Mybatis入门--关联查询一对一

public class Article {

private int id;
private Customer customer;
private String title;
private String content;

public int getId() {
return id;
}

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

public Customer getCustomer() {
return customer;
}

public void setCustomer(Customer customer) {
this.customer = customer;
}

public String getTitle() {
return title;
}

public void setTitle(String title) {
this.title = title;
}

public String getContent() {
return content;
}

public void setContent(String content) {
this.content = content;
}
}

<?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="org.lezg.web.mapper.ArticleMapper">

<!-- 数据库字段与实体对象的映射关系 -->
<resultMap id="customerResultMap" type="Customer">
<id column="id" property="id"/>
<result column="name" property="name"/>
<result column="contact" property="contact"/>
<result column="telephone" property="telephone"/>
<result column="email" property="email"/>
</resultMap>

<!-- association标签来解决一对一的关联查询 -->
<resultMap id="articleResultMap" type="Article">
<id column="id" property="id"/>
<result column="title" property="title"/>
<result column="content" property="content"/>
<association property="customer" column="customer_id" javaType="Customer" resultMap="customerResultMap"/>
</resultMap>

<!-- 查询Article by id -->
<select id="getArticle" parameterType="int" resultMap="articleResultMap">
SELECT * from customer c, article a WHERE c.id = a.customer_id and a.id = #{id}
</select>
<!-- 查询所有Article -->
<select id="getArticles" resultMap="articleResultMap">
SELECT * from article a, customer c where a.customer_id = c.id
</select>
</mapper>

public interface ArticleMapper {

/**
* 查询Article by id
* @param id
* @return
*/
Article getArticle(int id);

/**
* 查询所有Article
* @return
*/
List<Article> getArticles();
}

<?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>
<!-- 设置别名 -->
<typeAliases>
<typeAlias type="org.lezg.web.entity.Customer" alias="Customer"/>
<typeAlias type="org.lezg.web.entity.Article" alias="Article"/>
</typeAliases>

<environments default="development">
<environment id="development">
<transactionManager type="JDBC"/>
<dataSource type="POOLED">
<property name="driver" value="com.mysql.jdbc.Driver"/>
<property name="url" value="jdbc:mysql://localhost:3306/lezgweb"/>
<property name="username" value="root"/>
<property name="password" value="root"/>
</dataSource>
</environment>
</environments>
<!-- 映射文件 -->
<mappers>
<mapper resource="mapper/customerMapper.xml"/>
<mapper resource="mapper/articleMapper.xml"/>
</mappers>
</configuration>

@org.junit.Test
public void getArticle(){
SqlSession session = getSession();
ArticleMapper articleMapper = session.getMapper(ArticleMapper.class);
Article article = articleMapper.getArticle(1);
System.out.println(article.getTitle());
System.out.println(article.getContent());
System.out.println(article.getCustomer().getContact());
closeSession(session);
}

@org.junit.Test
public void getArticles(){
SqlSession session = getSession();
ArticleMapper articleMapper = session.getMapper(ArticleMapper.class);
List<Article> articles = articleMapper.getArticles();
for (Article article : articles) {
System.out.println(article.getTitle());
System.out.println(article.getContent());
System.out.println(article.getCustomer().getContact());
}
}