Hibernate（34）Hibernate的别名（Alias）是什么？

Victor3562026-01-10 8:10

Hibernate的别名（Alias）

在Hibernate中，使用别名（Alias）可以为查询中的实体或属性指定一个简短的替代名称。别名的使用有助于简化查询语句，特别是在多表联接或复杂查询中。此外，别名还可以用于在相同查询中引用同一个实体的多个实例。

使用别名的示例代码

实体类定义

我们继续使用之前定义的Person和Address实体类。

Person类
java 复制代码 
package com.example.domain;

import javax.persistence.*;

@Entity
@Table(name = "person")
public class Person {

    @Id
    @GeneratedValue(strategy = GenerationType.IDENTITY)
    private Long id;

    @Column(name = "name")
    private String name;

    @Column(name = "age")
    private int age;

    public Person() {}

    public Person(String name, int age) {
        this.name = name;
        this.age = age;
    }

    // Getters 和 Setters

    public Long getId() {
        return id;
    }

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

    public String getName() {
        return name;
    }

    public void setName(String name) {
        this.name = name;
    }

    public int getAge() {
        return age;
    }

    public void setAge(int age) {
        this.age = age;
    }
}
Address类
java 复制代码 
package com.example.domain;

import javax.persistence.*;

@Entity
@Table(name = "address")
public class Address {

    @Id
    @GeneratedValue(strategy = GenerationType.IDENTITY)
    private Long id;

    @Column(name = "street")
    private String street;

    @ManyToOne
    @JoinColumn(name = "person_id", nullable = false)
    private Person person;

    public Address() {}

    public Address(String street, Person person) {
        this.street = street;
        this.person = person;
    }

    // Getters 和 Setters

    public Long getId() {
        return id;
    }

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

    public String getStreet() {
        return street;
    }

    public void setStreet(String street) {
        this.street = street;
    }

    public Person getPerson() {
        return person;
    }

    public void setPerson(Person person) {
        this.person = person;
    }
}

Hibernate配置文件 hibernate.cfg.xml

xml 复制代码 
<!DOCTYPE hibernate-configuration PUBLIC
        "-//Hibernate/Hibernate Configuration DTD 3.0//EN"
        "http://hibernate.sourceforge.net/hibernate-configuration-3.0.dtd">
<hibernate-configuration>
    <session-factory>
        <!-- 数据库连接配置 -->
        <property name="hibernate.connection.driver_class">com.mysql.cj.jdbc.Driver</property>
        <property name="hibernate.connection.url">jdbc:mysql://localhost:3306/your_database</property>
        <property name="hibernate.connection.username">your_username</property>
        <property name="hibernate.connection.password">your_password</property>

        <!-- Hibernate 属性配置 -->
        <property name="hibernate.dialect">org.hibernate.dialect.MySQLDialect</property>
        <property name="hibernate.show_sql">true</property>
        <property name="hibernate.format_sql">true</property>
        <property name="hibernate.hbm2ddl.auto">update</property>

        <!-- 映射类 -->
        <mapping class="com.example.domain.Person"/>
        <mapping class="com.example.domain.Address"/>
    </session-factory>
</hibernate-configuration>

HibernateUtil类

java 复制代码 
import org.hibernate.SessionFactory;
import org.hibernate.cfg.Configuration;

public class HibernateUtil {
    private static final SessionFactory sessionFactory;

    static {
        try {
            // 从配置文件创建SessionFactory
            sessionFactory = new Configuration().configure("hibernate.cfg.xml").buildSessionFactory();
        } catch (Throwable ex) {
            // 记录启动失败的错误
            System.err.println("Initial SessionFactory creation failed." + ex);
            throw new ExceptionInInitializerError(ex);
        }
    }

    public static SessionFactory getSessionFactory() {
        return sessionFactory;
    }
}

使用别名的示例

插入示例数据

java 复制代码 
import org.hibernate.Session;
import org.hibernate.SessionFactory;
import org.hibernate.Transaction;

public class HibernateInsertData {
    public static void main(String[] args) {
        // 获取SessionFactory
        SessionFactory sessionFactory = HibernateUtil.getSessionFactory();

        // 插入示例数据
        insertSampleData(sessionFactory);

        // 关闭SessionFactory
        sessionFactory.close();
    }

    private static void insertSampleData(SessionFactory sessionFactory) {
        Session session = sessionFactory.openSession();
        Transaction transaction = session.beginTransaction();
        try {
            Person person1 = new Person("John Doe", 30);
            Person person2 = new Person("Jane Doe", 28);

            session.save(person1);
            session.save(person2);

