xcode 如何在Core Data中选择特定数据？
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How to select specific data in Core Data?
提问by kimbebot
I have a sample program that use Core Data and load an sqlite database in it. And I am displaying all the values using this code
我有一个使用 Core Data 并在其中加载 sqlite 数据库的示例程序。我正在使用此代码显示所有值
NSFetchRequest *fetchRequest = [[NSFetchRequest alloc] init];
NSEntityDescription *entity = [NSEntityDescription entityForName:@"Name"
inManagedObjectContext:context];
[fetchRequest setEntity:entity];
NSArray *fetchedObjects = [context executeFetchRequest:fetchRequest error:&error];
for (Name *name in fetchedObjects) {
NSLog(@"ID: %@", name.nameId);
NSLog(@"First Name: %@", name.first);
NSLog(@"Middle Name: %@", name.middle);
NSLog(@"Last Name: %@", name.last);
}
This code works fine, my problem here is that I can't select a specific data/record. Example I want to select the record with the ID = 1.
这段代码工作正常，我的问题是我无法选择特定的数据/记录。示例 我想选择 ID = 1 的记录。
Thanks!
谢谢！
回答by Pierre
You have to use predicates (with NSPredicate) before your request execution.
您必须在请求执行之前使用谓词（使用 NSPredicate）。
Something like that :
类似的东西：
NSPredicate *predicateID = [NSPredicate predicateWithFormat:@"nameID == %d",-1];
[fetchRequest setPredicate:predicateID];
回答by Janak Nirmal
NSFetchRequest *fetchRequest = [[NSFetchRequest alloc] init];
NSEntityDescription *entity = [NSEntityDescription entityForName:@"Name"
inManagedObjectContext:context];
[fetchRequest setEntity:entity];
//Add following method to your code. this will help you to get desired result.
[fetchRequest setPredicate:[NSPredicate predicateWithFormat:@"yourColumnID == %@", yourID]];
NSArray *fetchedObjects = [context executeFetchRequest:fetchRequest error:&error];
for (Name *name in fetchedObjects) {
NSLog(@"ID: %@", name.nameId);
NSLog(@"First Name: %@", name.first);
NSLog(@"Middle Name: %@", name.middle);
NSLog(@"Last Name: %@", name.last);
}
