Realm Cocoa：通过 PK 查找多个对象

Question

潜伏已久，第一次提问。

我在一个项目中使用 Realm Cocoa（来自 Realm.io）并且正在努力通过 PK 执行搜索。假设我有一个名为 RLMFoo 的实体，它有一个名为 bar 的主键。我还有一个 PK 列表，假设存储在一个数组中：

NSArray *primaryKeys = @[@"bar1", @"bar2", @"bar3"]

有没有办法在一次查询中从我的领域检索 class RLMFoo 的所有实体？

到目前为止我已经尝试过：

谓词格式：[RLMFoo objectsInRealm:realm withPredicate:[NSPredicate predicateWithFormat:@"bar IN %@", primaryKeys]];
领域所在：[RLMFoo objectsInRealm:realm where:@"bar IN %@", strippedIds];
带块的谓词：

.

NSPredicate *predicate = [NSPredicate predicateWithBlock:^BOOL(id
evaluatedObject, NSDictionary *bindings) {
                    RLMFoo *foo = (RLMFoo *)evaluatedObject;
                    return [primaryKeys containsObject:foo.bar];
                }];
        [RLMFoo objectsInRealm:realm withPredicate:predicate];

但到目前为止，我发现唯一可行的方法是查询领域中的每个主键值并聚合结果，这看起来很慢：

NSMutableArray *results = [NSMutableArray new];
for (NSString *primaryKey in primaryKeys) {
    RLMFoo *obj = [RLMFoo objectInRealm:realm forPrimaryKey:primaryKey];
    if (obj) {
        [results addObject:obj];
    }
}

有谁知道更好的方法吗？

=========解释为什么前三种方法不起作用=======

1) 从异常消息中可以看出这不起作用的原因：IN 仅采用 2 个值，尽管 IN 的 SQL 版本应采用尽可能多的值。我们从RLMQueryUtil.mm的源码可以看出，同样适用于BETWEEN运算符：

        if (compp.predicateOperatorType == NSBetweenPredicateOperatorType || compp.predicateOperatorType == NSInPredicateOperatorType) {
        // Inserting an array via %@ gives NSConstantValueExpressionType, but
        // including it directly gives NSAggregateExpressionType
        if (exp1Type != NSKeyPathExpressionType || (exp2Type != NSAggregateExpressionType && exp2Type != NSConstantValueExpressionType)) {
            @throw RLMPredicateException(@"Invalid predicate",
                                         @"Predicate with %s operator must compare a KeyPath with an aggregate with two values",
                                         compp.predicateOperatorType == NSBetweenPredicateOperatorType ? "BETWEEN" : "IN");
        }

这是堆栈跟踪：

*** Terminating app due to uncaught exception 'Invalid predicate', reason: 'Predicate with IN operator must compare a KeyPath with an aggregate with two values'
*** First throw call stack:
(
    0   CoreFoundation      0x03334946 __exceptionPreprocess + 182
    1   libobjc.A.dylib     0x0292aa97 objc_exception_throw + 44
    2   <redacted>          0x00190569 _ZN12_GLOBAL__N_127update_query_with_predicateEP11NSPredicateP9RLMSchemaP15RLMObjectSchemaRN7tightdb5QueryE + 2553
    3   <redacted>          0x0018f7ea _Z27RLMUpdateQueryWithPredicatePN7tightdb5QueryEP11NSPredicateP9RLMSchemaP15RLMObjectSchema + 378
    4   <redacted>          0x0018b23c _Z13RLMGetObjectsP8RLMRealmP8NSStringP11NSPredicate + 748
    5   <redacted>          0x0017d721 +[RLMObject objectsInRealm:withPredicate:] + 161

2) 这在原因和堆栈跟踪上非常相似：

*** Terminating app due to uncaught exception 'Invalid predicate', reason: 'Predicate with IN operator must compare a KeyPath with an aggregate with two values'
*** First throw call stack:
(
    0   CoreFoundation      0x03328946 __exceptionPreprocess + 182
    1   libobjc.A.dylib     0x0291ea97 objc_exception_throw + 44
    2   <redacted>          0x00184599 _ZN12_GLOBAL__N_127update_query_with_predicateEP11NSPredicateP9RLMSchemaP15RLMObjectSchemaRN7tightdb5QueryE + 2553
    3   <redacted>          0x0018381a _Z27RLMUpdateQueryWithPredicatePN7tightdb5QueryEP11NSPredicateP9RLMSchemaP15RLMObjectSchema + 378
    4   <redacted>          0x0017f26c _Z13RLMGetObjectsP8RLMRealmP8NSStringP11NSPredicate + 748
    5   <redacted>          0x00171751 +[RLMObject objectsInRealm:withPredicate:] + 161
    6   <redacted>          0x00171465 +[RLMObject objectsInRealm:where:args:] + 213
    7   <redacted>          0x001712f3 +[RLMObject objectsInRealm:where:] + 419

3) 这个也非常相似。归根结底是领域缺乏对 NSPredicate 完整功能集的支持。

*** Terminating app due to uncaught exception 'Invalid predicate', reason: 'Only support compound and comparison predicates'
*** First throw call stack:
(
    0   CoreFoundation      0x03308946 __exceptionPreprocess + 182
    1   libobjc.A.dylib     0x028fea97 objc_exception_throw + 44
    2   <redacted>          0x001638bd _ZN12_GLOBAL__N_127update_query_with_predicateEP11NSPredicateP9RLMSchemaP15RLMObjectSchemaRN7tightdb5QueryE + 4397
    3   <redacted>          0x0016240a _Z27RLMUpdateQueryWithPredicatePN7tightdb5QueryEP11NSPredicateP9RLMSchemaP15RLMObjectSchema + 378
    4   <redacted>          0x0015de5c _Z13RLMGetObjectsP8RLMRealmP8NSStringP11NSPredicate + 748
    5   <redacted>          0x00150341 +[RLMObject objectsInRealm:withPredicate:] + 161

Answer 1

您的前两个选项应该没问题。编写此查询的最简单方法是：

NSArray *primaryKeys = @[@"bar1", @"bar2", @"bar3"]
RLMResults *results = [RLMFoo objectsWhere:@"id IN %@", primaryKeys];

一个叫做 objectsWithPredicate 的方法也可以。您可以分享更多使用前几种方法时的 code/stack 轨迹吗？我认为其他地方发生了问题

Answer 2

在您的帮助下，我找到了这种行为的原因。我的真实代码更接近于：

  NSArray *primaryKeys = @[ @"bar1", @"bar2", @"bar3" ];

  NSString *primaryKeyName = @"bar";
  RLMResults *results =
      [RLMFoo objectsInRealm:self.realm
               withPredicate:[NSPredicate predicateWithFormat:@"%@ IN %@",
                                                              primaryKeyName,
                                                              primaryKeys]];

在方法中，PK 和 PK 名称是方法调用的参数。理论上，这将允许我的 class 检索具有任何 PK 名称的任何对象。原来我的错误是假设 predicateWithFormat 在这种情况下会以与 stringWithFormat 类似的方式工作，并正确地将 PK 名称替换为第一个参数，并将 PK 数组作为第二个参数。然而解决方案原来是首先组装格式字符串，然后是谓词：

  RLMResults *results = [RLMFoo
      objectsInRealm:self.realm
       withPredicate:[NSPredicate
                         predicateWithFormat:
                             [NSString stringWithFormat:@"%@ IN %%@", primaryKeyName],
                             primaryKeys]];

感谢 Yoshyosh 抽出时间。

Realm Cocoa：通过 PK 查找多个对象

Realm Cocoa: finding multiple objects by PKs

objective-c

realm

ios