急切地加载一个懒惰的子集合 [英] Eager loading a lazy child collection

问题描述

我有类似于此的数据模型

  class Office 
 {
 @ManyToOne 
 @JoinColumn（name =cafeteria_id）
自助餐厅自助餐厅; 
} 
 
 class Cafeteria 
 {
 @OneToMany（mappedBy =cafeteria）
 @LazyCollection（value = LazyCollectionOption.EXTRA）
列表与LT椅子>椅子; 
} 
 
类椅子
 {
 @ManyToOne 
 @JoinColumn（name =cafeteria_id）
自助餐厅自助餐厅; 
} 
  

我有这样的JPQL查询

 从办公室o选择o o.cafeteria.someThing =？ 
  

上面的查询可以正常工作，但在一种情况下，我希望能够加载所有椅子的查询o.cafeteria.chairs）。我应该如何修改查询以热切地获取所有椅子？使用 fetch 使用解决方案>属性在 OneToMany 注释中。您可以根据需要多次映射相同的关系：



  class Cafeteria {
 @OneToMany（mappedBy =食堂）
 @LazyCollection（value = LazyCollectionOption.EXTRA）
 List< Chair>椅子; 
 
 @OneToMany（fetch = FetchType.EAGER，mappedBy =cafeteria）
 List< Chair> eagerlyLoadedChairs; 
} 
  

然后您可以使用它们中的任何一个：

  //延迟加载
从Office中选择o内部加入o.cafeteria c内部加入c.chairs ch其中c.someThing =？ 
 
 // Eager加载
从Office中选择o内部加入o.cafeteria c内部加入c.eagerlyLoadedChairsch其中c.someThing =？ 
  




I have data model similar to this

class Office
{
   @ManyToOne
   @JoinColumn(name = "cafeteria_id")
   Cafeteria cafeteria;
}

class Cafeteria
{
   @OneToMany(mappedBy="cafeteria")
   @LazyCollection(value=LazyCollectionOption.EXTRA)
   List<Chair> chairs;
}

class Chair
{
    @ManyToOne
    @JoinColumn(name = "cafeteria_id")
    Cafeteria cafeteria;
}

I have a JPQL query like this

select o from Office o where o.cafeteria.someThing = ?

Above query works fine but in one case I would like a query which could eagerly load all the chairs(o.cafeteria.chairs) as well. How should I modify query to eagerly fetch all chairs?

解决方案

Use fetch attribute in OneToMany annotation. You can map the same relationship as many times as you want:

class Cafeteria {
   @OneToMany(mappedBy="cafeteria")
   @LazyCollection(value=LazyCollectionOption.EXTRA)
   List<Chair> chairs;

   @OneToMany(fetch = FetchType.EAGER, mappedBy="cafeteria")
   List<Chair> eagerlyLoadedChairs;
}

And then you can use any of them:

// Lazy loading
select o from Office o inner join o.cafeteria c inner join c.chairs ch where c.someThing = ?

// Eager loading
select o from Office o inner join o.cafeteria c inner join c.eagerlyLoadedChairsch where c.someThing = ?

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