如何使用 LEFT JOIN 创建 JPA NamedQuery

Question

我有两个实体：汽车和预订。 我想用 LEFT JOIN 创建命名查询。 我试图像这里描述的那样做这件事How to create JPA query with LEFT OUTER JOIN但它不起作用。 你知道我的查询有什么问题吗？ 我想展示保留为 NULL 的汽车。 无论如何，即使使用 JOIN 它也不起作用。 启动应用程序后，我有一个错误：

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;

非常感谢您的帮助。

更新

问题解决了。 查询应如下所示

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;

Answer 1

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

此查询有错误c.reservation需要更改为c.reservations 。

我想展示保留为 NULL 的汽车。

你不能这样做。 尝试从这个查询开始：

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