CoreData object to JSON in Swift 3

Question

I'm struggling to get my CoreData objects into JSON so that I can use it to send to a web server.

This is how I currently fetch my objects from CoreData:

func fetchRecord() -> [Record] {

    do {
        records = try context.fetch(Record.fetchRequest())

    } catch {
        print("Error fetching data from CoreData")
    }
    return records
}

I am able to display this on to my tableView this way:

func tableView(_ tableView: UITableView, cellForRowAt indexPath: IndexPath) -> UITableViewCell {
    let cell = tableView.dequeueReusableCell(withIdentifier: "recordCell", for: indexPath) as! RecordCell

    cell.nameLbl.text = records[indexPath.row].name
    cell.quantityLbl.text = "Quantity: \(String(records[indexPath.row].quantity))"
    cell.dateLbl.text = dateString(date: records[indexPath.row].date)

    return cell
}

I have attempted to loop inside my request like this:

for rec in records {
    print(rec)
}

that gives out this:

I have read a lot about ways to achieve this but none of them seem to really be of beneficial to me. Most of the examples out there shows how to get JSON to CoreData and not the other way. Does anyone know any good tutorials or documentation that can help me achieve this?

vadian · Accepted Answer · 2021-03-29 11:17:55Z

15

In Swift 4+ you can take advantage of the Encodable protocol and add the functionality directly to your Core Data object.

Assuming your NSManagedObject subclass extension looks like

extension Record {
    
    @NSManaged public var date: Date
    @NSManaged public var name: String
    @NSManaged public var quantity: Int32
    @NSManaged public var synched: Bool
    @NSManaged public var uuid: String

   ...

Adopt Encodable

extension Record : Encodable {

and add

private enum CodingKeys: String, CodingKey { case date, name, quantity, synched, uuid }

public func encode(to encoder: Encoder) throws {
    var container = encoder.container(keyedBy: CodingKeys.self)
    try container.encode(date, forKey: .date)
    try container.encode(name, forKey: .name)
    try container.encode(quantity, forKey: .quantity)
    try container.encode(synched, forKey: .synched)
    try container.encode(uuid, forKey: .uuid)
}

Then you can easily encode the records to JSON

do {
    records = try context.fetch(Record.fetchRequest())
    let jsonData = try JSONEncoder().encode(records)
} catch {
    print("Error fetching data from CoreData", error)
}

edited Mar 29, 2021 at 11:17

answered May 10, 2018 at 10:37

vadian

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4 Comments

3h4x Over a year ago

Hmmm. I get "Instance method 'encode' requires that 'FetchedResults<Item>' conform to 'Encodable'"

vadian Over a year ago

You might have to cast FetchedResults<Item> to the static NSManagedObject subclass (Item)

Duck Over a year ago

Value of protocol type 'Any' cannot conform to 'Encodable'; only struct/enum/class types can conform to protocols

vadian Over a year ago

@Duck Codable relies on concrete types. You cannot en-/decode Any.

Mike_NotGuilty · Accepted Answer · 2018-05-10 10:19:14Z

13

Here the code as an extension. Based on KavyaKavita's answer.

extension NSManagedObject {
  func toJSON() -> String? {
    let keys = Array(self.entity.attributesByName.keys)
    let dict = self.dictionaryWithValues(forKeys: keys)
    do {
        let jsonData = try JSONSerialization.data(withJSONObject: dict, options: .prettyPrinted)
        let reqJSONStr = String(data: jsonData, encoding: .utf8)
        return reqJSONStr
    }
    catch{}
    return nil
  }
}

Usage:

let jsonString = YourCoreDataObject.toJSON()
print(jsonString)

answered May 10, 2018 at 10:19

Mike_NotGuilty

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Comments

KavyaKavita · Accepted Answer · 2017-09-15 11:11:48Z

6

You can convert your NSManageObject subclass object into dictionary by using following code

let record = recArray[index]
        let keys = Array(record.entity.attributesByName.keys)
        let dict = record.dictionaryWithValues(forKeys: keys)

After that you can use jsonserialization to convert that dictionary into json object

do{
        let jsonData = try JSONSerialization.data(withJSONObject: dict, options: .prettyPrinted)
        let reqJSONStr = String(data: jsonData, encoding: .utf8)
        print(reqJSONStr!)
    }catch{

    }

Hope this will help.

edited Sep 15, 2017 at 11:11

answered Sep 15, 2017 at 10:59

KavyaKavita

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5 Comments

Chace Over a year ago

Sorry, please see the updated title. Is there a way you could covert this into Swift?

Chace Over a year ago

Would you be able to explain where I'd use this code please?

KavyaKavita Over a year ago

please check swift version, as per your specification you want to send this Record object to webservice, for that you want to convert recort object into json. So just add this where you want to convert your coredata object inti json.

Chace Over a year ago

I am struggling to implement your example. Where are you getting the recArray? Could you please show me how it would work using my method. I assume the conversion takes place in the fetchRecord() function, but I'm just getting errors from this.

SouthernYankee65 Over a year ago

@Chace I'm sure you figured this out already, but in your OP you are fetching an array/list of records. That is what recArray is referring to in the above answer.

Vini App · Accepted Answer · 2017-09-17 19:37:22Z

1

If you want you can get the results in dictionary format from core data using below :

let fetchRequest = NSFetchRequest<NSFetchRequestResult>(entityName:"Record")
fetchRequest.resultType = .dictionaryResultType
do {
    records = try context.fetch(fetchRequest)
} catch {
    print("Error fetching data from CoreData")
}

answered Sep 17, 2017 at 19:37

Vini App

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1 Comment

Chace Over a year ago

I'm getting an error saying Cannot assign value of type '[Any]' to type '[Record]' and when I change it to: records = try context.fetch(fetchRequest) as! [Record] I'm getting this error Could not cast value of type 'NSKnownKeysDictionary1' (0x10639caf8) to Core_Data_App.Record' (0x1055a9360).

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