Grails - OpenSessionInView does not work with SiteMesh

最新推荐文章于 2017-08-09 16:17:23 发布

robinfung

最新推荐文章于 2017-08-09 16:17:23 发布

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文章标签： Grails

本文链接：https://blog.youkuaiyun.com/robinfung/article/details/83556185

本文介绍Grails框架中如何配置关联关系的抓取策略（急切或懒加载）。默认情况下，Grails采用懒加载方式，但在某些场景下使用急切加载可以避免N+1查询问题。文章通过示例说明如何为一对多关联配置急切加载。

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grails 's bug description:

http://jira.codehaus.org/browse/GRAILS-2764

fetchMode

Purpose

Allows the configuration of an associations fetch strategy ('eager' or 'lazy')

Examples

class Author {
   String name
   static hasMany = [books:Book]
   static fetchMode = [books:'eager']
}

In this example the fetchMode static property specifies that the book association should be fetching eagerly

Description

By default associations in Grails are fetched lazily (each record is read from the database only when its first accessed from the collection). This makes sense for most cases, however in the case where you have a small number of records to fetch and/or are repeatedly required to load lazy associations (resulting in N+1) it makes sense to use eager fetching.

In the case of eager fetching and a one-to-many association, the instance as well as the association will be initialized when they are loaded (eagerly). However, caution should be observed when using eager fetching, being too eager can result in your entire database being loaded into memory!