5- coreData基本扩展(保存NSArray)

一.文章概要

关于NSArray的保存,研究了好久,最终只试验成功了这一种方案,感觉有点不合逻辑,譬如重新创建一个和实体对应的对象类.大家要是有更好的方案的话,希望能够告诉我下,不胜感激!!!

二.准备工作(关于NSKeyedArchiver)

三.新增加保存NSArray的属性

第一步,在实体中增加属性

第二步,生成新的"NSManagedObject"子类文件

四.创建需要保存的对象类

还有一点我要提到的是,在最开始的试验保存NSArray时候,想要直接保存上述NSManagedObject Subclass子类,到那时各种尝试始终不行,不是保存的时候报错,就是读取的时候报错

重新创建一个新的对应全部属性的NSObject类

所以同时还需要实现NSCoding 协议中的两个方法，分别是"encodeWithCoder"和"initWithCoder"

//
//  BookInfo.h
//  fmdb
//
//  Created by 李龙 on 16/1/5.
//  Copyright © 2016年 李龙. All rights reserved.
//

#import <Foundation/Foundation.h>
#import "Student.h"

@interface BookInfo : NSObject

@property (nonatomic, assign) NSNumber *bookID;
@property (copy, nonatomic) NSString *bookName;
@property (strong,nonatomic) Student *student;

@end

//
//  BookInfo.m
//  fmdb
//
//  Created by 李龙 on 16/1/5.
//  Copyright © 2016年 李龙. All rights reserved.
//

#import "BookInfo.h"

@implementation BookInfo

- (void) encodeWithCoder: (NSCoder *)coder
{
[coder encodeObject:self.bookID forKey:@"bookID"];
//    [coder encodeObject:self.bookName forKey:@"bookName"];
[coder encodeObject:self.student forKey:@"student"];
}

- (id)initWithCoder:(NSCoder *)aDecoder{
if (self = [super init]) {

self.bookID = [aDecoder decodeObjectForKey:@"bookID"];
//        self.student = [aDecoder decodeObjectForKey:@"student"];
self.bookName = [aDecoder decodeObjectForKey:@"bookName"];
}
return self;
}

@end

注意:如果你要在BookInfo的对象中保存stduent这个属性,那么按照这种方法,你还需要在创建一个平常的和实体Student对应的Student的对象类

五.保存和读取NSArray

保存NSArray

//插入数据
- (IBAction)insertData{
NSLog(@"插入数据");

//====== 3'
//第一组数据
Student *student = [NSEntityDescription insertNewObjectForEntityForName:@"Student" inManagedObjectContext:self.managedContext];
student.name = @"张三2";
student.id = @(11);

BookInfo *book =  [[BookInfo alloc] init];
book.bookID = @(121);
book.bookName = @"<老人与海2>";
//        book.student = student;
//        student.book = book;

BookInfo *book1 =  [[BookInfo alloc] init];
book1.bookID = @(121);
book1.bookName = @"<老人与海2>";
//        book1.student = student;

student.booksArray = [NSKeyedArchiver archivedDataWithRootObject:@[book,book1]];

//第二组数据
Student *student2 = [NSEntityDescription insertNewObjectForEntityForName:@"Student" inManagedObjectContext:self.managedContext];
student2.name = @"李四2";
student2.id = @(23);

BookInfo *book2 = [[BookInfo alloc] init];
book2.bookID = @(242);
book2.bookName = @"<飞鸟集2222>";
//        book2.student = student;
//        student2.book = book2;

BookInfo *book22 =  [[BookInfo alloc] init];
book22.bookID = @(242);
book22.bookName = @"<飞鸟集22222>";
book22.student = student;

student2.booksArray = [NSKeyedArchiver archivedDataWithRootObject:@[book2,book22]];

//保存,用 save 方法
NSError *error = nil;
BOOL success = [self.managedContext save:&error];
if (!success) {
[NSException raise:@"访问数据库错误" format:@"%@",[error localizedDescription]];
}
}

读取NSArray

//读取数据库文件
- (IBAction)readData{
NSLog(@"读取数据");
dispatch_async(dispatch_get_main_queue(), ^{

// 初始化一个查询请求
NSFetchRequest *request = [[NSFetchRequest alloc] init];
// 设置要查询的实体
request.entity = [NSEntityDescription entityForName:@"Student" inManagedObjectContext:self.managedContext];

//以上代码简写成下边
//        NSFetchRequest *request = [NSFetchRequest fetchRequestWithEntityName:@"Student"];

// 设置排序（按照age降序）
NSSortDescriptor *sort = [NSSortDescriptor sortDescriptorWithKey:@"id" ascending:NO];
request.sortDescriptors = [NSArray arrayWithObject:sort];

// 执行请求
NSError *error = nil;
NSArray *objs = [self.managedContext executeFetchRequest:request error:&error];
if (error) {
[NSException raise:@"查询错误" format:@"%@", [error localizedDescription]];
}

NSLog(@"-----------------------------------");
// 遍历数据

for (Student *stu in objs) {
//获取书的数组
NSArray *bookArr = [NSKeyedUnarchiver unarchiveObjectWithData:stu.booksArray];
NSLog(@"%@",bookArr);
for (BookInfo *book in bookArr) {
NSLog(@"bookInfo:%zd-----%@-----%@",book.bookID,book.bookName,book.student);
}
}
});
}

六.小结