核心数据对多关系。它们是延迟负载吗？ [英] Core Data to-many relationships. Are they Lazy Load?

问题描述

我有一个典型的模型在核心数据（iPhone）与部门和雇员（部门 - >>员工）。

我不想加载所有员工一个部门，每次我加载它，所以我想我会创建Employee作为获取属性。我想我可以这样定义一些谓词：

  employee.deparmentId = department.departmentId 
  
 
 
 
但我不能（使用Xcode图形编辑器）。
 
 
 
 
 
 
 
我的问题是：是多对多关系Lazy正在加载？或者每次我创建（检索）部门列表时，是否会在数据库中加载我的所有员工？
 
 
 
感谢提前
 Gonso 
解决方案
否，与多对和一对一关系相关的对象默认是长时间加载的。但是，如果您需要在每次获取部门时访问其中许多部门，那么出于性能原因，您可能会要求Core Data同时加载它们（这称为预取）。您可以执行以下操作：
  [fetchRequest setReturnsObjectsAsFaults：NO]; 
 [fetchRequest setRelationshipKeyPathsForPrefetching：[NSArray arrayWithObjects：@employees，nil]]; 
  
 
I have the typical model in Core Data (for iPhone) with Departments and Employesss (Department ->> Employee).

I dont want to load all employees of a department each time I load it, so I thought I'd create the Employee as a Fetched Property. I thought I could define some Predicate like this:
employee.deparmentId = department.departmentId
but I couldn't (with Xcode graphic editor).

Now, reading some posts, Im inclined to define a relationship to-many for Department to Employee (and its reverse) and use it.

My question is: Are to-many relationship Lazy Loading? or is it going to load all my Employees in the "database" each time I create (retrieve) a list of departments?

Thanks in advance
Gonso
解决方案
No, objects related to to-many and to-one relationships are loaded lazily by default. However, If you need to access many of them each time you fetch a Department, then for performance reasons you may ask Core Data to load them simultaneously (this is called pre-fetching). You can do this as follow:
[fetchRequest setReturnsObjectsAsFaults:NO];
[fetchRequest setRelationshipKeyPathsForPrefetching:[NSArray arrayWithObjects:@"employees", nil]];


                        
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