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我有一个核心数据实体无法解决的问题。

在我的实体中，有两个关系（whoHasToPay、whoHasToBePaid）和一个属性（howMuch）。

这是我在数据库中插入记录的代码

Debitcredit *dc = [NSEntityDescription
  insertNewObjectForEntityForName:@"Debitcredit"
  inManagedObjectContext:self.context];
dc.howMuch = [NSNumber numberWithFloat:5.2f];
dc.whoHasToPay = theDebitor;
dc.whoHasToBePaid = theCreditor;
NSLog(@"%@", dc);
[self.context save:&error];

NSLog 显示

<Debitcredit: 0x151590> (entity: Debitcredit; id: 0x141570 
  <x-coredata:///Debitcredit/t8DC4691F-5DE3-42D5-8095-C2D5D3264C8D2> ; data: {
  howMuch = "5.2";
  whoHasToBePaid = "0x140c50 <x-coredata://C25DC4FE-B46B-402C-B513-A2A83C6A9F86/Users/p1>";
  whoHasToPay = "0x14c280 <x-coredata://C25DC4FE-B46B-402C-B513-A2A83C6A9F86/Users/p2>";
})

所以这个值howMuch似乎是正确的。

但是，当我再次调用它时

fetchRequestCount = [[NSFetchRequest alloc] init];
entityCount = [NSEntityDescription entityForName:@"Debitcredit"      
  inManagedObjectContext:self.context];
[fetchRequestCount setEntity:entityCount];
fetchedObjectsCount = [self.context executeFetchRequest:fetchRequestCount error:&error];
for (Debitcredit *dc in fetchedObjectsCount) {
    NSLog(@"%f", [dc valueForKey:@"howMuch"]);
    NSLog(@"%@", [[dc valueForKey:@"whoHasToPay"] name]);
    NSLog(@"%@", [[dc valueForKey:@"whoHasToBePaid"] name]);
}
[fetchRequestCount release];

NSLog 显示

2010-12-05 01:47:04.636 myApp[6179:307] 0.000000
2010-12-05 01:47:04.642 myApp[6179:307] John
2010-12-05 01:47:04.646 myApp[6179:307] Jack

好像howMuch已经归零了。为什么？我错了吗？

4

1 回答 1

3

这是一个日志记录错误。浮点数和其他数值存储为 NSNumber 对象。这个：

[dc valueForKey:@"howMuch"]

...返回一个 NSNumber 对象，而不是一个浮点值。您需要将日志更改为：

NSLog(@"%@", [dc valueForKey:@"howMuch"]);

...您应该看到正确的值。

于 2010-12-05T01:02:27.077 回答