我如何使用@OneToMany集合进行分页 [英] How can I do paging with @OneToMany collections
问题描述
假设我有一个Post实体和一个Comment实体以及一对多的关系:
pre $ @ $ c $ @Entity class Post {
...
@OneToMany
List< Comment>注释;
...
}
如何实现这样的分页:
发帖= //找到帖子。
返回post.getComments()。fetch(100,10); //找到第11页(页面大小10);
是否可以使用@OneToMany集合在JPA,
或我们是否必须完全重写JPA的关联机制? (例如,创建一个可以管理分页,排序和搜索的PersistentList集合类型)。
P.S .:我最近发现了Play!框架在JPA之上使用了一个非常有趣的lib:Siena。 Siena非常易于使用,并且在JPA / Hibernate之上是一个很好的抽象。但我无法找到如何对其关联进行分页。
更新:
Play框架有一个查询类似于Django的语法:
Post.findAll()。from(100).fetch(10); //分页
其中
Post.findAll()
将返回一个JPAQuery对象,一个自定义查询键入Play。
但与关联的集合,例如:
Post.comments
只会返回一个List,它不支持分页或其他查询。
Post.comments
也会返回一个JPAQuery对象或类似对象,那么你可以在query集合上查询:
Post.comments.from(100).fetch(10);
或者插入一个新的评论,而不会实际提取任何评论:
Post.comments.add(新评论(...));
我的第一个想法是,我们可以创建List的子类,然后Post类变为:
@Entity class Post {
...
@OneToMany
QueryList< Comment>注释;
...
}
和QueryList将具有fetch(),from ()方法,这对JPAQuery是间接的。
但我不知道Hibernate / JPA是否会识别它,或干扰它。
是否有可能在JPA(...) $ b之上使用@OneToMany集合来模拟动态分页? $ b
不支持。标准方法是使用JPQL查询来检索给定帖子的注释,并使用 Query#setFirstResult(int)
和 Query# setMaxResults(int)
。
在我第一次想到的时候,我们可以创建一个List的子类, )。但是我不知道Hibernate / JPA是否会识别它,或者干扰它。
显然,如果没有 heavy 修补程序彻底改变默认行为。
Suppose I have a Post entity and a Comment entity and a one to many relationship:
@Entity class Post {
...
@OneToMany
List<Comment> comments;
...
}
How can I achieve paging like this:
Post post = //Find the post.
return post.getComments().fetch(100, 10); // Find the 11th page (page size 10);
Is it possible to emulate dynamic paging with @OneToMany collections on top of JPA, or do we have to rewrite the association mechanism of JPA totally ? (e.g. create a PersistentList collection type that could manage the paging, sorting and searching).
P.S.: I recently found the Play! framework uses a very interesting lib on top of JPA: Siena. Siena is very easy to use, and is a good abstraction on top of JPA/Hibernate. But I can't find how to do paging with its associations.
Update:
Play framework has a query syntax similar to Django:
Post.findAll().from(100).fetch(10); // paging
where
Post.findAll()
will return a JPAQuery object, a customized query type in Play.
But with associated collections, e.g.:
Post.comments
will just return a List, which doesn't support paging or other queries.
I was wondering how to extend it, so that
Post.comments
will also return a JPAQuery object or similar, then you can query on the "query" collection:
Post.comments.from(100).fetch(10);
or insert a new Comment without actually fetching any of the comments:
Post.comments.add(new Comment(...));
On my first thought, we could create a subclass of List, then the Post class would become:
@Entity class Post {
...
@OneToMany
QueryList<Comment> comments;
...
}
and QueryList will have fetch(), from() methods that indirect to JPAQuery's.
But I don't know whether Hibernate/JPA will recognize this, or interfere with it.
Is it possible to emulate dynamic paging with @OneToMany collections on top of JPA (...)
Not supported. The standard approach would be to use a JPQL query to retrieve the comments for a given post and and to use Query#setFirstResult(int)
and Query#setMaxResults(int)
.
On my first thought, we could create a subclass of List, (...). But I don't know whether Hibernate/JPA will recognize this, or interfere with it.
It obviously won't without an heavy patch to drastically change the default behavior.
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