            Address address1 = new Address("123 Main St", person1);
            Address address2 = new Address("456 Oak St", person2);

            session.save(address1);
            session.save(address2);

            transaction.commit();
            System.out.println("Inserted sample data");
        } catch (Exception e) {
            if (transaction != null) {
                transaction.rollback();
            }
            e.printStackTrace();
        } finally {
            if (session != null) {
                session.close();
            }
        }
    }
}

使用别名进行查询

查询Person及其Address信息

使用别名来简化多表联接查询。

java 复制代码 
import org.hibernate.Session;
import org.hibernate.SessionFactory;
import org.hibernate.query.criteria.HibernateCriteriaBuilder;
import org.hibernate.query.criteria.JpaCriteriaQuery;
import javax.persistence.criteria.Join;
import javax.persistence.criteria.Root;
import java.util.List;

public class HibernateAliasQueryExample {
    public static void main(String[] args) {
        // 获取SessionFactory
        SessionFactory sessionFactory = HibernateUtil.getSessionFactory();

        // 使用别名查询Person及其Address信息
        queryPersonAndAddress(sessionFactory);

        // 关闭SessionFactory
        sessionFactory.close();
    }

    private static void queryPersonAndAddress(SessionFactory sessionFactory) {
        Session session = sessionFactory.openSession();
        try {
            HibernateCriteriaBuilder criteriaBuilder = session.getCriteriaBuilder();
            JpaCriteriaQuery<Object[]> criteriaQuery = criteriaBuilder.createQuery(Object[].class);
            Root<Person> personRoot = criteriaQuery.from(Person.class);
            Join<Person, Address> addressJoin = personRoot.join("address");

            // 使用别名
            criteriaQuery.multiselect(personRoot.get("name").alias("personName"), addressJoin.get("street").alias("addressStreet"));

            List<Object[]> results = session.createQuery(criteriaQuery).getResultList();
            System.out.println("Query Person and Address:");
            for (Object[] row : results) {
                String personName = (String) row[0];
                String addressStreet = (String) row[1];
                System.out.println(personName + " lives at " + addressStreet);
            }
        } catch (Exception e) {
            e.printStackTrace();
        } finally {
            if (session != null) {
                session.close();
            }
        }
    }
}

使用别名的详细解释

  1. 插入示例数据 ：向数据库中插入两个Person对象和两个Address对象供查询使用。

    java 复制代码 
    public class HibernateInsertData {
    public static void main(String[] args) {
        // 获取SessionFactory
        SessionFactory sessionFactory = HibernateUtil.getSessionFactory();

        // 插入示例数据
        insertSampleData(sessionFactory);

        // 关闭SessionFactory
        sessionFactory.close();
    }

    private static void insertSampleData(SessionFactory sessionFactory) {
        Session session = sessionFactory.openSession();
        Transaction transaction = session.beginTransaction();
        try {
            Person person1 = new Person("John Doe", 30);
            Person person2 = new Person("Jane Doe", 28);

            session.save(person1);
            session.save(person2);

            Address address1 = new Address("123 Main St", person1);
            Address address2 = new Address("456 Oak St", person2);

            session.save(address1);
            session.save(address2);

            transaction.commit();
            System.out.println("Inserted sample data");
        } catch (Exception e) {
            if (transaction != null) {
                transaction.rollback();
            }
            e.printStackTrace();
        } finally {
            if (session != null) {
                session.close();
            }
        }
    }
}

  2. 使用别名查询Person及其Address信息：我们使用别名来简化联接查询并投影特定的属性。

    java 复制代码 
    public class HibernateAliasQueryExample {
    public static void main(String[] args) {
        // 获取SessionFactory
        SessionFactory sessionFactory = HibernateUtil.getSessionFactory();

        // 使用别名查询Person及其Address信息
        queryPersonAndAddress(sessionFactory);

        // 关闭SessionFactory
        sessionFactory.close();
    }

    private static void queryPersonAndAddress(SessionFactory sessionFactory) {
        Session session = sessionFactory.openSession();
        try {
            HibernateCriteriaBuilder criteriaBuilder = session.getCriteriaBuilder();
            JpaCriteriaQuery<Object[]> criteriaQuery = criteriaBuilder.createQuery(Object[].class);
            Root<Person> personRoot = criteriaQuery.from(Person.class);
            Join<Person, Address> addressJoin = personRoot.join("address");
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