Parse large amount of JSON data with swift - ios

Question

I've got to fetch a large amount of data from a remote web server. I decided to use Alamofire for the HTTP request and Swifty JSON to parse JSON response. When the process ends I return back data to a UITableViewController and I feed my table view. Due to the size of JSON (1.5 MB), bind process to object model requires additional time.
Here an example of how I handle the process in my code:
Example of object model:
import Foundation
import SwiftyJSON
class Course {
var id: String!
var students: [JSON]
var hours: [JSON]
var related: [JSON]
init?(_ key: String, json: JSON) {
self.id = key
self.students = json["students"].arrayValue
self.calendar = json["calendar"].arrayValue
self.relatedCourses = json["related_courses"].arrayValue
}
}
Example of Alamofire request:
func fetchAllData(data: Data, completion: #escaping ([String:[String:Any]], [JSON]) -> ()) {) {
let url = "http://myapi/data" // includes courses
Alamofire.request(url, parameters: params)
.validate()
.responseJSON(queue: utilityQueue) {
response in
switch response.result {
case .success(let responseData):
let (results, order) = self.parseResults(json: JSON(responseData))
completion(results, order)
break
case .failure(let error):
AppDelegate.print(value: error)
break
}
}
}
Example of JSON parsing:
func parseResults(json: JSON) -> ([String:[String:Any]], [JSON]){
var results = [String:[String:Any]]()
results["courses"] = getCourses(from: json)
results["students"] = getStudents(from: json)
... I parse other elements here
return (results, order)
}
func getCourses(from json: JSON) -> [String:Course] {
var courses = [String:Course]()
for (key, data) : (String, JSON) in json["courses"] {
courses[key] = Course(key, json: data)!
}
return places
}
I used dictionaries in order to reduce time complexity to access elements. I've got lots of informations to join.
Here TableViewController methods:
override func viewDidAppear(_ animated: Bool) {
super.viewDidAppear(true)
// Call here fetch method
ResultsService().fetchResults(data: data, completion: {
(results, order) in
DispatchQueue.main.async {
self.courses = results["courses"]!
self.students = results["students"]!
...
self.spinner.stopAnimating()
self.tableView.reloadData()
}
})
}
func tableView(_ tableView: UITableView, cellForRowAt indexPath: IndexPath) -> UITableViewCell {
let cell = tableView.dequeueReusableCell(withIdentifier: "CourseCell", for: indexPath) as! CourseCell
let course = courses[orderedCourses[indexPath.row].stringValue] as! Course
let bestStudent = students[course.students[0].stringValue] as! Student
cell.courseName.text = course.name
cell.bestStudentScore.text = bestStudent.score
...
return cell
}
Everything is working fine, but I have to wait 3 or 4 seconds in order to get data displayed in table view. With a little bit of debugging I've pointed out that my bottleneck is binding JSON to objects. Do you have any suggestion useful to improve performances? I was thinking about something like: starting to parse JSON, return small chunks of data and display it in table view but I don't know exactly how to achieve this goal. I can't use pagination so I have to fetch whole data from web server and try to optimise everything from a client point of view. Thank you.