Gists for the Medium post 'Paving A Road Between JSON And CoreData'

downloadPosts.swift

    private func downloadPosts(completion: @escaping ([PostData]?, Error?) ->Void) {
        let postsURL = URL(string: "https://jsonplaceholder.typicode.com/posts")!
        let downloadTask = urlSession.dataTask(with: postsURL) { data, response, error in
            if let error = error {
                completion(nil, error)
            }
            if let response = response as? HTTPURLResponse,
               !(200..<300).contains(response.statusCode) {
                return(completion(nil, PersistanceControllerError.Non200URLStatusCode(statusCode: response.statusCode)))
            }
            if let data = data {
                do {
                    let posts = try JSONDecoder().decode([PostData].self, from: data)
                    return(completion(posts, nil))
                } catch {
                    return(completion(nil, error))
                }
            }
        }
        downloadTask.resume()
    }

importPosts.swift

    private func importPosts(from posts:[PostData]) throws {
        let privateContext = newPrivateContext()
        privateContext.mergePolicy = NSMergeByPropertyObjectTrumpMergePolicy
        privateContext.undoManager = nil
        let batchSize = 10
        let numBatches = posts.count/batchSize
        
        for batchNumber in 0..<numBatches {
            let startIndex = batchNumber*batchSize
            let endIndex = batchNumber == (numBatches - 1) ? posts.count - 1 : (startIndex + batchSize)
            let dictionaryObjects = posts[startIndex..<endIndex].map({$0.propertyDictionary()})
            let batchInsertRequest = NSBatchInsertRequest(entityName: "Post", objects: dictionaryObjects)
            let fetchResult = try privateContext.execute(batchInsertRequest)
            if let batchInsertResult = fetchResult as? NSBatchInsertResult,
               let success = batchInsertResult.result as? Bool {
                if !success {
                    throw PersistanceControllerError.BatchInsertFailure
                }
            }
        }
    }

post_sample.json

[
  {
    "userId": 1,
    "id": 1,
    "title": "sunt aut facere repellat provident occaecati excepturi optio reprehenderit",
    "body": "quia et suscipit\nsuscipit recusandae consequuntur expedita et cum\nreprehenderit molestiae ut ut quas totam\nnostrum rerum est autem sunt rem eveniet architecto"
  },
  {
    "userId": 1,
    "id": 2,
    "title": "qui est esse",
    "body": "est rerum tempore vitae\nsequi sint nihil reprehenderit dolor beatae ea dolores neque\nfugiat blanditiis voluptate porro vel nihil molestiae ut reiciendis\nqui aperiam non debitis possimus qui neque nisi nulla"
  }
]

PostData.swift

struct PostData: Decodable {
    let userId: Int
    let id: Int
    let title: String
    let body: String
}

propertyDictionary.swift

extension PostData {
    func propertyDictionary() -> [String: Any] {
        //Used to translate JSON decoded struct to NSManagedObject Entity
        let mirror = Mirror(reflecting: self)
        var propertyDict: [String: Any] = [:]
        for child in mirror.children {
            if let propertyName = child.label {
                propertyDict[propertyName] = child.value
            }
        }
        return propertyDict
    }
}