使用Hibernate时如何使用注解防止Mysql中的重复记录

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问题描述

这是我在 Java Hibernate 中的第二天.我正在从这个 YouTube 教程中学习:

It's my day 2 in Java Hibernate. I'm learning form this YouTube tutorial:

我仔细地遵循每一步.我的问题是我可以多次推送相同的记录:

I'm carefully following each and every step. My problem is that I'm able to push same record many times:

mysql> select * from Alien;
+------+-------+--------+
| aid  | aname | acolor |
+------+-------+--------+
|  101 | Navin | Green  |
|  101 | Navin | Green  |
|  101 | Navin | Green  |
|  101 | Navin | Green  |
|  101 | Navin | Green  |
|  101 | Navin | Green  |
|  101 | Navin | Green  |
+------+-------+--------+
7 rows in set (0.00 sec)

这是我的文件.

hibernate.cfg.xml

<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE hibernate-configuration PUBLIC
        "-//Hibernate/Hibernate Configuration DTD 3.0//EN"
        "http://www.hibernate.org/dtd/hibernate-configuration-3.0.dtd">
<hibernate-configuration>
    <session-factory>
        <property name="hibernate.connection.driver_class">com.mysql.cj.jdbc.Driver</property>
        <property name="hibernate.connection.password">cosmonauts</property>
        <property name="hibernate.connection.url">jdbc:mysql://localhost:3306/testdb</property>
        <property name="hibernate.connection.username">root</property>
        <property name="hibernate.dialect">org.hibernate.dialect.MySQLDialect</property>
        <property name="hibernate.hbm2ddl.auto">
            update
        </property>
        <property name="show_sql=true"></property>
    </session-factory>
</hibernate-configuration>

Alien.java

import javax.persistence.Entity;
import javax.persistence.Id;

@Entity
public class Alien {  // POJO
    
    @Id
    private int aid;
    private String aname;
    private String acolor;
    
    ... //getters and setters
}

App.java//主类

import org.hibernate.Session;
import org.hibernate.SessionFactory;
import org.hibernate.Transaction;
import org.hibernate.boot.registry.StandardServiceRegistry;
import org.hibernate.boot.registry.StandardServiceRegistryBuilder;
import org.hibernate.cfg.Configuration;

public class App {

    public static void main(String[] args) {
        Alien telusko = new Alien();
        telusko.setAid(101);
        telusko.setAname("Navin");
        telusko.setAcolor("Green");
        
        Configuration configuration = new Configuration().configure().addAnnotatedClass(Alien.class);
        
        StandardServiceRegistry reg = new StandardServiceRegistryBuilder().applySettings(configuration.getProperties()).build();
        SessionFactory sf = configuration.buildSessionFactory(reg);
        
        Session session = sf.openSession();
        
        Transaction tx = session.beginTransaction();
        session.save(telusko);
        tx.commit();
    }
}

pom.xml

<project xmlns="http://maven.apache.org/POM/4.0.0" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 https://maven.apache.org/xsd/maven-4.0.0.xsd">
  <modelVersion>4.0.0</modelVersion>
  <groupId>com.student.sample</groupId>
  <artifactId>StudentSystem</artifactId>
  <version>0.0.1-SNAPSHOT</version>
  <dependencies>
    <dependency>
        <groupId>mysql</groupId>
        <artifactId>mysql-connector-java</artifactId>
        <version>8.0.26</version>
    </dependency>
    <dependency>
        <groupId>org.hibernate</groupId>
        <artifactId>hibernate-core</artifactId>
        <version>5.5.6.Final</version>
    </dependency>
</dependencies>
</project>

我是不是误会了什么.请纠正我的错误.

Did I misunderstand something. Please correct my mistake.

在控制台上我得到这个:

On console I'm getting this:

Aug 19, 2021 10:43:44 PM org.hibernate.Version logVersion
INFO: HHH000412: Hibernate ORM core version 5.5.6.Final
Aug 19, 2021 10:43:45 PM org.hibernate.annotations.common.reflection.java.JavaReflectionManager <clinit>
INFO: HCANN000001: Hibernate Commons Annotations {5.1.2.Final}
Aug 19, 2021 10:43:45 PM org.hibernate.engine.jdbc.connections.internal.DriverManagerConnectionProviderImpl configure
WARN: HHH10001002: Using Hibernate built-in connection pool (not for production use!)
Aug 19, 2021 10:43:45 PM org.hibernate.engine.jdbc.connections.internal.DriverManagerConnectionProviderImpl buildCreator
INFO: HHH10001005: using driver [com.mysql.cj.jdbc.Driver] at URL [jdbc:mysql://localhost:3306/testdb]
Aug 19, 2021 10:43:45 PM org.hibernate.engine.jdbc.connections.internal.DriverManagerConnectionProviderImpl buildCreator
INFO: HHH10001001: Connection properties: {password=****, user=root}
Aug 19, 2021 10:43:45 PM org.hibernate.engine.jdbc.connections.internal.DriverManagerConnectionProviderImpl buildCreator
INFO: HHH10001003: Autocommit mode: false
Aug 19, 2021 10:43:45 PM org.hibernate.engine.jdbc.connections.internal.DriverManagerConnectionProviderImpl$PooledConnections <init>
INFO: HHH000115: Hibernate connection pool size: 20 (min=1)
Aug 19, 2021 10:43:45 PM org.hibernate.dialect.Dialect <init>
INFO: HHH000400: Using dialect: org.hibernate.dialect.MySQLDialect
Aug 19, 2021 10:43:45 PM org.hibernate.resource.transaction.backend.jdbc.internal.DdlTransactionIsolatorNonJtaImpl getIsolatedConnection
INFO: HHH10001501: Connection obtained from JdbcConnectionAccess [org.hibernate.engine.jdbc.env.internal.JdbcEnvironmentInitiator$ConnectionProviderJdbcConnectionAccess@27e7c77f] for (non-JTA) DDL execution was not in auto-commit mode; the Connection 'local transaction' will be committed and the Connection will be set into auto-commit mode.
Aug 19, 2021 10:43:45 PM org.hibernate.engine.transaction.jta.platform.internal.JtaPlatformInitiator initiateService
INFO: HHH000490: Using JtaPlatform implementation: [org.hibernate.engine.transaction.jta.platform.internal.NoJtaPlatform]

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Hibernate

使用Hibernate时如何使用注解防止Mysql中的重复记录

问题描述

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