SUBQUERY在NSPredicate和NSInvalidArgumentException

问题描述

我在Core Data中设置了以下模型。

  Book有一个to-many关系，称为toBookOrders，实体。反向称为toBook。 
 Book有一个BOOL值属性叫isSync。 
  

我设置了以下 NSPredicate / p>

  NSEntityDescription * entityDescription = [NSEntityDescription entityForName：@BookinManagedObjectContext：moc]; 
 NSPredicate * predicate = [NSPredicate predicateWithFormat：@isSync == 0 AND SUBQUERY（toBookOrders，$ x，$ x.toBook == SELF）]; 
  

通过这个谓词，我只需要抓取尚未同步的书籍及其相关订单。 / p>

这是我收到的错误。

任何想法？

解决方案

这是您的问题的症结：

  @ isSync == 0 AND SUBQUERY（toBookOrders，$ x，$ x.toBook == SELF）
  

如果你把它拆分成两个subpredicates，如Scott建议，你会得到：

• isSync == 0


• SUBQUERY（toBookOrders，$ x，$ x.toBook = = SELF）

问题是每个 SUBQUERY 不返回true或false，因为谓词必须。它返回一个集合（一个数组），一个数组不是真或假的相同的东西。因此，在创建谓词时，您会收到一个错误，表示它是无效的格式，因为 AND 后的东西不是谓词。

您可能

：

  @isSync == 0 AND SUBQUERY（toBookOrders，$ x，$ x.toBook == SELF）@ count> 0
  

这将给你一个谓词，以找到 isSync 为false的所有书，并且至少一个书 OrderBooks 是书。

I set up the following model in Core Data.

Book has a to-many relationship, called toBookOrders, with OrderBook entity. The inverse is called toBook.
Book has a BOOL value property called isSync.

I set up the following NSPredicate.

NSEntityDescription* entityDescription = [NSEntityDescription entityForName:@"Book" inManagedObjectContext:moc];
NSPredicate* predicate = [NSPredicate predicateWithFormat:@"isSync == 0 AND SUBQUERY(toBookOrders, $x, $x.toBook == SELF)"];

Through this predicate I need to grab only books that haven't been synchronized and theirs relative orders.

This is the error I receive.

Any ideas? Thank you in advance.

解决方案

Here's the crux of your problem:

@"isSync == 0 AND SUBQUERY(toBookOrders, $x, $x.toBook == SELF)"

If you split that up into the two subpredicates, as Scott suggests, you'll get:

• isSync == 0
• SUBQUERY(toBookOrders, $x, $x.toBook == SELF)

The problem is that every SUBQUERY does not return true or false, as a predicate must. It returns a collection (an array), and an array is not the same thing as true or false. Thus, when you create the predicate, you're getting an error that it's an invalid format, because the stuff after the AND isn't a predicate. It's simply an expression.

You're probably wanting:

@"isSync == 0 AND SUBQUERY(toBookOrders, $x, $x.toBook == SELF).@count > 0"

This would give you a predicate to find all the books where isSync is false and the at least one of the Book's OrderBooks is that Book.

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