介紹

通過mybatis提供的各種標籤方法實現動態拼接sql

Mybatis動態sql---<sql>與<include>

<!-- 使用include標籤載入sql片段；refid是sql片段id -->
<sql id="select">
	select * from user
</sql>

<!-- 
    在需要使用的地方使用include標籤使用  在後面的動態sql標籤中會使用到 
    這裡的refid與<sql>中的select是一一對應的
-->
<include refid="select"/>
 

Mybatis動態sql---<if>標籤

mapper介面

public List<User> findUserBySexAndName(User user);

<!-- 
    動態SQL配置
	有<if> 這裡是可以做一個判斷，配置上sql的值
	<where> 這裡是可以去掉語句中的就第一個前and
-->
<!-- 根據性別和名字來查詢 -->
<select id="findUserBySexAndName" parameterType="User" resultType="User">
	 <include refid="select"/>
	 <where>
	 	<if test="sex != null and sex !=''">
	 		and sex = #{sex}
	 	</if>
	 	<if test="username!=null and username!=''">
	 		and username like '%${username}%'
	 	</if>
	</where>
</select>
 

測試程式碼

@Test
public void testFindUserBySexAndName() throws Exception {
	String resource = "SqlMapConfig.xml";
	InputStream resourceAsStream = Resources.getResourceAsStream(resource);
	SqlSessionFactory sqlSessionFactory = new SqlSessionFactoryBuilder().build(resourceAsStream);
	SqlSession sqlSession = sqlSessionFactory.openSession();
	UserMapper mapper = sqlSession.getMapper(UserMapper.class);
	User user = new User();
	user.setSex("0");
	user.setUsername("lin");
	List<User> list = mapper.findUserBySexAndName(user);
	for (User user2 : list) {
		System.out.println(user2);
	}
}
	
 

資料庫中的資料

測試效果

Mybatis動態sql---<foreach>

<!-- findUserByUserVo輸出類 -->
<select id="findUserByUserVolist" parameterType="UserVo" resultType="User">
 	<include refid="select"/>
 	<!-- foreach標籤，進行遍歷 -->
	<!-- collection：遍歷的集合，這裡是QueryVo的ids屬性 -->
	<!-- item：遍歷的專案，可以隨便寫，，但是和後面的#{}裡面要一致 -->
	<!-- open：在前面新增的sql片段 -->
	<!-- close：在結尾處新增的sql片段 -->
	<!-- separator：指定遍歷的元素之間使用的分隔符 -->
 	<where>
 		id in
 		<foreach collection="list" item="id" open="(" close=")" separator=",">
 			#{id}
 		</foreach>
 	</where>
 </select>

UserVo程式碼

package com.janson.vo;

import java.io.Serializable;
import java.util.List;

import com.janson.pojo.User;

public class UserVo implements Serializable {
	private static final long serialVersionUID = 1L;
	private User user;
	private List<Integer> list;
	private Integer[] ids;

。。。省略了get和set
}

mapper程式碼

public List<User> findUserByUserVolist(UserVo vo);

測試程式碼

@Test
public void testfindUserByUserVolist() throws Exception {
	String resource = "SqlMapConfig.xml";
	InputStream resourceAsStream = Resources.getResourceAsStream(resource);
	SqlSessionFactory sqlSessionFactory = new SqlSessionFactoryBuilder().build(resourceAsStream);
	SqlSession sqlSession = sqlSessionFactory.openSession();
	UserMapper mapper = sqlSession.getMapper(UserMapper.class);
	UserVo vo = new  UserVo();
	List l = new ArrayList<>();
	l.add("1");
	l.add("3");
	l.add("4");
	vo.setList(l);
	List<User> list = mapper.findUserByUserVolist(vo);
	for (User user : list) {
		System.out.println(user);
	}
}

測試結果