本实例使用用户(User)和博客(Post)的例子做说明: 一个用户可以有多个博客, 一个博客只对应一个用户
一. 例子(本实体采用maven构建):
1. 代码结构图:
2. 数据库:
t_user 用户表:
CREATE TABLE `t_user` ( `t_id` int(11) NOT NULL AUTO_INCREMENT, `t_name` varchar(26) NOT NULL, `t_age` int(11) NOT NULL, PRIMARY KEY (`t_id`) ) ENGINE=InnoDB AUTO_INCREMENT=3 DEFAULT CHARSET=utf8;
post 博客表:
CREATE TABLE `t_post` ( `id` int(11) NOT NULL AUTO_INCREMENT, `url` varchar(255) NOT NULL, `uid` int(11) NOT NULL, PRIMARY KEY (`id`), KEY `u_id` (`uid`), CONSTRAINT `u_id` FOREIGN KEY (`uid`) REFERENCES `t_user` (`t_id`) ) ENGINE=InnoDB AUTO_INCREMENT=5 DEFAULT CHARSET=utf8;
3. 博客实体:
/** * 博客类 */ public class Post { private Integer id; private String url; private Integer uid; private User user; public User getUser() { return user; } public void setUser(User user) { this.user = user; } public Integer getId() { return id; } public void setId(Integer id) { this.id = id; } public String getUrl() { return url; } public void setUrl(String url) { this.url = url; } public Integer getUid() { return uid; } public void setUid(Integer uid) { this.uid = uid; } @Override public String toString() { return "Post{" + "id=" + id + ", url='" + url + '\'' + ", uid=" + uid + ", user=" + user + '}'; } }
4. 用户实体:
/** * 用户类 */ public class User { private String tName; private Integer tAge; private Integer tid; private List<Post> posts; public List<Post> getPosts() { return posts; } public void setPosts(List<Post> posts) { this.posts = posts; } public Integer getTid() { return tid; } public void setTid(Integer tid) { this.tid = tid; } public String gettName() { return tName; } public void settName(String tName) { this.tName = tName; } public Integer gettAge() { return tAge; } public void settAge(Integer tAge) { this.tAge = tAge; } @Override public String toString() { return "User{" + "tName='" + tName + '\'' + ", tAge=" + tAge + ", tid=" + tid + ", posts=" + posts + '}'; } }
5. 一对多实体配置: UserMapper.xml
<?xml version="1.0" encoding="UTF-8"?> <!DOCTYPE mapper PUBLIC "-//mybatis.org//DTD Mapper 3.0//EN" "http://mybatis.org/dtd/mybatis-3-mapper.dtd"> <mapper namespace="com.yiibai.mybatis.models.UserMapper"> <!-- 根据id查询User, 关联将Post查询出来 --> <select id="getUser" resultMap="getUsersMap"> select * from t_user u,t_post p where u.t_id=p.uid and u.t_id=#{t_id} </select> <resultMap type="User" id="getUsersMap"> <id column="t_id" property="tid"></id> <result column="t_name" property="tName"/> <result column="t_age" property="tAge"/> <!-- 一对多的关系 --> <!-- property: 指的是集合属性的值, ofType:指的是集合中元素的类型 --> <collection property="posts" ofType="Post"> <id column="id" property="id"/> <result column="url" property="url"/> <result column="uid" property="uid"/> </collection> </resultMap> </mapper>
6. 多对一实体配置:PostMapper.xml
<?xml version="1.0" encoding="UTF-8"?> <!DOCTYPE mapper PUBLIC "-//mybatis.org//DTD Mapper 3.0//EN" "http://mybatis.org/dtd/mybatis-3-mapper.dtd"> <mapper namespace="com.yiibai.mybatis.models.PostMapper"> <!-- 根据id查询Post, 关联将User查询出来 --> <select id="getPost" resultMap="getPostMap"> select * from t_user u,t_post p where u.t_id=p.uid and p.id=#{id} </select> <resultMap type="Post" id="getPostMap"> <id column="id" property="id"></id> <result column="url" property="url"/> <result column="uid" property="uid"/> <!-- 多对一的关系 --> <!-- property: 指的是属性的值, javaType:指的是属性的类型--> <association property="user" javaType="User"> <id column="t_id" property="tid"/> <result column="t_name" property="tName"/> <result column="t_age" property="tAge"/> </association> </resultMap> </mapper>
7. mybatis配置文件: Configure.xml
<?xml version="1.0" encoding="UTF-8"?> <!DOCTYPE configuration PUBLIC "-//mybatis.org//DTD Config 3.0//EN" "http://mybatis.org/dtd/mybatis-3-config.dtd"> <configuration> <properties resource="sql.properties"/> <settings> <setting name="mapUnderscoreToCamelCase" value="true"/> </settings> <typeAliases> <typeAlias alias="User" type="models.User"/> <typeAlias alias="Post" type="models.Post"/> </typeAliases> <environments default="development"> <environment id="development"> <transactionManager type="JDBC"/> <dataSource type="POOLED"> <property name="driver" value="${jdbc.driverClassName}"/> <property name="url" value="${jdbc.url}"/> <property name="username" value="${jdbc.username}"/> <property name="password" value="${jdbc.password}"/> </dataSource> </environment> </environments> <mappers> <!-- // power by http://www.yiibai.com --> <mapper resource="UserMapper"/> <mapper resource="PostMapper"/> </mappers> </configuration>
8. 测试文件:
import models.Post; import models.User; import org.apache.ibatis.io.Resources; import org.apache.ibatis.session.SqlSession; import org.apache.ibatis.session.SqlSessionFactory; import org.apache.ibatis.session.SqlSessionFactoryBuilder; import org.junit.Before; import java.io.InputStream; public class Test { private SqlSessionFactory ssf; @Before public void initSF() throws Exception { String resource = "Configure"; InputStream inputStream = Resources.getResourceAsStream(resource); ssf = new SqlSessionFactoryBuilder().build(inputStream); } @org.junit.Test //多对一关联查询 public void selectPostById() { SqlSession session = ssf.openSession(); User user = session.selectOne("com.yiibai.mybatis.models.UserMapper.getUser", 1); System.out.println(user.toString()); session.close(); } @org.junit.Test //一对多关联查询 public void selectUserById() { SqlSession session = ssf.openSession(); Post post = session.selectOne("com.yiibai.mybatis.models.PostMapper.getPost", 1); System.out.println(post.toString()); session.close(); } }
9:maven配置
<dependencies> <!--dependency> <groupId>com.ggband</groupId> <artifactId>[the artifact id of the block to be mounted]</artifactId> <version>1.0-SNAPSHOT</version> </dependency--> <dependency> <groupId>mysql</groupId> <artifactId>mysql-connector-java</artifactId> <version>5.1.31</version> </dependency> <dependency> <groupId>org.mybatis</groupId> <artifactId>mybatis</artifactId> <version>3.4.6</version> </dependency> <dependency> <groupId>org.testifyproject.junit4</groupId> <artifactId>junit4-core</artifactId> <version>1.0.3</version> </dependency> </dependencies>
ggband