http://blog.csdn.net/fengsh998/article/details/8123392
在 CoreData中，多表查询上相对来说，没有SQL直观，但COREDATA的功能还是可以完成相关操作的。
多表查询，表与表之间肯定存在某种关系，如果对于类似外连接，左连接等操作，在COREDATA中就显得无力（请高手指教了）。
在上节中，介绍了一下的关系查询操作。
下面使用CoreData进行关系数据库的表与表之间的关系演示。
生成COREDATA和如何设置关系就不再详谈了，见之前的文章。
建立好的关系图：
一步步建立上面关系图：
先建立部门表，员工表，职位表，工资等级表，开户银行表
上面建立表之后，我们还需要建立表之间的关系
部门和员工之间的关系：1 V N
部门和职位的关系：1 V N
员工与职位的关系：多对一关系
员工与开户行：一个员工只能提供一个开户行，但一个开户行可以给多名员工进行开卡。所以关系为N V 1；
职位和工资等级：一个职位只对应一个工资等级；1V1
下面插入数据：
- (IBAction)onbtnclick:(id)sender { Department *dept = [NSEntityDescription insertNewObjectForEntityForName:@"Department" inManagedObjectContext:self.managedObjectContext]; dept.dp_deptname = @"HR"; Department *dept2 = [NSEntityDescription insertNewObjectForEntityForName:@"Department" inManagedObjectContext:self.managedObjectContext]; dept2.dp_deptname = @"DEV"; Department *dept3 = [NSEntityDescription insertNewObjectForEntityForName:@"Department" inManagedObjectContext:self.managedObjectContext]; dept3.dp_deptname = @"POD"; Salary *sy =[NSEntityDescription insertNewObjectForEntityForName:@"Salary" inManagedObjectContext:self.managedObjectContext]; sy.sy_level = @"D"; sy.sy_scale = [NSNumber numberWithDouble:0.1]; Salary *sy2 =[NSEntityDescription insertNewObjectForEntityForName:@"Salary" inManagedObjectContext:self.managedObjectContext]; sy2.sy_level = @"C"; sy2.sy_scale = [NSNumber numberWithDouble:0.15]; Salary *sy3 =[NSEntityDescription insertNewObjectForEntityForName:@"Salary" inManagedObjectContext:self.managedObjectContext]; sy3.sy_level = @"B"; sy3.sy_scale = [NSNumber numberWithDouble:0.4]; Salary *sy4 =[NSEntityDescription insertNewObjectForEntityForName:@"Salary" inManagedObjectContext:self.managedObjectContext]; sy4.sy_level = @"A"; sy4.sy_scale = [NSNumber numberWithDouble:0.8]; Post *pt= [NSEntityDescription insertNewObjectForEntityForName:@"Post" inManagedObjectContext:self.managedObjectContext]; pt.pt_name = @"行政专员"; pt.dept = dept; Post *pt2= [NSEntityDescription insertNewObjectForEntityForName:@"Post" inManagedObjectContext:self.managedObjectContext]; pt2.salary = sy3; pt2.pt_name = @"人事经理"; pt2.dept = dept; Post *pt3= [NSEntityDescription insertNewObjectForEntityForName:@"Post" inManagedObjectContext:self.managedObjectContext]; pt3.pt_name = @"开发工程师"; pt3.dept = dept2; pt3.salary = sy2; pt= [NSEntityDescription insertNewObjectForEntityForName:@"Post" inManagedObjectContext:self.managedObjectContext]; pt.pt_name = @"架构师"; pt.dept = dept2; pt= [NSEntityDescription insertNewObjectForEntityForName:@"Post" inManagedObjectContext:self.managedObjectContext]; pt.pt_name = @"项目经理"; pt.dept =dept2; Post *pt6= [NSEntityDescription insertNewObjectForEntityForName:@"Post" inManagedObjectContext:self.managedObjectContext]; pt6.pt_name = @"测试工程师"; pt6.dept = dept2; pt6.salary = sy; pt= [NSEntityDescription insertNewObjectForEntityForName:@"Post" inManagedObjectContext:self.managedObjectContext]; pt.pt_name = @"销售代表"; pt.dept = dept3; pt= [NSEntityDescription insertNewObjectForEntityForName:@"Post" inManagedObjectContext:self.managedObjectContext]; pt.pt_name = @"销售经理"; pt.dept = dept3; Post *pt9= [NSEntityDescription