HQL：通过查询（包括JOIN）只从实体检索几个字段

Question

我有以下Hibernate表：

public class Customer {
    //some fields... include customerId field
    public Person person;
    @OneToOne(cascade = { CascadeType.ALL },  fetch = FetchType.LAZY)
    @JoinColumn(name = "person_id", unique = false, nullable = true, insertable = true, updatable = true)
    public Person getPerson e () {
        return person;
    }

}

 public class Person {
    //some fields...

    private Set<History> histories;

    @ManyToMany(fetch=FetchType.LAZY, targetEntity=History.class,cascade={CascadeType.PERSIST,CascadeType.MERGE})
    @JoinTable(name="person_m2m_history",joinColumns={@JoinColumn(name="person_id")},
            inverseJoinColumns={@JoinColumn(name="persone_history_id")})
    public Set<History> getHistories() {
        return this.histories;
    }       
}

entityManager.createQuery("select c.customerId, ph.changedOn,
    ph.changedField, from Customer c 
    left join fetch c.person p 
    left join fetch p.histories ph 
    where ph.changedField = 'name'")

这是Createquery导致的错误：

'org.hibernate.queryException：查询指定了联接提取，但提取的关联的所有者不在选择列表中[fromelement{explicit,not a collection join、fetch join、fetch non-lazy properties,classalias=e,role=myproject.Customer.person,tablename=person,tablealias=person,tablename=person,tablealias=person1_,origin=customer0_,columns={customer0_.person_id,

Answer 1

检查您的查询，它在from、from附近有一个额外的逗号

entityManager.createQuery("select c.customerId, ph.changedOn,
    ph.changedField from Customer c 
    left join fetch c.person p 
    left join fetch p.histories ph 
    where ph.changedField = 'name'")

可能有用。