java多人查询jpql

Question

我遇到了麻烦

有一家实体分销商与实体小镇的众多关系有关：

@Entity
public class Distributor{

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

   ....
}

那么实体城镇也与地区有关

@Entity
public class Town{

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

   @ManyToOne
   private District district;

   ....
}

现在，我必须（用jpql）过滤一个地区的所有分销商。 我该怎么办

Answer 1

首先，从实体城镇来看，@Manytoone的关系映射不正确。 应该是：

@Entity
public class District {

  .....

   @ManyToOne
   private Town town;

   ....
}

Answer 2

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

见：https://en.wikibooks.org/wiki/Java_Persistence/JPQL