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假设我有 2 个实体， aPerson和 a Transaction。

PersonTransaction与和具有一对多关系Transaction实体具有amount和date。我的目标是NSFetchRequest基于Person，但我只想知道在特定日期和SUM交易金额之间进行交易的人。

我的代码如下所示：

NSExpression *amountKeyPath = [NSExpression expressionForKeyPath:@"transactions.amount"];
NSExpression *sumAmountExpression = [NSExpression expressionForFunction:@"sum:" arguments:@[amountKeyPath]];

// Create the expression description for that expression.
NSExpressionDescription *description = [[NSExpressionDescription alloc] init];
[description setName:@"sum"];
[description setExpression:sumAmountExpression];
[description setExpressionResultType:NSDecimalAttributeType];

// Create the sum amount fetch request,
self.sumAmountFetchRequest = [NSFetchRequest fetchRequestWithEntityName:@"Person"];
self.sumAmountFetchRequest.resultType = NSDictionaryResultType;
self.sumAmountFetchRequest.predicate = [NSPredicate predicateWithFormat:@"SUBQUERY(transactions, $t, $t.date >= %@ AND $t.date <= %@).@count > 0", self.startDate, self.endDate];
self.sumAmountFetchRequest.propertiesToFetch = @[@"name", description];

一切似乎都很好，但是......当我查看生成的 SQL 查询时，它看起来像：

SELECT t0.ZPERSONID, t0.ZNAME, 
    (SELECT TOTAL(t2.ZAMOUNT) FROM ZTRANSACTION t2 WHERE (t0.Z_PK = t2.ZPERSON) ) 
FROM ZPERSON t0 
WHERE (SELECT COUNT(t1.Z_PK) FROM ZTRANSACTION t1 WHERE (t0.Z_PK = t1.ZPERSON AND (( t1.ZDATE >= ? AND  t1.ZDATE <= ?))) ) > ?

所以，似乎NSExpression声明的，不尊重NSPredicatefetchRequest 创建的。

是否有可能使表达式也尊重附加到 fetchRequest 的谓词？或者既然NSExpression独立存在，我应该附加另一个谓词？

4

1 回答 1

5

我没有任何东西可以支持我自己的答案，但是在为此苦苦挣扎了几个小时之后。我认为这不是NSExpression不尊重 fetchRequest NSPredicate，而是更多地是 fetchRequest 的谓词是子查询。

SELECT t0.ZPERSONID, t0.ZNAME, 
    (SELECT TOTAL(t2.ZAMOUNT) FROM ZTRANSACTION t2 WHERE (t0.Z_PK = t2.ZPERSON) ) 
FROM ZPERSON t0 
WHERE 
     (SELECT COUNT(t1.Z_PK) FROM ZTRANSACTION t1 WHERE (t0.Z_PK = t1.ZPERSON AND (( t1.ZDATE >= ? AND  t1.ZDATE <= ?))) ) > ?

所以，谓词中的子查询并没有真正转换成WHERE我想要的子句。我认为如果它正在创建一个JOIN，那就行了。

我最终的解决方案是反其道而行之。如果我从中创建 fetchRequest Transaction，那就完美了。

NSExpression *amountKeyPath = [NSExpression expressionForKeyPath:@"amount"];
NSExpression *sumAmountExpression = [NSExpression expressionForFunction:@"sum:" arguments:@[amountKeyPath]];

// Create the expression description for that expression.
NSExpressionDescription *description = [[NSExpressionDescription alloc] init];
[description setName:@"sum"];
[description setExpression:sumAmountExpression];
[description setExpressionResultType:NSDecimalAttributeType];

// Create the sum amount fetch request,
self.sumAmountFetchRequest = [NSFetchRequest fetchRequestWithEntityName:@"Transaction"];
self.sumAmountFetchRequest.resultType = NSDictionaryResultType;
self.sumAmountFetchRequest.predicate = [NSPredicate predicateWithFormat:@"date >= %@ AND date <= %@", self.startDate, self.endDate];
self.sumAmountFetchRequest.propertiesToFetch = @[@"person.name", description];
self.sumAmountFetchRequest.propertiesToGroupBy = @[@"person.name"];

这完美无缺。它必须按 the 分组，"person.name"以便根据需要使用sum:。

生成的 SQL 将是

SELECT  t1.ZPERSONID, total( t0.ZAMOUNT) 
FROM ZTRANSACTION t0 
      LEFT OUTER JOIN ZPERSON t1 ON t0.ZPERSON = t1.Z_PK 
WHERE ( t0.ZDATE >= ? AND  t0.ZDATE <= ?) GROUP BY  t1.ZPERSONID

干杯，

于 2013-07-11T14:17:41.717 回答