java - 多对多查询 jpql

Question

我有以下麻烦。

有一个实体 Distributor 与实体城镇的多对多关系相关联：

@Entity
public class Distributor{

   @ManyToMany
   @JoinTable( name = "GS_DISTRIBUTOR_TOWN",
           joinColumns = @JoinColumn(name = "CD_DISTRIBUTOR"),
           inverseJoinColumns = @JoinColumn(name = "CD_TOWN") )
   private List<Town> towns;

   ....
}

那么实体镇也和District有关系

@Entity
public class Town{

   @ManyToMany(mappedBy="towns")
   private List<Distributor> distributors;

   @ManyToOne
   private District district;

   ....
}

现在我必须过滤（使用 jpql）在一个地区的所有经销商。我能怎么做？

Answer 1

select distinct distributor 
from Distributor distributor  
join distributor.towns town 
join town.district district 
where district.name = :name

请参阅：https ://en.wikibooks.org/wiki/Java_Persistence/JPQL

Answer 2

首先，从实体 Town 来看，@Manytoone 的关系映射不正确。应该：

@Entity
public class District {

  .....

   @ManyToOne
   private Town town;

   ....
}