如何使用LEFT JOIN创建JPA NamedQuery

Question

我有两个实体：Car（汽车）和Reservation（预订）。我想使用LEFT JOIN创建一个命名查询。我尝试按照这里描述的方式执行此操作 How to create JPA query with LEFT OUTER JOIN，但是它并没有起作用。您有任何想法吗？我的查询有什么问题吗？我想显示具有NULL预订的汽车。无论如何，即使使用JOIN也不起作用。在启动应用程序后，我遇到了一个错误：

Caused by: org.hibernate.HibernateException: Errors in named queries: Car.findAll
    at org.hibernate.internal.SessionFactoryImpl.<init>(SessionFactoryImpl.java:495) ~[hibernate-core-5.0.12.Final.jar:5.0.12.Final]
    at org.hibernate.boot.internal.SessionFactoryBuilderImpl.build(SessionFactoryBuilderImpl.java:444) ~[hibernate-core-5.0.12.Final.jar:5.0.12.Final]
    at org.hibernate.jpa.boot.internal.EntityManagerFactoryBuilderImpl.build(EntityManagerFactoryBuilderImpl.java:879) ~[hibernate-entitymanager-5.0.12.Final.jar:5.0.12.Final]
    ... 22 common frames omitted

原则上，我想要实现这个在MySQL中有效的查询

SELECT distinct * FROM car c LEFT JOIN reservation r ON c.id = r.car_id WHERE c.producer='producer' AND c.model='model' AND c.type='type' 
AND (r.date_of_rent < 'date1' AND r.date_of_return < 'date1') OR (r.date_of_rent > 'date2') OR r.date_of_rent IS NULL;

汽车实体

import java.io.Serializable;
import java.util.List;

import javax.persistence.Entity;
import javax.persistence.GeneratedValue;
import javax.persistence.GenerationType;
import javax.persistence.Id;
import javax.persistence.NamedQuery;
import javax.persistence.OneToMany;

@Entity
@NamedQuery(name = "Car.findAll", query = "SELECT c FROM Car c LEFT JOIN c.reservation r WHERE c.producer=:producer "
        + "AND c.type=:type AND c.dailyPrice=:dailyPrice")
public class Car implements Serializable {
    private static final long serialVersionUID = 1L;

    @Id
    @GeneratedValue(strategy = GenerationType.IDENTITY)
    private Long id;
    private String producer;
    private String model;
    private int seatsNumber;
    private String type;
    private String registrationNumber;
    private double dailyPrice;
    private String description;
    @OneToMany(mappedBy = "car")
    private List<Reservation> reservations;

预订实体

import java.io.Serializable;
import java.sql.Date;

import javax.persistence.Entity;
import javax.persistence.GeneratedValue;
import javax.persistence.GenerationType;
import javax.persistence.Id;
import javax.persistence.ManyToOne;

@Entity
public class Reservation implements Serializable {
    private static final long serialVersionUID = 1L;

    @Id
    @GeneratedValue(strategy = GenerationType.IDENTITY)
    private Long id;
    @ManyToOne
    private User user;
    @ManyToOne
    private Car car;
    private Date dateOfRent;
    private Date dateOfReturn;

感谢您的帮助。 更新 问题已解决。查询应该像这样。

import java.io.Serializable;
import java.util.List;

import javax.persistence.Entity;
import javax.persistence.GeneratedValue;
import javax.persistence.GenerationType;
import javax.persistence.Id;
import javax.persistence.NamedQuery;
import javax.persistence.OneToMany;

@Entity
@NamedQuery(name = "Car.findAll", query = "SELECT DISTINCT c FROM Car c LEFT JOIN c.reservations r WHERE "
        + "c.type=:type AND c.dailyPrice<=:dailyPrice AND ((r.dateOfRent < :dateOfRent AND r.dateOfReturn < :dateOfRent) OR "
        + "(r.dateOfRent > :dateOfReturn) OR (r.dateOfRent IS NULL))")
public class Car implements Serializable {
    private static final long serialVersionUID = 1L;

    @Id
    @GeneratedValue(strategy = GenerationType.IDENTITY)
    private Long id;
    private String producer;
    private String model;
    private Integer seatsNumber;
    private String type;
    private String registrationNumber;
    private Double dailyPrice;
    private String description;
    @OneToMany(mappedBy = "car")
    private List<Reservation> reservations;

- bartoszsokolik

---

请在问题中添加：为什么需要左连接？ - v.ladynev

“它不起作用”？这是什么意思？你得到了一个异常吗？它运行了一些 SQL（你没有发布），但你得到了与预期不同的结果？还是根本什么都没发生？ - Neil Stockton

我发布了一个带错误的查询，我想实现哪个查询。 - bartoszsokolik

@bartekms274 最好添加包含错误描述的堆栈跟踪部分。"Errors in named queries: Car.findAll"并没有提供很多信息。我已经在我的答案中更新了该错误。 - v.ladynev

Answer 1

SELECT c FROM Car c LEFT JOIN c.reservation r WHERE c.producer=:producer "
        + "AND c.type=:type AND c.dailyPrice=:dailyPrice

这个查询中有一个错误，c.reservation需要改成c.reservations。

我想展示那些有NULL预定的汽车。

你不能用这种方法做。尝试从以下查询开始：

select c from Car c where not exists (
    select r.id from Reservation r where r.car.id = c.id
)

- v.ladynev