NSPredicate，获得具有一对多关系子集的结果 [英] NSPredicate, get results with a subset of one-to-many relationship

问题描述

我正在使用Core Data和 NSFetchedResultsController 。

我的数据模型如下所示：

产品与一对多的关系称为 dataLines 。
dataLine 实体具有属性名 theWeek 。

我要获取所有产品，其中 dataLines.theWeek == someValue 。这很容易用子查询完成。但这返回所有的dataLines。是否可以创建返回 Product 的 NSPredicate 和一个子集，如果dataLines只与 dataLines == someValue ？

解决方案

使用SUBQUERY

  [NSPredicate predicateWithFormat：@SUBQUERY dataLines，$ x，$ x.theWeek ==％@）。@ count> 0），[NSNumber numberWithInt：18]]; 
  

或ANY修饰符

  [NSPredicate predicateWithFormat：@ANY dataLines.theWeek ==％@，[NSNumber numberWithInt：18]]; 
  

如果您需要检查多个值，您还可以执行以下操作：

  [NSPredicate predicateWithFormat：@SUBQUERY（dataLines，$ x，$ x.theWeek ==％@或$ x.theWeek ==％@）。 @count> 0），[NSNumber numberWithInt：18]，[NSNumber numberWithInt：19]]; 
  

同样适用于 ANY 。 任何...或任何... 。

也许如果你分享一些代码，我们可以帮助你。 / p>

PS我想你不使用标量值和 theWeek 是一个数字。

希望它有帮助。 >

I'mm working around with Core Data and NSFetchedResultsController.

My Data Model looks like this:

Product with one-to-many relationship called dataLines. The dataLine entity has a property name theWeek.

I want to fetch all Product where dataLines.theWeek == someValue. This is easily done with a subquery. But this returns all dataLines. Is it possible to create a NSPredicate that returns the Product and a subset if dataLines only with the dataLines == someValue?

解决方案

What you want to achieve could be reached in two ways:

using a SUBQUERY

[NSPredicate predicateWithFormat:@"SUBQUERY(dataLines, $x, $x.theWeek == %@).@count > 0)", [NSNumber numberWithInt:18]];

or the ANY modifier

[NSPredicate predicateWithFormat:@"ANY dataLines.theWeek == %@", [NSNumber numberWithInt:18]];

You can do also the following if you need to check against multiple values:

[NSPredicate predicateWithFormat:@"SUBQUERY(dataLines, $x, $x.theWeek == %@ or $x.theWeek == %@).@count > 0)", [NSNumber numberWithInt:18], [NSNumber numberWithInt:19]];

The same can be applied to ANY modifier. ANY ... OR ANY ....

Maybe if you share some code we could help you.

P.S. I suppose you don't use scalar values and theWeek is a number.

Hope it helps.

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