加载实体ManyToMany Assotiation的JPA，Spring，Hibernate问题

Question

我正在尝试从关联N：N获取数据，但收到空白字段。
有我的Hibernate映射类：

@Entity
@Table(name = "companies")
public class Company extends NamedEntity {
 //some_code

@ManyToMany(
        targetEntity = com.hqcargo.shippingstock.domain.CompanyProfile.class,
        cascade = {CascadeType.ALL, CascadeType.ALL },
        fetch = FetchType.EAGER
        )
@JoinTable(
        name = "company_company_profiles",
        joinColumns = {@JoinColumn(
                        name = "company_id",
                        referencedColumnName = "id") },
        inverseJoinColumns = {@JoinColumn(
                        name = "company_profile_id",
                        referencedColumnName = "id") }
        )
private List<CompanyProfile> profiles;
// getters and setters + other code

其他班：

@Entity
@Table(name = "company_profiles")
public class CompanyProfile extends NamedEntity {
//some_code
@ManyToMany(
        targetEntity = com.hqcargo.shippingstock.domain.Company.class,
        cascade = {CascadeType.ALL, CascadeType.ALL }, 
        mappedBy = "profiles",
        fetch = FetchType.EAGER
        )
@JoinTable(
        name = "company_company_profiles",
        joinColumns = {@JoinColumn(
                        name = "company_profile_id",
                        referencedColumnName = "id") },
        inverseJoinColumns = {@JoinColumn(
                        name = "company_id",
                        referencedColumnName = "id") }
        )
 private List<Company> companies;
 // getters and setters + other code

此类适用于保存，但不适用于加载数据。
下面我添加DAO类：

public class CompanyJpaDAO extends JpaDaoSupport
implements CompanyDAO {

@Transactional(readOnly = true)
public Company readById(Long id) {
    Company tempCompany = getJpaTemplate().find(Company.class, id);
    return tempCompany;
    }
}

@Transactional
public void update(Company existingInstance) {
    if (existingInstance.isNew()) {
        throw new InvalidDataAccessApiUsageException(
            "Can't update record. Given instance don't have assigned ID");
    }
    save(existingInstance);
}

当我更新一切正常（由Hibernate生成sql）时：

251252 [13627369@qtp-8132032-9] DEBUG org.hibernate.SQL  -
update
    companies
set
    name=?,
where
    id=?
Hibernate:
update
    companies
set
    name=?,
where
    id=?
251295 [13627369@qtp-8132032-9] DEBUG org.hibernate.SQL  -
insert
into
    company_company_profiles
    (company_id, company_profile_id)
values
    (?, ?)
Hibernate:
insert
into
    company_company_profiles
    (company_id, company_profile_id)
values
    (?, ?)

但是当我加载数据时，我没有从company_company_profiles（Hibernate生成的SQL）中获取信息

36088 [13507994@qtp-8132032-13] DEBUG org.hibernate.SQL  -
select
    companies0_.company_profile_id as company2_8_,
    companies0_.company_id as company1_8_,
    company1_.id as id3_0_,
    company1_.name as name3_0_,
from
    company_company_profiles companies0_
left outer join
    companies company1_
        on companies0_.company_id=company1_.id
where
    companies0_.company_profile_id=?
Hibernate:
select
    companies0_.company_profile_id as company2_8_,
    companies0_.company_id as company1_8_,
    company1_.id as id3_0_,
    company1_.name as name3_0_,
from
    company_company_profiles companies0_
left outer join
    companies company1_
        on companies0_.company_id=company1_.id
where
    companies0_.company_profile_id=?

您在我的代码中看到任何错误吗？

Answer 1

我不确定这是问题的原因，但是您不应该在多对多关联的两侧指定JoinTable 。 根据JPA规范， JoinTable批注位于关联的所属方（在您的情况下为Company ）：

9.1.25 JoinTable注释

JoinTable批注用于关联映射。 JoinTable批注是在多对多关联的拥有方或单向一对多关联中指定的。

因此，请在CompanyProfile实体中将其删除：

@Entity
@Table(name = "company_profiles")
public class CompanyProfile extends NamedEntity {
    //some_code
    @ManyToMany(
        targetEntity = com.hqcargo.shippingstock.domain.Company.class,
        cascade = {CascadeType.ALL, CascadeType.ALL }, 
        mappedBy = "profiles",
        fetch = FetchType.EAGER
    )
    private List<Company> companies;
    // getters and setters + other code
}

然后再试一次。

参考文献

• JPA 1.0规范
  • 第2.1.8.4节“双向多对多关系”
  • 第9.1.25节“ JoinTable注释”
  • 第9.1.26节“多对多注释”