如何基于双向RelationShip从核心数据中获取数据？

Question

在我的示例应用程序中，我有两个实体称为帐户和客户

为此，我创建了两个NSManagedObject子类

核心数据实体http：//i.stack。

imgur.com/zmt1N.png

现在，我完全不知道它的正确性还是正确性，我必须保存到这些核心数据实体并检索诸如“ 在帐户表中拥有三个以上帐户的客户 ”之类的详细信息

期待一些详细的解释。 提前致谢

Answer 1

使用NSPredicate

https://developer.apple.com/library/ios/documentation/Cocoa/Reference/Foundation/Classes/NSPredicate_Class/index.html

一个简单的示例，其中“搜索”名称不区分大小写的字符串：

NSFetchRequest *request = [NSFetchRequest fetchRequestWithEntityName:@"customer"];

request.predicate = [NSPredicate predicateWithFormat:@"name LIKE[c] %@", @"Amazon"];

NSArray *matches = [self.managedObjectContext executeFetchRequest:request error:nil];

根据上面链接的NSPredicate类参考：

您可以为关系创建谓词，例如：

group.name，例如“ work *”

所有儿童年龄> 12岁

任何年龄> 12岁的儿童

Answer 2

这是我期望做的。 谢谢您的帮助

-(void)savingDummyDatas
{

    NSManagedObjectContext *context = [self managedObjectContext];
    NSEntityDescription *entityDesc = [NSEntityDescription entityForName:@"Customer" inManagedObjectContext:context];
        NSFetchRequest *request = [[NSFetchRequest alloc] init];
    [request setEntity:entityDesc];
    NSError *error;
    NSArray *objects = [context executeFetchRequest:request error:&error];

//execution starting time
    NSDate *methodStart = [NSDate date];
// 
    if ([objects count] == 0)
    {

#pragma mark - Entity Insertion With Relation

//for (int i=1; i<=100000; i++) {
        //1

        Customer *custObj1 = [NSEntityDescription insertNewObjectForEntityForName:@"Customer" inManagedObjectContext:context];
        custObj1.name = @"Yeswant";
        // add accoutns for customer

        Accounts *acObj1 = [NSEntityDescription insertNewObjectForEntityForName:@"Accounts" inManagedObjectContext:context];
        acObj1.accountNumber = @"001";

        [custObj1 addCust_relationObject:acObj1];

        Accounts *acObj2 = [NSEntityDescription insertNewObjectForEntityForName:@"Accounts" inManagedObjectContext:context];
        acObj2.accountNumber = @"002";
        [custObj1 addCust_relationObject:acObj2];

        Accounts *acObj3 = [NSEntityDescription insertNewObjectForEntityForName:@"Accounts" inManagedObjectContext:context];
        acObj3.accountNumber =@"003";
        [custObj1 addCust_relationObject:acObj3];

        Accounts *acObj4 = [NSEntityDescription insertNewObjectForEntityForName:@"Accounts" inManagedObjectContext:context];
        acObj4.accountNumber =@"004";
        [custObj1 addCust_relationObject:acObj4];

    //2

        Customer *custObj2 = [NSEntityDescription insertNewObjectForEntityForName:@"Customer" inManagedObjectContext:context];
        custObj2.name= @"Bharath";
        // add accoutns for customer

        Accounts *acObj01 = [NSEntityDescription insertNewObjectForEntityForName:@"Accounts" inManagedObjectContext:context];
        acObj01.accountNumber = @"010";
        [custObj2 addCust_relationObject:acObj01];

        Accounts *acObj02 = [NSEntityDescription insertNewObjectForEntityForName:@"Accounts" inManagedObjectContext:context];
        acObj02.accountNumber = @"011";
        [custObj2 addCust_relationObject:acObj02];

        Accounts *acObj03 = [NSEntityDescription insertNewObjectForEntityForName:@"Accounts" inManagedObjectContext:context];
        acObj03.accountNumber =@"101";
        [custObj2 addCust_relationObject:acObj03];

//3
        Customer *custObj3 = [NSEntityDescription insertNewObjectForEntityForName:@"Customer" inManagedObjectContext:context];
        custObj3.name = @"Ansal";
        // add accoutns for customer

        Accounts *acObj001 = [NSEntityDescription insertNewObjectForEntityForName:@"Accounts" inManagedObjectContext:context];
        acObj001.accountNumber = @"001";

