说我们有一个实体Company ,通过employenes 与employee 实体有多种关系。
如果我想找到最后一个创建的 Employee (assume Employenee 有 NSDate 属性 created ), 这两种方法中哪一种更好?
NSFetchRequest on Employee, restricted to "company == %@", someCompany, sort by created, and set the fetchLimit to 1sortedArrayUsingDescriptors: on someCompany.employees with a NSSortDescriptor on created and take the first?第二种方法似乎更加直截了当,但我对实际处理方式感到担心。 第一种方法允许系统定制自定义查询,而第二种方法则进行一些模拟排序。 我猜它归结为许多关系是否懒惰。
根据我个人的经验,我将采取第一种办法。
首先,您不需要像第二步那样执行两步操作。 此外,您还可以对元素拥有完全控制( 您将抓取限制设定为 1 ) 。 您可以在抓取请求时抓取( 例如, 您可以指定要检索的属性, 使用 < code> setPropertysToFetch , 并授权 Core Data 来为您打开错误) 。
然后,当你做 someCompany.employenes 时,你取回了为数不多的有缺陷的物体(例如20个),它们虽然在记忆中,但却在记忆中,它们占据着它。当你应用了某种描述符(可能在此时会向他们开枪)时,你最终会发现19个在记忆中,但对于应用寿命周期没有用处的物体。
<强度 > 个人注释
即使我是一个好的程序员,我相信核心数据框架优化,我会采取第一种方式。
希望能帮上忙
Core Data uses lazy loading for this type of relationship. Thus, the first approach seems to be better. But I recommend filling your database with a lot of records and testing both of them. You may also want to read Core Data Performance section.
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