//
//  CoreDataStack.swift
//  CoreDataStackDemo
//
//  Created by wangbiao on 15/10/29.
//  Copyright © 2015年 wangbiao. All rights reserved.
//

import CoreDataclass CoreDataStack: NSObject {// MARK: - Properties
    let context: NSManagedObjectContextlet coordinator: NSPersistentStoreCoordinatorlet model: NSManagedObjectModellet store: NSPersistentStore?// MARK: - Singletonstatic func defaultStack() -> CoreDataStack {return instance}fileprivate static let instance = CoreDataStack()fileprivate override init() {// 构建托管对象模型let bundle = Bundle.mainlet modelURL = bundle.url(forResource: "Test", withExtension: "momd")!model = NSManagedObjectModel(contentsOf: modelURL)!// 构建持久化存储助理coordinator = NSPersistentStoreCoordinator(managedObjectModel: model)// 构建托管对象上下文，并且将助理连接到上下文context = NSManagedObjectContext(concurrencyType: .mainQueueConcurrencyType)context.persistentStoreCoordinator = coordinator// 构建持久化存储let manager = FileManager.defaultlet urls = manager.urls(for: .documentDirectory, in: .userDomainMask)let documentsURL = urls.first!let storeURL = documentsURL.appendingPathComponent("Test")store = (try! coordinator.addPersistentStore(ofType: NSSQLiteStoreType,configurationName: nil, at: storeURL, options: nil))}// MARK: - Function
    func saveContext () {if context.hasChanges {do {try context.save()} catch {print("Save failed...")}}}
}

//新增数据
func insertStudent(sno: String, name: String, score: Int) {// 获取上下文（也就是从”coreData基础“里面的那个类里面获取）let context = CoreDataStack.defaultStack().context// 构建实体对象let student = NSEntityDescription.insertNewObject(forEntityName: "Student",into: context) as! Student// 设置相关属性student.sno = snostudent.name = namestudent.score = score as NSNumber?}// 查询数据
    func fetchStudents() {// 获取上下文let context = CoreDataStack.defaultStack().context// 构建抓取请求let request = NSFetchRequest<NSFetchRequestResult>(entityName: "Student")// 指定按照学号(sno)升序排列let sort = NSSortDescriptor(key: "sno", ascending: true,selector: #selector(NSString.localizedStandardCompare(_:)))request.sortDescriptors = [sort]// 构建查询条件
//        request.predicate = NSPredicate(format: "score > 60")
//        request.predicate = NSPredicate(format: "name like 'a*'")do {let students = (try context.fetch(request)) as! [Student]for student in students {print("\(student.sno!), \(student.name!), \(student.score!)")}} catch {print("Fetch failed...")}}// 统计信息
    func countStudents() {
//        // 1. 统计分数大于90的人数
//
//        // 获取上下文
//        let context = CoreDataStack.defaultStack().context
//
//        // 构建抓取请求
//        let request = NSFetchRequest(entityName: "Student")
//        request.predicate = NSPredicate(format: "score > 90")
//        request.resultType = .CountResultType
//
//        do {
//            let entries = (try context.executeFetchRequest(request))
//            let count = entries.first!.integerValue
//            print("Count: \(count)")
//        } catch {
//            print("Fetch failed...")
//        }// 2. 计算平均分数// 获取上下文let context = CoreDataStack.defaultStack().context// 构建抓取请求let request = NSFetchRequest<NSFetchRequestResult>(entityName: "Student")request.resultType = .dictionaryResultType // 指定返回结果为字典// 构建表达式let description = NSExpressionDescription()description.name = "AverageScore"let args = [NSExpression(forKeyPath: "score")]description.expression = NSExpression(forFunction: "average:", arguments: args)description.expressionResultType = .floatAttributeType // 指定返回值类型// 将求平均值的表达式设置给request的属性request.propertiesToFetch = [description]do {let entries = (try context.fetch(request))let result = entries.first! as! NSDictionarylet averageScore = result["AverageScore"]!print("Average: \(averageScore)")} catch {print("Fetch failed...")}}// 修改数据
    func updateStudents() {// 获取上下文let context = CoreDataStack.defaultStack().context// 构建抓取请求let request = NSFetchRequest<NSFetchRequestResult>(entityName: "Student")request.predicate = NSPredicate(format: "name like 'a*'")do {let students = (try context.fetch(request)) as! [Student]for student in students {student.score = 100}} catch {print("Fetch failed...")}// 保存
        CoreDataStack.defaultStack().saveContext()// 备注: 批量更新 & 异步操作 ???
    }// 删除数据
    func deleteStudents() {// 获取上下文let context = CoreDataStack.defaultStack().context// 构建抓取请求let request = NSFetchRequest<NSFetchRequestResult>(entityName: "Student")request.predicate = NSPredicate(format: "score < 60")do {let students = (try context.fetch(request)) as! [Student]for student in students {context.delete(student)}} catch {print("Fetch failed...")}// 保存
        CoreDataStack.defaultStack().saveContext()}