        [custObj3 addCust_relationObject:acObj001];

        Accounts *acObj002 = [NSEntityDescription insertNewObjectForEntityForName:@"Accounts" inManagedObjectContext:context];
        acObj002.accountNumber = @"002";
        [custObj3 addCust_relationObject:acObj002];

        Accounts *acObj003 = [NSEntityDescription insertNewObjectForEntityForName:@"Accounts" inManagedObjectContext:context];
        acObj003.accountNumber =@"003";
        [custObj3 addCust_relationObject:acObj003];

        Accounts *acObj004 = [NSEntityDescription insertNewObjectForEntityForName:@"Accounts" inManagedObjectContext:context];
        acObj004.accountNumber =@"004";
        [custObj3 addCust_relationObject:acObj004];


    //4

        Customer *custObj4 = [NSEntityDescription insertNewObjectForEntityForName:@"Customer" inManagedObjectContext:context];
        custObj4.name = @"Vijeesh";
        // add accoutrns for customer

        Accounts *acObj0001 = [NSEntityDescription insertNewObjectForEntityForName:@"Accounts" inManagedObjectContext:context];
        acObj0001.accountNumber = @"010";
        [custObj4 addCust_relationObject:acObj0001];

        Accounts *acObj0002 = [NSEntityDescription insertNewObjectForEntityForName:@"Accounts" inManagedObjectContext:context];
        acObj0002.accountNumber = @"011";
        [custObj4 addCust_relationObject:acObj0002];

        Accounts *acObj0003 = [NSEntityDescription insertNewObjectForEntityForName:@"Accounts" inManagedObjectContext:context];
        acObj0003.accountNumber =@"101";
        [custObj4 addCust_relationObject:acObj0003];
[context save:nil];



   }

检索这些保存的数据并使用谓词进行过滤或获取

-(void)fetchCoreDAta
{


    NSFetchRequest *fetchRequest = [[NSFetchRequest alloc] init];

    NSFetchRequest *fetchRequest1 = [[NSFetchRequest alloc] init];

    NSEntityDescription *entity = [NSEntityDescription entityForName:@"Customer" inManagedObjectContext:self.managedObjectContext];

    NSEntityDescription *entityAccounts = [NSEntityDescription entityForName:@"Accounts" inManagedObjectContext:self.managedObjectContext];

    [fetchRequest setEntity:entity];

    [fetchRequest1 setEntity:entityAccounts];

  //  [fetchRequest1 setEntity:entity];


#pragma mark - using predicates for fetching customer name who having three accounts

    NSPredicate *predicate =[NSPredicate predicateWithFormat:@"cust_relation.@count == 4"];
  //  NSPredicate *predicate1 =   [NSPredicate predicateWithFormat:@"ANY account_relation.name LIKE[c] 'Vijeesh'"];

       NSPredicate *predicate1 =   [NSPredicate predicateWithFormat:@"ANY account_relation.name like 'Vijeesh'"];


    NSString *value1 =@"Ansal";
    NSString *value2 =@"Vijeesh";



  //  NSPredicate *predicate2 = [NSPredicate predicateWithFormat:@"(name == %@) AND (SUBQUERY(subs, $x, $x.numbervalue == %@ or $x.numbervalue == %@).@count > 0)", @"Yeswant", value1, value2] ;

   [fetchRequest setPredicate:predicate];

   [fetchRequest1 setPredicate:predicate1];



    NSError *error = nil;


    NSArray *result = [self.managedObjectContext executeFetchRequest:fetchRequest error:&error];


    NSArray *resultAccounts = [self.managedObjectContext executeFetchRequest:fetchRequest1 error:&error];

    if (error)
    {
        NSLog(@"Unable to execute fetch request.");
        NSLog(@"%@, %@", error, error.localizedDescription);

    }
    else
    {
        NSLog(@"%@", result);
        NSLog(@"accounts:%@",resultAccounts);

        NSMutableArray * userNAmeArray = [result valueForKey:@"name"];

        NSMutableArray * accountsnumberArray = [resultAccounts valueForKey:@"accountNumber"];

        NSLog(@"names:%@",userNAmeArray);
        NSLog(@"acnums:%@",accountsnumberArray);


    }
     }