Guidance on Core Data with Swift 3 - ios

Question

Not looking for code (wouldn't hurt though) just looking to know how I should go about this. I have an app which is like a blog reader. I have information in a MYSQL database which is taken with JSON, placed in a jsonArray and then placed in an array to be shown in a table view. In that table view I generally have all my objects in 1 section. Each row/object has a button when clicked it moves that row into another section. I also have a search controller to search through the main section (Section 1).
How do I save the order or position of the rows to Core Data?
For example: I have 0 rows in Section 0 and 5 rows in Section 1, I click the button on one of the rows in Section 1 and it moves that row to Section 0, now Section 0 has 1 row while Section 1 has 4 rows. How do I save this new tableview order to Core Data? I just want to save the rows positions, so the app remembers which section that selected row was in.
Do I save the indexPath of the row in the section?
When adding an entity and attributes, what do I use to save?
Also, its a mysql reader so when the tableview is reloaded and a new content is added, will it still show since the tableview will be reading from core data?
I'm learning Core Data (Swift 3 code) but just having trouble using it for this app.
Thank you for helping out!

Answer 1

Use UserDefaults to save the ordering data if you don't need to save the whole data from MySQL database. Define a class only contains dataId and indexPath:
class DataOrdering: NSObject, NSCoding {
var indexPath: IndexPath?
var dataId: String?
init(dataId: String, indexPath: IndexPath) {
super.init()
self.dataId = dataId
self.indexPath = indexPath
}
required init(coder aDecoder: NSCoder) {
if let dataId = aDecoder.decodeObject(forKey: "dataId") as? String {
self.dataId = dataId
}
if let indexPath = aDecoder.decodeObject(forKey: "indexPath") as? IndexPath {
self.indexPath = indexPath
}
}
func encode(with aCoder: NSCoder) {
aCoder.encode(dataId, forKey: "dataId")
aCoder.encode(indexPath, forKey: "indexPath")
}
func save(defaults key: String) -> Bool {
let defaults = UserDefaults.standard
let savedData = NSKeyedArchiver.archivedData(withRootObject: self)
defaults.set(savedData, forKey: key)
return defaults.synchronize()
}
convenience init?(defaults key: String) {
let defaults = UserDefaults.standard
if let data = defaults.object(forKey: key) as? Data,
let obj = NSKeyedUnarchiver.unarchiveObject(with: data) as? DataOrdering,
let dataId = obj.dataId,
let indexPath = obj.indexPath {
self.init(dataId: dataId, indexPath: indexPath)
} else {
return nil
}
}
class func allSavedOrdering(_ maxRows: Int) -> [Int: [DataOrdering]] {
var result: [Int: [DataOrdering]] = [:]
for section in 0...1 {
var rows: [DataOrdering] = []
for row in 0..<maxRows {
let indexPath = IndexPath(row: row, section: section)
if let ordering = DataOrdering(defaults: indexPath.defaultsKey) {
rows.append(ordering)
}
rows.sort(by: { $0.indexPath! < $1.indexPath! })
}
result[section] = rows
}
return result
}
}
Playground sample:
let data = DataOrdering(dataId: "1", indexPath: IndexPath(row: 0, section: 0))
let savedData = NSKeyedArchiver.archivedData(withRootObject: data)
let obj = NSKeyedUnarchiver.unarchiveObject(with: savedData) as? DataOrdering
obj?.dataId // print: "1"
obj?.indexPath // print: [0,0]
Use save function to save with a "key" and read it back by DataOrdering(defaults: "key")
UPDATED
Added codes for a view controller to use this class:
extension IndexPath {
var defaultsKey: String { return "data_ordering_\(section)_\(row)" }
}
class ViewController: UITableViewController {
var data: [Any]?
var items: [[Any]]?
func fetchData() {
// request from remote or local
data = [1, 2, 3, "a", "b", "c"] // sample data
// Update the items to first section has 0 elements,
// and place all data in section 1
items = [[], data ?? []]
// apply ordering
applySorting() { "\($0)" }
// save ordering
saveSorting() { "\($0)" }
// refresh the table view
tableView.reloadData()
}
func applySorting(_ dataIdBlock: (Any) -> String) {
// get all saved ordering
guard let data = self.data else { return }
let ordering = DataOrdering.allSavedOrdering(data.count)
var result: [[Any]] = [[], []]
for (section, ordering) in ordering {
guard section <= 1 else { continue } // make sure the section is 0 or 1
let rows = data.filter({ obj -> Bool in
return ordering.index(where: { $0.dataId == .some(dataIdBlock(obj)) }) != nil
})
result[section] = rows
}
self.items = result
}
func saveSorting(_ dataIdBlock: (Any) -> String) {
guard let items = self.items else { return }
for (section, rows) in items.enumerated() {
for (row, item) in rows.enumerated() {
let indexPath = IndexPath(row: row, section: section)
let dataId = dataIdBlock(item)
let ordering = DataOrdering(dataId: dataId, indexPath: indexPath)
ordering.save(defaults: indexPath.defaultsKey)
}
}
}
#IBAction func buttonMoveToSectionTapped(_ sender: UIButton) {
// if the sender's tag is row index
// or you can get indexPath by tableView.indexPath(for: cell) function too
let row = sender.tag
// move this item from section 1 to section 0 (last position)
if let item = items?[1].remove(at: row) {
items?[0].append(item)
}
// Save all sorting
saveSorting() { "\($0)" }
tableView.reloadData() // refresh table view
}
override func numberOfSections(in tableView: UITableView) -> Int {
return self.items?.count ?? 0
}
override func tableView(_ tableView: UITableView, numberOfRowsInSection section: Int) -> Int {
return self.items?[section].count ?? 0
}
}