Question

如何创建一个试图在数组内的字典中查找对象的NSPredicate？

例如：

MyArray {
[0]: Dictionary {
               email: test@test.com
               name: John Smith
               }
[1]: Dictionary {
               email: other@test.com
               name: Mary Davis
               }

}

如何在“名称”字段中查看MyArray是否包含“Mary Davis”？

我试过

NSString *user = @"Mary Davis";
NSString *criteria = [NSString stringWithFormat:@"name == '%@'", user];
NSPredicate *filter = [NSPredicate predicateWithFormat:criteria];
NSArray *results = [collaborators  filteredArrayUsingPredicate:filter];

和

NSString *user = @"Mary Davis";
NSString *criteria = [NSString stringWithFormat:@"name MATCHES[cd] '%@'", user];
NSPredicate *filter = [NSPredicate predicateWithFormat:criteria];
NSArray *results = [collaborators  filteredArrayUsingPredicate:filter];

和

NSString *user = @"Mary Davis";
NSString *criteria = [NSString stringWithFormat:@"object MATCHES[cd] '%@'", user]; 
NSPredicate *filter = [NSPredicate predicateWithFormat:criteria];
NSArray *results = [collaborators  filteredArrayUsingPredicate:filter];

但似乎都没有用。我知道我能做到

for (int i=0; i (less than) myArray.count; i++){
    NSDictionary *dict = [myArray objectAtIndex:i];
    if ([[dict objectForKey:@"name"] isEqualToString:user])
        return ;
}

它有效，但我需要这个作为谓词，因为我试图使用PFQuery queryWithClassName谓词从Parse.com获取数据。

是否有可能做到这一点，或者相信一个谓词会神奇地横穿阵列是没有希望的？

Answer 1

好的，找到了另一个解决方案......

NSPredicate* predicate = [NSPredicate predicateWithFormat:@"name contains[cd] %@", user];

有效，但根据PFQuery文档，Parse不支持“contains”：

The following types of predicates are supported:
* Simple comparisons such as =, !=, , =, and BETWEEN with a key and a constant.
* Containment predicates, such as “x IN {1, 2, 3}”.
* Key-existence predicates, such as “x IN SELF”.
* BEGINSWITH expressions.
* Compound predicates with AND, OR, and NOT.
* SubQueries with “key IN %@”, subquery.

The following types of predicates are NOT supported:
* Aggregate operations, such as ANY, SOME, ALL, or NONE.
* Regular expressions, such as LIKE, MATCHES, CONTAINS, or ENDSWITH.
* Predicates comparing one key to another.
* Complex predicates with many ORed clauses.

有什么建议吗？

Answer 2

显然，Parse需要对此类问题采取不同的看法，如此处所述http://blog.parse.com/2013/03/19/implementing-scalable-search-on-a-nosql-backend/

因此，在我的情况下，正确的方法是创建另一个表Collaborator，其中包含“name”和“email”字段，并在原始表中保留对此表的引用数组。

然而，由于我已经实现了大量代码，我做了一个解决方法 - 在同一个表上创建了一个附加数组列，只包含我想要的用户名信息。通过这种方式，我能够进行查询

NSPredicate *predicate = [NSPredicate predicateWithFormat:@"name IN {%@}", user];
        query = [PFQuery queryWithClassName:table predicate:predicate];

希望这有助于某人！ :-D

干杯！

NSPredicate - 在NSArray中查找NSDictionary内的对象

2 个答案: