问题描述
我有这个问题，我想不出如何写这个谓词.
I have this problem where I can't think of how to write this predicate.
我有一个名为 Contact 的实体，它有一个字符串属性pages"，比方说
I have an Entity called Contact, it has a string property "pages", let's say
contact.pages = @"1,5,11,15,17";
我的数据库中有很多联系人，我只想获取这些包含特定 ID 的联系人.所以假设我只想获取这些联系人，哪些页面包含 id @"1".
There is a lot of contacts in my database, and I want to fetch only these contacts that contains a certain id. So let's say I want to fetch only these contacts, which pages contains id @"1".
我能想到这样的事情，
NSPredicate* predicate = [NSPredicate predicateWithFormat:@"self.pages CONTAINS %@", _pageId];
但我的问题是这也会得到联系人，例如具有 pages = @"11,15".
But my problem is that this would also get contacts, that e.g has pages = @"11,15".
那么关于如何实现这一目标的任何想法?如有任何建议，我将不胜感激，提前致谢！
So any ideas on how to achieve that?I would be grateful for any suggestions, thanks in advance!
推荐答案
NSPredicate 的MATCHES"运算符可用于与正则表达式进行比较:
The "MATCHES" operator of NSPredicate can be used to compare against a regular expression:
NSString *pageId = @"1";
NSString *regex = [NSString stringWithFormat:@"(.*,)?%@(,.*)?", pageId];
NSPredicate *predicate = [NSPredicate predicateWithFormat:@"pages MATCHES %@", regex];
但是您还应该考虑将字符串属性替换为与 Page 实体的一对多关系，那么谓词将看起来像
But you should also consider to replace the string property by a to-many relationship to a Page entity, then the predicate would look like
NSPredicate *predicate = [NSPredicate predicateWithFormat:@"ANY pages.pageid == %@", pageId];
这篇关于从包含 id 的字符串形成 NSPredicate的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持！