again if it's needed:
fetchContacts()
.then { response -> Promise<FPGetContactResponse> in
if (response.Contacts?.count ?? 0 != 0) {
return fetchContacts() // Make the second call
}
return .value(response) // Return fullfilled promise
}
.then {
...
}
Also you can make a special wrapper for your case using the next approach - https://github.com/mxcl/PromiseKit/blob/master/Documentation/CommonPatterns.md#retry--polling

Answer 2

I implemented things with following solution.
func syncContacts() -> Promise<FPGetContactResponse?> {
return fetchContacts().then{ seal -> Promise<FPGetContactResponse?> in
if(seal?.Contacts?.count ?? 0 != 0){
return self.syncContacts()
}else{
return Promise.value(seal)
}
}
}
Now just call syncContacts() method in promise sequence, like below.
func startSyncData(handler:#escaping SyncAPIHandler){
firstly {
self.syncContacts().ensure {
handler(false,0.5,nil)
}
}.then { data in
self.syncInterections().ensure {
handler(false,0.7,nil)
}
}.then { data in
self.syncAddresses().ensure {
handler(false,0.8,nil)
}
}.then { data in
self.syncLookupQuery().ensure {
}
}
.done { contacts -> Void in
//Do something with the JSON info
print("Contacts Done")
handler(true,0.8,nil)
}
.catch(policy: .allErrors) { error in
print(error.localizedDescription)
}
}