insertNewObjectForEntityForName:@"Post" inManagedObjectContext:self.managedObjectContext]; pt9.pt_name = @"大客户经理"; pt9.dept = dept3; pt9.salary = sy4; Bank *bk = [NSEntityDescription insertNewObjectForEntityForName:@"Bank" inManagedObjectContext:self.managedObjectContext]; bk.bk_name = @"招行"; bk.bk_address = @"广州"; Bank *bk2 = [NSEntityDescription insertNewObjectForEntityForName:@"Bank" inManagedObjectContext:self.managedObjectContext]; bk2.bk_name = @"浦发"; bk2.bk_address = @"上海"; Bank *bk3 = [NSEntityDescription insertNewObjectForEntityForName:@"Bank" inManagedObjectContext:self.managedObjectContext]; bk3.bk_name = @"工行"; bk3.bk_address = @"深圳"; Employee *em = [NSEntityDescription insertNewObjectForEntityForName:@"Employee" inManagedObjectContext:self.managedObjectContext]; em.em_age = [NSNumber numberWithInt:20]; em.em_name = @"张三"; em.em_sex = [NSNumber numberWithInt:1]; em.em_bankcardid = @"46326587439043"; em.dept = dept2; em.post = pt3; em.bank = bk2; em = [NSEntityDescription insertNewObjectForEntityForName:@"Employee" inManagedObjectContext:self.managedObjectContext]; em.em_age = [NSNumber numberWithInt:18]; em.em_name = @"李四"; em.em_sex = [NSNumber numberWithInt:2]; em.em_bankcardid = @"32565443246567"; em.dept = dept; em.post = pt2; em.bank = bk3; em = [NSEntityDescription insertNewObjectForEntityForName:@"Employee" inManagedObjectContext:self.managedObjectContext]; em.em_age = [NSNumber numberWithInt:26]; em.em_name = @"欧阳"; em.em_sex = [NSNumber numberWithInt:2]; em.em_bankcardid = @"14354654656767"; em.dept = dept3; em.post = pt9; em.bank = bk3; em = [NSEntityDescription insertNewObjectForEntityForName:@"Employee" inManagedObjectContext:self.managedObjectContext]; em.em_age = [NSNumber numberWithInt:22]; em.em_name = @"欧阳"; em.em_sex = [NSNumber numberWithInt:2]; em.em_bankcardid = @"9873429837433"; em.dept = dept2; em.post = pt6; em.bank = bk3; [self.managedObjectContext save:nil]; }
数据库中数据:
1、查询开发部门中名为张三的工资等级
NSEntityDescription * emEty = [NSEntityDescription entityForName:@"Employee" inManagedObjectContext:self.managedObjectContext];
NSFetchRequest *frq = [[[NSFetchRequest alloc]init]autorelease]; [frq setEntity:emEty]; NSPredicate * cdt = [NSPredicate predicateWithFormat:@"em_name = %@",@"张三"]; [frq setPredicate:cdt]; NSArray *objs =[self.managedObjectContext executeFetchRequest:frq error:nil]; //NSLog(@"%i",[objs count]); NSLog(@"%@",((Employee*)[objs objectAtIndex:0]).post.salary.sy_level);
2、查询运维部名为欧阳的工资等级及开户银行
NSEntityDescription * entity = [NSEntityDescription entityForName:@"Employee" inManagedObjectContext:self.managedObjectContext]; NSFetchRequest *fetch = [[[NSFetchRequest alloc]init]autorelease]; [fetch setEntity:entity]; NSPredicate * qcmd = [NSPredicate predicateWithFormat:@"em_name = %@ ",@"欧阳"]; [fetch setPredicate:qcmd]; NSArray * obs = [self.managedObjectContext executeFetchRequest:fetch error:nil]; NSPredicate * filter = [NSPredicate predicateWithFormat:@"dept.dp_deptname = %@",@"POD"]; NSArray * ret = [obs filteredArrayUsingPredicate:filter]; //从数组中进行过滤。 NSLog(@"%@",((Employee*)[ret objectAtIndex:0]).post.salary.sy_level);
多表查询主要就在于表之间建立好相关的关联关系（relationship），其次就是充分的使用NSPredicate 这个查询条件来进行过滤。