子查询 IN 语句集合

Question

NSArray *sectionNames = [NSArray arrayWithObjects: @"aa", @"bb", nil];

RLMResults<Department *> *filteredDepartments = [Department objectsWhere:
                                            [NSString stringWithFormat:@"SUBQUERY(sections, $section,  $section.name IN %@).@count > 0",[NSArray arrayWithArray:sectionNames]]]; 

这是部门模型。

@interface Department : RLMObject

@property NSString *name;

@property (nonatomic, strong) RLMArray<Section> *sections;

@end 

我有这个错误。 sectionNames 是 section 对象的名称数组。

*** Terminating app due to uncaught exception 'NSInvalidArgumentException', reason: 'Unable to parse the format string "SUBQUERY(sections, $section,  $section.name IN (
)).@count > 0"'

Answer 1

您应该使用NSPredicate 的参数替换支持，而不是通过+[NSString stringWithFormat:] 使用NSString 的字符串插值：

NSPredicate *predicate = [NSPredicate predicateWithFormat:@"SUBQUERY(sections, $section, $section.name IN %@).@count > 0", sectionNames];
RLMResults<Department *> *filteredDepartments = [Department objectsWithPredicate:predicate];

由于这是一种常见的模式，Realm 提供了一个包装器，负责为您构建NSPredicate，格式为+[RLMObject objectsWhere:]：

RLMResults<Department *> *filteredDepartments = [Department objectsWhere:@"SUBQUERY(sections, $section, $section.name IN %@).@count > 0", sectionNames];

NSString 的插值将变量的字符串表示形式插入到字符串中。数组的字符串表示形式为(aa, bb)，即not valid in an NSPredicate format string。使用 NSPredicate 的参数替换将 object 替换到谓词中，而无需担心字符串表示是否与 NSPredicate 期望的匹配。