Question

假设我有2个实体，Person和Transaction。

Person与Transaction和Transaction实体之间存在多对多关系amount和date。我的目标是根据NSFetchRequest获得Person，但我只想知道在特定日期和交易金额SUM之间进行交易的人。

我的代码如下：

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 <= ?))) ) > ?

因此，似乎NSExpression声明了，并不尊重fetchRequest创建的NSPredicate。

是否可以使表达式也遵循附加到fetchRequest的谓词？或者由于NSExpression独立，我应该附加另一个谓词吗？

Answer 1

我没有任何东西支持我自己的答案，但经过几个小时的挣扎。我认为不是NSExpression不尊重fetchRequest的NSPredicate，而是更多的是fetchRequest的谓词是子查询这一事实。

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 <= ?))) ) > ?

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

我的解决方案最终是以相反的方式工作。如果我从Transaction创建fetchRequest，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"];

完美无缺。必须按"person.name"对其进行分组，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，

NSExpression尊重子查询NSPredicate

1 个答案: