Hibernate - HQL从单向OneToMany关系获取集合 [英] Hibernate - HQL to fetch a collection from Unidirectional OneToMany relationship

问题描述

  public class Order {
 @ OneToMany（cascade = CascadeType.ALL）
 @JoinTable（name =order_item，joinColumns = {@ JoinColumn（name =order_id）}，inverseJoinColumns = {@ JoinColumn（name =item_id）}）
 public Set< Item> getItems（）{
返回项目; 
 
 
  

正常情况下，获取此订单的内容很简单：

 列表<项目> items = order.getItems（）; 
  

但是无论出于何种原因，我可能想要以某种方式过滤我的结果并仅检索部分集合的项目，如所有的项目超过一定的价格，低于某些股票等尽可能最快的方式（不返回，然后所有，然后过滤）。要做到这一点，我会运行一个HQL查询来检索特定订单的商品，并在我的where子句或我的查询对象中添加更多的东西。

直觉上我会想要这样的行为（这是完全错误的）：

pre $ 从join_tablem中选择jointable.ITEM作为jointable inner join jointable.order where order = ：订单


但当然这是错误的，因为HQL根据映射实体工作，所以我不能使用查询中的连接表。那么做到这一点的正确方法是什么？

编辑：

我已经找到了这个问题的答案，我想要以下查询：

 从Order o中选择o.items其中o =？ 
  

这使我可以获取订单项目的集合，而无需使用双向关系。我现在对这个问题的第二个阶段感到困惑，那就是如何过滤这个集合的结果，最简单的例子是：

 从Order o中选择o.items，其中o =？ order by o.items.someumberfield asc 
  

哪个返回非法尝试解引用集合，那么如何过滤我的物品？
$ b

编辑：

票证解决方案实际上是正确的，

解决方案

 从订单中选择商品
内部连接order.items item 
 where order =：order 
 and ... 
  

HQL查询使用实体及其关联。关联使用连接表的事实对于HQL并不重要：您可以通过关联进行导航，Hibernate会对SQL进行相应的转换。

I have an Class with a unidirectional one to many relationship as follows:

public class Order {
    @OneToMany(cascade = CascadeType.ALL)
    @JoinTable(name="order_item", joinColumns={@JoinColumn(name="order_id")}, inverseJoinColumns={@JoinColumn(name="item_id")})
    public Set<Item> getItems() {
        return items;
    }
} 

Normally getting the contents of this order is straightforward:

List<Item> items = order.getItems();

But for whatever reason I might want to filter my results in some way and retrieve only part of a collection of items such as all items more than a certain price, below a certain stock etc in the fastest way possible (Not returning then all then filtering afterwards). To do this I would run a HQL query to retrieve the items for a particular order and add some more stuff into my where clause or onto my query object.

Intuitively I would want this behaviour (Which is completely wrong):

SELECT jointable.ITEM from order_item as jointable inner join jointable.order where order = :order

But of course this is wrong as HQL works in terms of mapped entities, so I cannot use the join table in the query. So what is the correct way to do this?

Edit:

I have found the answer to this question, I want the following Query:

Select o.items from Order o where o = ?

This allows me to fetch the collection of items for an order, without having to use a bidirectional relationship. I am now however confused on the second stage of this question, which is how to filter the results of this collection, the most simple example being:

Select o.items from Order o where o = ? order by o.items.somenumberfield asc

Which returns illegal attempt to dereference collection, so how would I filter my items?

Edit:

The ticket solution is actually correct, I misread the solution originally.

解决方案

select item from Order order
inner join order.items item
where order = :order
and ...

HQL queries use entities and their associations. The fact that the association uses a join table or not is not important for HQL: you navigate through associations and Hibernate does the appropriate translation to SQL.

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