coreData数据操作

// 1. 建立模型文件
// 2. 建立CoreDataStack
// 3. 设置AppDelegate

接着

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

import CoreData

class CoreDataStack: NSObject {
    // MARK: - Properties
    let context: NSManagedObjectContext
    let coordinator: NSPersistentStoreCoordinator
    let model: NSManagedObjectModel
    let store: NSPersistentStore?
    
    // MARK: - Singleton
    static func defaultStack() -> CoreDataStack {
        return instance
    }
    
    fileprivate static let instance = CoreDataStack()
    
    fileprivate override init() {
        // 构建托管对象模型
        let bundle = Bundle.main
        let 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.default
        let 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...")
            }
        }
    }
}

接着实现数据操作

//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 = sno
        student.name = name
        student.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! NSDictionary
            let 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()
    }

总结：

增：

1:获取上下文

如：let context = CoreDataStack.defaultStack().context

2:构建实体对象

如：let student = NSEntityDescription.insertNewObject(forEntityName: "Student",

into: context) as! Student

3:设置相关属性

如： student.sno = sno

4:保存数据

如：CoreDataStack.defaultStack().saveContext()

 

修改，删除

1:获取上下文

2:构建抓取请求

如:let request = NSFetchRequest<NSFetchRequestResult>(entityName: "Student")

3:给抓去请求设置相关属性吧

如：

//相当于给它设置约束

request.predicate = NSPredicate(format: "name like 'a*'")

// 指定返回结果为字典（修改，删除一般不用设置这个）

request.resultType = .dictionaryResultType

4:执行抓取操作

do {

let students = (try context.fetch(request)) as! [Student]

for student in students {

//修改如：student.score = 100

//删除如：context.delete(student)

}

} catch {

print("Fetch failed...")

}

5:保存数据

 

查询

1:获取上下文

2:构建抓取请求

3:指定按照学号(sno)升序排列（其实此部可以省略）

let sort = NSSortDescriptor(key: "sno", ascending: true,

selector: #selector(NSString.localizedStandardCompare(_:)))

request.sortDescriptors = [sort]

4:执行抓取语句

do {

let students = (try context.fetch(request)) as! [Student]

for student in students {

print("(student.sno!), (student.name!), (student.score!)")

}

} catch {

print("Fetch failed...")

}

5:释放资源

 

统计

1:获取上下文

2:构建抓取请求

3:指定按照学号(sno)升序排列（其实此部可以省略）

let sort = NSSortDescriptor(key: "sno", ascending: true,

selector: #selector(NSString.localizedStandardCompare(_:)))

request.sortDescriptors = [sort]

4: 构建表达式(average是聚合函数，当然还有其他的)

如：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

5:将求平均值的表达式设置给request的属性

如request.propertiesToFetch = [description]

4:执行抓取语句

do {

let entries = (try context.fetch(request))

let result = entries.first! as! NSDictionary

let averageScore = result["AverageScore"]!

print("Average: (averageScore)")

} catch {

print("Fetch failed...")

}

5:释放资源

 

当然，这个只是一个例子而已，不是所有的统计例子都要那么复杂的

如下面这个例子

// 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...")

// }