Monday, 10 September 2018

Codable with CoreData

Swift define standard approach to data encoding and decoding which combines the Encodable and Decodable protocols that is called Codable.

In this block I illustrated Codable using API parse and store into CoreData.
First you need to create entity called "List" and create attribute(id,user_id,title,body) like below

CoreData
List Entity

and then create NSManageObject subclass for List entity.
Now create encode and decode method like below

import Foundation
import CoreData

@objc(List)
public class List: NSManagedObject,Codable {
    
    ///From api response key if changed
    enum apiKey: String, CodingKey {
        case id
        case user_id = "userId"
        case title
        case body
    }

    // MARK: - Decodable
    required convenience public init(from decoder: Decoder) throws {
        
        ///Fetch context for codable
        guard let codableContext = CodingUserInfoKey.init(rawValue: "context"),
            let manageObjContext = decoder.userInfo[codableContext] as? NSManagedObjectContext,
            let manageObjList = NSEntityDescription.entity(forEntityName: "List", in: manageObjContext) else {
                fatalError("failed")
        }
        
        self.init(entity: manageObjList, insertInto: manageObjContext)
        
        let container = try decoder.container(keyedBy: apiKey.self)
        self.user_id = try container.decodeIfPresent(Int64.self, forKey: .user_id) ?? 0
        self.id = try container.decodeIfPresent(Int64.self, forKey: .id) ?? 0
        self.title = try container.decodeIfPresent(String.self, forKey: .title)
        self.body = try container.decodeIfPresent(String.self, forKey: .body)
    }
    
    // MARK: - encode
    public func encode(to encoder: Encoder) throws {
        var container = encoder.container(keyedBy: apiKey.self)
        try container.encode(user_id, forKey: .user_id)
        try container.encode(id, forKey: .id)
        try container.encode(title, forKey: .title)
        try container.encode(body, forKey: .body)
    }

}

Now send server request and parse response using Codable and store into CoreData.

///get data from api
    func getListData()  {
        guard let listURL = URL(string: "https://jsonplaceholder.typicode.com/posts/")else {
            return
        }
        URLSession.shared.dataTask(with: listURL){
            (data,response,error) in
            guard let jsonData = data else { return }
            DispatchQueue.main.async {
                self.parseResponse(forData: jsonData)
            }
        }.resume()
    }
    
    ///parse response using decodable and store data 
    func parseResponse(forData jsonData : Data)  {
        do {
            guard let codableContext = CodingUserInfoKey.init(rawValue: "context") else {
                fatalError("Failed context")
            }
            
            let manageObjContext = appDelegate.persistentContainer.viewContext
            let decoder = JSONDecoder()
            decoder.userInfo[codableContext] = manageObjContext
            // Parse JSON data
            _ = try decoder.decode([List].self, from: jsonData)
            ///context save
            try manageObjContext.save()
            UserDefaults.standard.set(true, forKey: "isAllreadyFetch")
            self.fetchLocalData()
        } catch let error {
            print("Error ->\(error.localizedDescription)")
            self.errorMessage(error.localizedDescription)
        }
    }

And fetch data like below 

    ///Local data fetch from core data
    func fetchLocalData()  {
        let manageObjContext = appDelegate.persistentContainer.viewContext
        let fetchRequest = NSFetchRequest<List>(entityName: "List")
        ///Sort by id
        let sortDescriptor = NSSortDescriptor(key: "id", ascending: true)
        fetchRequest.sortDescriptors = [sortDescriptor]
        do {
            self.arrayOfList = try manageObjContext.fetch(fetchRequest)
        } catch let error {
            print(error)
            self.errorMessage(error.localizedDescription)
        }
    }

The sample code for illustrated in this post is available on GitHub
Thank you.

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