Hibernate 6 JPA JDK 11 Apache Netbeans 12 Maven 中的 Hql 查询

Question

当我执行如下查询（1）时：

  private EntityManagerFactory emf;
    private EntityManager em;

emf=Persistence.createEntityManagerFactory("hibernate");
         em=emf.createEntityManager();
 Query query = em.createQuery("SELECT COUNT(*) FROM Album");
Long resul=  (long) query.getSingleResult();
System.out.println("Media de precios:" +  resul);

在这里，我的实体是：

package Modelo;

import java.io.Serializable;
import java.util.Objects;
import javax.persistence.Column;
import javax.persistence.Entity;
import javax.persistence.GeneratedValue;
import javax.persistence.GenerationType;
import javax.persistence.Id;
import javax.persistence.Table;

/**
 *
 * @author javier
 */
@Entity
@Table (name="album") 
public class Album implements Serializable {

    private static final long serialVersionUID = 1L;
    
    @Id
      @Column(name="numalbum")
    private int id;
    
    
     @Column(name="titulo")
    private String titulo;
     @Column(name="autor")
    private String autor;
    
     @Column(name="precio")
    private int precio;
     

    public Album() {
    }

    public Album(String titulo, String autor) {
        this.titulo = titulo;
        this.autor = autor;
    }

    public Album(int id, String titulo, String autor, int precio) {
        this.id = id;
        this.titulo = titulo;
        this.autor = autor;
        this.precio = precio;
    }

    public int getId() {
        return id;
    }

    public void setId(int id) {
        this.id = id;
    }

    public String getTitulo() {
        return titulo;
    }

    public void setTitulo(String titulo) {
        this.titulo = titulo;
    }

    public String getAutor() {
        return autor;
    }

    public void setAutor(String autor) {
        this.autor = autor;
    }

    public int getPrecio() {
        return precio;
    }

    public void setPrecio(int precio) {
        this.precio = precio;
    }

    @Override
    public int hashCode() {
        int hash = 5;
        hash = 67 * hash + this.id;
        hash = 67 * hash + Objects.hashCode(this.titulo);
        hash = 67 * hash + Objects.hashCode(this.autor);
        hash = 67 * hash + this.precio;
        return hash;
    }

    @Override
    public boolean equals(Object obj) {
        if (this == obj) {
            return true;
        }
        if (obj == null) {
            return false;
        }
        if (getClass() != obj.getClass()) {
            return false;
        }
        final Album other = (Album) obj;
        if (this.id != other.id) {
            return false;
        }
        if (this.precio != other.precio) {
            return false;
        }
        if (!Objects.equals(this.titulo, other.titulo)) {
            return false;
        }
        if (!Objects.equals(this.autor, other.autor)) {
            return false;
        }
        return true;
    }

    @Override
    public String toString() {
        return "Album{" + "id=" + id + ", titulo=" + titulo + ", autor=" + autor + ", precio=" + precio + '}';
    }

sql：

CREATE DATABASE IF NOT EXISTS `musica` DEFAULT CHARACTER SET utf8mb4 COLLATE utf8mb4_general_ci;
USE `musica`;

-- --------------------------------------------------------

--
-- Estructura de tabla para la tabla `album`
--

CREATE TABLE `album` (
  `numalbum` int(11) NOT NULL,
  `titulo` varchar(30) NOT NULL,
  `autor` varchar(30) DEFAULT NULL,
  `precio` int(11) DEFAULT NULL
) ENGINE=InnoDB DEFAULT CHARSET=utf8mb4 COLLATE=utf8mb4_general_ci;

--
-- Volcado de datos para la tabla `album`
--

INSERT INTO `album` (`numalbum`, `titulo`, `autor`, `precio`) VALUES
(8, 'motomami', 'rosalia', 80),
(20, 'bailar', 'sergio', 120);

持久化单元：

<?xml version="1.0" encoding="UTF-8"?>
<persistence xmlns="http://xmlns.jcp.org/xml/ns/persistence"
             xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
             xsi:schemaLocation="http://xmlns.jcp.org/xml/ns/persistence
             http://xmlns.jcp.org/xml/ns/persistence/persistence_2_1.xsd"
             version="2.1">
    
   <persistence-unit name="hibernate" transaction-type="RESOURCE_LOCAL">
    <provider>org.hibernate.jpa.HibernatePersistenceProvider</provider>
        <properties>
      <property name="javax.persistence.jdbc.url" value="jdbc:mysql://localhost:3306/musica"/>
      <property name="javax.persistence.jdbc.user" value="root"/>
      <property name="javax.persistence.jdbc.password" value=""/>
      <property name="javax.persistence.jdbc.driver" value="com.mysql.cj.jdbc.Driver"/>
      <property name="hibernate.show_sql" value="true"/>
      <property name="hibernate.dialect" value="org.hibernate.dialect.MySQLDialect"/>
    </properties>
  </persistence-unit>
</persistence>

当我执行代码（1）时，Apache Netbeans 12 的输出给出以下错误：

simpleorg.hibernate.query.sqm.InterpretationException：解释查询时出错 [SELECT COUNT(*) FROM Album]；这可能表明语义（用户查询）问题或解析器中的错误

我不知道如何解决这个错误，所以我查看了hibernate 6.0手册。

提前致谢。

我尝试了几个选项，但没有一个是有效的。 我希望这个程序能显示数据库的行数。

Answer 1

您似乎正在尝试执行查询来获取

Album

表中的行数，但查询语法可能是问题所在。该错误表明查询解释存在问题。

尝试在查询中使用实体名称而不是表名称。这是代码的修改版本：

Query query = em.createQuery("SELECT COUNT(a) FROM Album a");
Long result = (Long) query.getSingleResult();
System.out.println("Number of rows in Album table: " + result);

此查询使用实体别名 (

a

)，并且应该与 Hibernate 一起使用。尝试一下，看看是否能解决问题。