Introduction to ORM mapping using annotations

In the past two years, more projects have used annotations for ORM mapping of some relatively stable entity classes, which makes programming more concise and simple. In fact, there are not many changes in the operation process between using annotations for ORM mapping and using xml for mapping. The main steps are: importing packages, writing annotated entity classes, writing core configuration files, and writing test classes.

The project code has been uploaded to GitHub: Project name: HibernateUseAnnotation

The entire project structure is as follows:

1. Guide package

　 The author is using the MySQL database , so the imported data package is as shown below:

2. Write entity classes

　 The annotations used for mapping are basically defined in the javax.persistence.* package. The main ones I commonly use are the following four :

@Entity annotation marks this class as an entity.

The @Table annotation specifies the name of the table where the data for this entity is to be retained. If you do not use the @Table annotation, hibernate will use the class name as the table name by default.

@Id annotation marks the identifier of this entity.

@Column annotation specifies the details of the column of this attribute or field. If the @Column annotation is not specified, the property name will be used as the column name bydefault.

 1 package com.rocky.domain; 2  3 import javax.persistence.Entity; 4 import javax.persistence.Id; 5 import javax.persistence.Table; 6  7 @Entity 8 @Table(name = "tb_user") 9 public class User10 {11     @Id12     private Integer uId;13     private String uName;14     private Integer uAge;15     public User()16     {17         super();18     }19     @Override20     public String toString()21     {22         return "User [uId=" + uId + ", uName=" + uName + ", uAge=" + uAge + "]";23     }24     public Integer getuId()25     {26         return uId;27     }28     public void setuId(Integer uId)29     {30         this.uId = uId;31     }32     public String getuName()33     {34         return uName;35     }36     public void setuName(String uName)37     {38         this.uName = uName;39     }40     public Integer getuAge()41     {42         return uAge;43     }44     public void setuAge(Integer uAge)45     {46         this.uAge = uAge;47     }48 }

3. Write the core configuration file

The configuration file using annotations is basically the same as the configuration file mapped by xml, but the attribute used when introducing external mapping is class instead of resource attribute.

 1 <?xml version=&#39;1.0&#39; encoding=&#39;UTF-8&#39;?> 2 <!DOCTYPE hibernate-configuration PUBLIC 3           "-//Hibernate/Hibernate Configuration DTD 3.0//EN" 4           "http://hibernate.sourceforge.net/hibernate-configuration-3.0.dtd"> 5  6 <hibernate-configuration> 7     <session-factory> 8  9         <!--指定数据库的参数  -->10         <property name="hibernate.dialect">org.hibernate.dialect.MySQLDialect</property>11         <property name="hibernate.connection.driver_class">com.mysql.jdbc.Driver</property>12         <property name="hibernate.connection.url">jdbc:mysql://192.168.100.100:3306/test</property>13         <property name="hibernate.connection.username">root</property>14         <property name="hibernate.connection.password">1</property>15         16         <!--指定hibernate是否显式SQL语句及其格式化  -->17         <property name="hibernate.show_sql">true</property>18         <property name="hibernate.format_sql">true</property>19         20         <!--指定表的生成方式-即是否由hibernate自动创建表，其取值为：create-drop、21          create、validate、update-->22         <property name="hibernate.hbm2ddl.auto">update</property>23         24         <!--引入 ORM配置文件 -->25         <mapping class="com.rocky.domain.User"/>26     </session-factory>27 28 </hibernate-configuration>

4. Write test class

 1 package com.rocky.testdriver; 2  3 import org.hibernate.Session; 4 import org.hibernate.SessionFactory; 5 import org.hibernate.Transaction; 6 import org.hibernate.cfg.Configuration; 7  8 import com.rocky.domain.User; 9 10 public class TestDriver11 {12 13     public static void main(String[] args)14     {15         // 加载配置文件16         Configuration cfg = new Configuration();17         cfg.configure();18         // 创建会话工厂19         SessionFactory factory = cfg.buildSessionFactory();20         // 获取非线程绑定会话21         Session session = factory.openSession();22         // 开启事务23         Transaction tx = session.beginTransaction();24         // 创建User对象25         User user = new User();26         user.setuId(1);27         user.setuName("rocky");28         user.setuAge(28);29 30         // 将数据插入数据库31         session.save(user);32 33         // 提交事务34         tx.commit();35         // 关闭会话36         session.close();37     }38 39 }

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