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实际查询：-

SELECT *,COUNT(case when ZISREAD = 0 then ZISREAD end) FROM ZNOTIFICATION WHERE ZTTL>1411025900  group by zkind,zaction,zname

嗨，我需要COUNT(case when ZISREAD = 0 then ZISREAD end)使用核心数据转换计数条件NSExpression 

 NSExpression *countPathExpression = [NSExpression expressionForKeyPath: @"isRead"];

 NSExpression *countExpression = [NSExpression expressionForFunction: @"count:"
                                                              arguments: [NSArray arrayWithObject:countPathExpression]];

    NSExpressionDescription *countExpressionDescription = [[NSExpressionDescription alloc] init];
    [countExpressionDescription setName: @"count"];
    [countExpressionDescription setExpression: countExpression];
    [countExpressionDescription setExpressionResultType: NSInteger32AttributeType];

COUNT(case when ZISREAD = 0 then ZISREAD end)我需要帮助人们转换NSExpression

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1 回答 1

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首先，您可以在 fetch 请求中添加一个谓词：

fetchRequest.predicate = [NSPredicate predicateWithFormat:@"isRead = NO"];

然后你想在要获取的属性中指定你的表达式：

fetchRequest.propertiesToFetch = @[countExpression];

不要忘记设置结果类型

fetchRequest.resultType = NSDictionaryResultType;

那应该让你继续前进。请记住，如果要跨属性评估表达式，还可以使用 propertiesToGroupBy 数组，例如按天分组，这将允许您查看每天的计数：)

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于 2014-09-23T17:20:07.330 回答