如何对Entity-Bean @OneToMany关系应用默认限制 [英] How to apply a default-restriction on Entity-Bean @OneToMany Relationships

问题描述

我有两个实体模型，客户模型和订单模型.每个客户可能有数千个订单.这两个实体之间存在OneToMany和ManyToOne关系.

I have two entity models, Customer and Order. Each customer could have thousands of orders. I have a OneToMany and ManyToOne relationship between these two entities.

如何将这种关系的列表限制为仅排名前10位的订单?

How do I restrict this relationship's list to only top 10 orders?

是否可以将"WHERE"条件用作@OneToMany上的属性?

Is it possible to apply 'WHERE' condition as an attribute on @OneToMany or not?

赞:

@OneToMany("Where Order.orderNo > 100")

我的问题是，当由实体管理器创建的对象的所有订单都在内存中创建时. 延迟加载无法解决问题，因为我需要在默认结构中获得前十名的订单.

My problem is when the object created by Entity Manager all Orders are created in memory. Lazy loading can not solve my consideration, because I need to get top 10 orders in default construction.

推荐答案

我的意思是说是否可以将'WHERE'条件用作@OneToMany上的属性?

I mean if it is possible to apply 'WHERE' condition as an attribute on @OneToMany or not?

不适用于标准JPA.但是某些提供商对此进行了扩展.例如，Hibernate确实具有@Where批注:

Not with standard JPA. But some providers have extensions for this. For example, Hibernate does have a @Where annotation:

@OneToMany(cascade=CascadeType.ALL, fetch=FetchType.EAGER)
@Where(clause="1=1")
public Set<Ticket> getTickets() {
    return tickets;
}

参考文献

• 休眠注释参考指南
  • 2.4.6.集合相关的注释

  References

  • Hibernate Annotations Reference Guide
    • 2.4.6. Collection related annotations

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