CoreData表关联

来源：互联网发布：个人网络招商编辑：程序博客网时间：2024/06/10 13:00

- (void) _initManyTable{

//初始化模型

NSManagedObjectModel * model=[NSManagedObjectModelmergedModelFromBundles:nil];

//创建基础库协调器

NSPersistentStoreCoordinator * psc=[[NSPersistentStoreCoordinatoralloc] initWithManagedObjectModel:model];

//获取沙盒路径

NSString * path=[NSSearchPathForDirectoriesInDomains(NSDocumentDirectory,NSUserDomainMask, YES)firstObject];

path=[path stringByAppendingPathComponent:@"morestudent.sqlite"];

NSLog(@"%@",path);

//拼接URL

NSURL * url=[[NSURLalloc] initFileURLWithPath:path];

//为协调器添加基础库路径和基础库类型

[psc addPersistentStoreWithType:NSSQLiteStoreTypeconfiguration:nilURL:url options:nilerror:nil];

//创建上下文

NSManagedObjectContext *context=[[NSManagedObjectContextalloc] init];

context.persistentStoreCoordinator=psc;

NSError * error;

//************多表关联*************************************

//1、插入教师数据

// Teacher * teacher=[NSEntityDescription insertNewObjectForEntityForName:@"Teacher" inManagedObjectContext:context];

// teacher.name=@"laoshi";

//2、添加五个学生，并与表中已存在的上述老师建立联系

// NSFetchRequest * request=[[NSFetchRequest alloc] initWithEntityName:@"Teacher"];

// NSPredicate * pre=[NSPredicate predicateWithFormat:@"name='laoshi'"];

// request.predicate=pre;

// NSArray * array=[context executeFetchRequest:request error:nil];

// NSMutableSet * set=[NSMutableSet set];

// for (int i=0;i<5; i++) {

// Student * student=[NSEntityDescription insertNewObjectForEntityForName:@"Student" inManagedObjectContext:context];

// student.name=[NSString stringWithFormat:@"maoning%i",i];

// student.age=@(13+i);

// [set addObject:student];

// }

/// Teacher * teacher=[array firstObject];

// teacher.studentship=set;//一方建立了关系，另一方就不用再建立关系

//3、查询学生

// NSFetchRequest * request=[[NSFetchRequest alloc] initWithEntityName:@"Student"];

// NSArray * array=[context executeFetchRequest:request error:nil];

// for (Student * stu in array) {

// NSLog(@"%@,%@",stu.name,stu.teachership.name);

// NSLog(@"***************************");

// }

//4、查询老师以及每一位老师对应的学生

// NSFetchRequest * request=[[NSFetchRequest alloc] initWithEntityName:@"Teacher"];

// NSArray * array=[context executeFetchRequest:request error:nil];

// for (Teacher * tea in array) {

// NSLog(@"------------------------");

// NSLog(@"%@",tea.name);

// NSSet * set=tea.studentship;

// for (Student * stu in set) {

// NSLog(@"%@",stu.name);

// }

// NSLog(@"***************************");

// }

// *********************************

// 如果给已经存在的老师添加新的学生，原来的学生的关系会全部被顶替

// 正确的做法是：

// 1.>取出老师以及对应的学生

NSFetchRequest * request=[[NSFetchRequestalloc] initWithEntityName:@"Teacher"];

NSPredicate * pre=[NSPredicatepredicateWithFormat:@"name='laoshi'"];

request.predicate=pre;

NSArray * array=[context executeFetchRequest:request error:nil];

Teacher * teacher=[array firstObject];

NSMutableSet * set=[NSMutableSetsetWithSet:teacher.studentship];

// 2.>添加新学生

for (int i=0;i<5; i++) {

Student * student=[NSEntityDescriptioninsertNewObjectForEntityForName:@"Student"inManagedObjectContext:context];

student.name=[NSStringstringWithFormat:@"maoning%i",i];

student.age=@(13+i);

[setaddObject:student];

}

teacher.studentship=set;//一方建立了关系，另一方就不用再建立关系

//4、保存(相当于提交事务)

[contextsave:&error];

}

0 0