Question

我是IOS开发的新手，在使用关系

时特别使用核心数据时遇到问题

如您所见，我有树实体，我想要做的是在特定用户食用食物时将数据插入CredentialsFood实体

所以我试图使用以下代码插入

    // adding to credetialsFood Entity
NSManagedObjectContext *context1 = [appD managedObjectContext];
CredentialsFood *credentialsFood = (CredentialsFood *)        [NSEntityDescription insertNewObjectForEntityForName:@"CredentialsFood"   inManagedObjectContext:context1];
NSDate *currentDate = [NSDate date];
credentialsFood.toFood.food_id = item_id;
credentialsFood.toCred.email = @"123";
credentialsFood.date = currentDate;


// here's where the actual save happens,
if(![context1 save:&errorCoreData]){
    NSLog(@"Problem saving: %@",[error localizedDescription]);
}
else{
    NSLog(@"Food date Saved");
}

代码工作正常但是在检索时我尝试例如获取所有CredentialsFood.date，其中Credentials.email = 123 我什么都没收到

我真的不知道我做错了这是要检索的代码

NSManagedObjectContext *context2 = [appD managedObjectContext];

NSEntityDescription *foodEntity =[NSEntityDescription entityForName:@"Credentials" inManagedObjectContext:context2];

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

NSError *error2 = nil;
NSString * userid =@"123";

NSPredicate *foodPredicate = [NSPredicate predicateWithFormat:@"(email contains[cd] %@)",userid];

[request setEntity:foodEntity];
[request setPredicate:foodPredicate];

NSManagedObject *matches = nil;
NSArray *objects = [context executeFetchRequest:request error:&error2];


if([objects count]== 0){
    NSLog (@"no matches found");

}
else {
    //NSLog(@"aasdasdad %@", objects);
    matches = [objects objectAtIndex:0];
    NSLog(@"bb %@",[matches valueForKey:@"name"]);
    NSLog(@"bb %@",[matches valueForKey:@"email"]);
    NSLog(@"bb %@",[matches valueForKey:@"password"]);
    //NSLog(@"hhhhhhhhhhhhhh %@",[matches valueForKey:@"credentails"]);

    NSMutableSet *query = [matches mutableSetValueForKey:@"credentails"];


    NSArray *financialData =[matches valueForKeyPath:@"credentails"];
    NSLog(@"%@",financialData);
    NSLog(@"%@",[financialData valueForKey:@"date"]);

的数据是核心数据内但是我不知道它正在执行的关系，食物实体被填充，并且也填充CredentialsFood

我也收到了警告抽象实体食物没有孩子抽象实体凭据没有子节点抽象实体CredentialsFood没有孩子

提前致谢

Answer 1

首次创建对象时：

CredentialsFood *credentialsFood = (CredentialsFood *) [NSEntityDescription insertNewObjectForEntityForName:@"CredentialsFood" inManagedObjectContext:context1];
NSDate *currentDate = [NSDate date];
credentialsFood.toFood.food_id = item_id;
credentialsFood.toCred.email = @"123";

...您似乎没有为toFood或toCred关系分配任何内容。相关对象不是自动创建的，因此这些属性将为零。在Objective-C中，当这些属性为nil时，运行此代码并不是错误，但代码无效。看起来您需要创建（或获取）Food和Credentials的实例，并将这些新对象分配给toFood和toCred属性。

核心数据关系，如何从关系中插入和检索数据

1 个答案: