使用 NSPredicate 获取 Core Data 对象数组？

发布于 2024-10-03 12:53:53 字数 349 浏览 7 评论 0原文

假设我有一个名为 Person 的核心数据实体。我如何获得属性与某些值匹配的人员的 NSArray？例如，具有特定年龄、身高或体重的人...或者具有特定值的身高、体重和年龄的人...

我可以像这样使用 NSPredicate 吗：

NSPredicate *pred = 
[NSPredicate predicateWithFormat:
@"(age == 25) OR (height_in_cms == 185) OR (age == 30 AND height_in_cms == 170 AND weight_in_kgs == 80)"; 
// All properties are NSNumber

原文

Say I have a Core Data entity called Person. How would I get an NSArray of Persons whose properties match certain values? For instance someone of a particular age, height, or weight... or someone with a whose height,weight and age are specific values...

Can I use an NSPredicate like so:

NSPredicate *pred = 
[NSPredicate predicateWithFormat:
@"(age == 25) OR (height_in_cms == 185) OR (age == 30 AND height_in_cms == 170 AND weight_in_kgs == 80)"; 
// All properties are NSNumber

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時窥 2024-10-10 12:53:53

我不是 predicateWithFormat: 语法方面的专家，但您已经了解了基本要点。您可以在 Apple 的 Predicate 中找到有关格式的详细信息编程指南。如果您询问拥有谓词后如何处理该谓词，这里有一个片段向您展示了步骤：

// Create a fetch request.
NSFetchRequest *fetchRequest = [[NSFetchRequest alloc] init];

// Set the entity for the fetch request.
NSEntityDescription *entity = [NSEntityDescription entityForName:@"EntityName" inManagedObjectContext:managedObjectContext];
[fetchRequest setEntity:entity];
[entity release];

// Set the predicate for the fetch request.
[fetchRequest setPredicate:predicate];

// Perform the fetch.
NSError *error;
NSArray *array = [managedObjectContext executeFetchRequest:fetchRequest error:&error];
[fetchRequest release];

如果您希望对结果进行排序，您可以使用 setSortDescriptors: 在执行获取之前。

I'm not an expert on the syntax for predicateWithFormat:, but you have the basic gist. You can find details on the format in Apple's Predicate Programming Guide. If you're asking what to do with the predicate once you have it, here is a snippet that shows you the steps:

// Create a fetch request.
NSFetchRequest *fetchRequest = [[NSFetchRequest alloc] init];

// Set the entity for the fetch request.
NSEntityDescription *entity = [NSEntityDescription entityForName:@"EntityName" inManagedObjectContext:managedObjectContext];
[fetchRequest setEntity:entity];
[entity release];

// Set the predicate for the fetch request.
[fetchRequest setPredicate:predicate];

// Perform the fetch.
NSError *error;
NSArray *array = [managedObjectContext executeFetchRequest:fetchRequest error:&error];
[fetchRequest release];

If you want the results to be sorted, you can pass an array of sort descriptors to the fetch request using setSortDescriptors: prior to executing the fetch.

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