ios - 你如何构造 NSFetchRequest setHavingPredicate :? 的谓词

Question

对于我的生活，我似乎无法让它发挥作用。

假设我们的实体是一个具有状态字段和订单字段的托管对象。

我将如何获得所有具有多个相同订单的 orderedEntries？

请不要回答告诉我只在主谓词中使用@count 进行子查询，因为我知道那个解决方案，这篇文章的重点是了解如何在核心数据中使用 having 谓词，这反正可能比子查询更快。 (除非你解释为什么我不能使用 having 子句)

以下代码将返回一个字典数组，其中包含每个订单号的订单数。我想要的是能够添加一个 having 子句来限制我的请求只返回代表那些计数大于 1 的订单对象的字典。

这是到目前为止的代码以及我对 having 谓词的尝试:

NSFetchRequest *fetchRequest = [[NSFetchRequest alloc] init];
NSEntityDescription *entity = [NSEntityDescription entityForName:@"OrderedEntry"
                                          inManagedObjectContext:context];
[fetchRequest setEntity:entity];
[fetchRequest setResultType:NSDictionaryResultType];

NSPredicate *predicate = [NSPredicate predicateWithFormat:
                 @"(status == %@)",[NSNumber numberWithInt:EntryStatusAlive]];


[fetchRequest setPredicate:predicate];


NSExpression *keyPathExpression = [NSExpression expressionForKeyPath: @"order"]; // Does not really matter
NSExpression *maxExpression = [NSExpression expressionForFunction: @"count:"
                                                        arguments: [NSArray arrayWithObject:keyPathExpression]];
NSExpressionDescription *expressionDescription = [[NSExpressionDescription alloc] init];
[expressionDescription setName: @"orderCount"];
[expressionDescription setExpression: maxExpression]; 
[expressionDescription setExpressionResultType: NSInteger32AttributeType];

[fetchRequest setPropertiesToFetch: [NSArray arrayWithObjects:expressionDescription,@"order",nil]];


[fetchRequest setPropertiesToGroupBy:[NSArray arrayWithObjects:@"order",nil]];
//[fetchRequest setHavingPredicate:[NSPredicate predicateWithFormat:@"@count > 1"]];
//[fetchRequest setHavingPredicate:[NSComparisonPredicate predicateWithLeftExpression:maxExpression rightExpression:[NSExpression expressionForConstantValue:[NSNumber numberWithInteger:1]] modifier:NSDirectPredicateModifier type:NSGreaterThanPredicateOperatorType options:NSCaseInsensitivePredicateOption]];

NSError *error;

NSArray * array = [context executeFetchRequest:fetchRequest error:&error];

Answer 1

我最终为任何感兴趣的人选择了这个

-(BOOL)ordersAreSaneOnDay:(NSNumber*)dayNumber forUser:(User*)user inContext:(NSManagedObjectContext*)context {
NSFetchRequest *fetchRequest = [[NSFetchRequest alloc] init];
NSEntityDescription *entity = [NSEntityDescription entityForName:@"BasicEntry"
                                          inManagedObjectContext:context];
[fetchRequest setEntity:entity];
[fetchRequest setResultType:NSDictionaryResultType];

NSPredicate *predicate = [NSPredicate predicateWithFormat:
                 @"(status == %@) && ((type != %@) && (type != %@) && (dayNumber == %@))  && ((user == NIL) || (user == %@))",[NSNumber numberWithInt:EntryStatusAlive],[NSNumber numberWithInt:EntryTypeTask],[NSNumber numberWithInt:EntryTypeCompletedTask],dayNumber,user];


[fetchRequest setPredicate:predicate];


NSExpression *keyPathExpression = [NSExpression expressionForKeyPath: @"order"]; // Does not really matter
NSExpression *maxExpression = [NSExpression expressionForFunction: @"count:"
                                                        arguments: [NSArray arrayWithObject:keyPathExpression]];
NSExpressionDescription *expressionDescription = [[NSExpressionDescription alloc] init];
[expressionDescription setName: @"orderCount"];
[expressionDescription setExpression: maxExpression]; 
[expressionDescription setExpressionResultType: NSInteger32AttributeType];

[fetchRequest setPropertiesToFetch: [NSArray arrayWithObjects:expressionDescription,@"order",nil]];
[expressionDescription release];

[fetchRequest setPropertiesToGroupBy:[NSArray arrayWithObjects:@"order",nil]];
//[fetchRequest setHavingPredicate:[NSPredicate predicateWithFormat:@"self.order.@count > 1"]];
//[fetchRequest setHavingPredicate:[NSComparisonPredicate predicateWithLeftExpression:maxExpression rightExpression:[NSExpression expressionForConstantValue:[NSNumber numberWithInteger:1]] modifier:NSDirectPredicateModifier type:NSGreaterThanPredicateOperatorType options:NSCaseInsensitivePredicateOption]];

NSError *error;

NSArray * array = [context executeFetchRequest:fetchRequest error:&error];
array = [array filteredArrayUsingPredicate:[NSPredicate predicateWithFormat:@"orderCount > 1"]];
//NSLog(@"it worked %@",array);
[fetchRequest release];

if ([array count]) return FALSE;
return TRUE;