是否可以仅提取Core Data查询中的选定属性 [英] Is it possible to fetch only selected property in a Core Data query

问题描述

我有（我猜）典型的问题。我的核心数据数据库包含表，它们有BLOB字段和相当长的文本字段。

I have (I guess) typical problem. My Core Data database contains table, which have BLOB fields and quite long text fields.

通常我不需要加载这些大字段。由于在数据库中有几千条记录，我更喜欢只获取我真正需要的数据。换句话说，我想要SELECT name，id FROM TAB_NAME查询，而不是SELECT * FROM TAB_NAME查询。

Usually I do not need to load agrresivly those large size fields. Since there are several thousand records in a database I would prefer to fetch only data I truly need. In other words I would like to make "SELECT name, id FROM TAB_NAME" query, not "SELECT * FROM TAB_NAME" query.

有任何方法，字段使用Core Data？或者我应该寻找一些其他选项，例如，将大字段分隔到另一个表？也许有更好的（更简单）的方法来做到这一点？

Is there any way to fetch only selected fields using Core Data? Or shall I look for some other option, like, for instance, seperate large fields to another table? Maybe there is a better (easier) way to do this?

我习惯于使用Hibernate或JPA，它很容易做上述操作，核心数据文档我没有看到这样的选项。

I am used to working with Hibernate or JPA, where it easy to do described above operation, after going through Core Data docs I do not see such option.

推荐答案

换句话说， SELECT name，id FROM TAB_NAMEquery，notSELECT * FROM TAB_NAMEquery。

In other words I would like to make "SELECT name, id FROM TAB_NAME" query, not "SELECT * FROM TAB_NAME" query.

此问题的答案已被接受，但FYI，这里是如何获取一个实体的特定属性与Core Data，而不重新考虑你的模型：

The answer to this question was accepted, but FYI, here's how to fetch only specific properties of an entity with Core Data, without re-factoring your model:

// build your NSFetchRequest
// ...

[request setResultType:NSDictionaryResultType];
[request setPropertiesToFetch:
  [NSArray arrayWithObjects:@"property1", @"property2", /* etc. */ nil]];    

另请参阅NSFetchRequest 。

这篇关于是否可以仅提取Core Data查询中的选定属性的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持IT屋！