Mybatis 動態SQL

可以方便的在 sql 語句中實現某些邏輯. 總體說來mybatis 動態SQL 語句主要有以下幾類:
1. if 語句 (簡單的條件判斷)
2. where (主要是用來簡化sql語句中where條件判斷的，能智能的處理 and or ,不必擔心多餘導致語法錯誤)

3. choose (when,otherwize) ,與 jstl 中的choose 很類似.滿足一個條件後其他分支就不再執行
4. set (主要用於update語句)，下面代碼中沒有示例但是用法差不多也很簡單

5. trim (在自己包含的內容前加上某些前綴或者後綴)  與java中的trim要區分開 java中是去除字符兩邊的空格與製表符
6. foreach (在實現in 語句查詢時特別有用)

新建博客表：

create table t_blog(

       id number,

       title varchar(100),

       content varchar(500),

       owner varchar(50)

)

 

insert into t_blog values(1,'標題1','內容1','張三');

insert into t_blog values(2,'標題2','內容2','張三');

insert into t_blog values(3,'標題3','內容3','張三');

insert into t_blog values(4,'標題4','內容4','張三');

 

以下是項目中主要的四個源碼文件

Blog.java

package com.lq.model;

public class Blog {
	private Integer id;
	private String title;
	private String content;
	private String owner;
	
	public Blog() {
		super();
	}
	public Integer getId() {
		return id;
	}
	public void setId(Integer id) {
		this.id = id;
	}
	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;
	}
	public String getOwner() {
		return owner;
	}
	public void setOwner(String owner) {
		this.owner = owner;
	}
	
}

SqlMapConfig.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>
	<!-- 設置別名 -->
	<typeAliases>
		<typeAlias type="com.lq.model.Blog" alias="blog"/>
	</typeAliases>
	
	<!-- 數據源配置   開發環境下設置爲development 可以打印更多的日誌信息  -->
	<environments default="development">
		<environment id="development">
			<!-- 使用jdbc自帶的事務管理器，進行簡單的事務開啓和提交 -->
			<transactionManager type="JDBC" />
			<!-- 使用jdbc自帶的數據庫連接池 -->
			<dataSource type="POOLED">
				<property name="driver" value="com.mysql.jdbc.Driver" />
				<property name="url" value="jdbc:mysql://localhost:3306/test1" />
				<property name="username" value="root" />
				<property name="password" value="root" />
			</dataSource>
		</environment>
	</environments>
	<!-- 配置mapper映射文件 -->
	<mappers>
		<mapper resource="com/lq/model/BlogMapper.xml"/>
	</mappers>
</configuration>

BlogMapper.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.lq.model.BlogMapper">
	<!-- where if 語句使用 -->
	<select id="queryBlog_if" parameterType="blog" resultType="blog">
		select * from t_blog
		<where>
		<!-- 以下使用模糊查詢的兩種方式，#表示使用佔位符傳參；
		$不使用佔位符，直接將參數解析後拼接到SQL中，會引起SQL注入 -->
		<if test="title!=null">
		and title like '%'||#{title}||'%'
		</if>
		<if test="content!=null">
		and content like '%${content}%'
		</if>
		<if test="owner!=null">
		and owner like '%'||#{owner}||'%'
		</if>
		</where>
	</select>
		<!-- choose 語句使用 -->
	<select id="queryBlog_choose" parameterType="blog" resultType="blog">
		select * from t_blog
		<where>
			<choose>
			<when test="title!=null">and title like '%'||#{title}||'%'</when>
			<when test="content!=null">and content like '%${content}%'</when>
			<otherwise>and owner = "張三" </otherwise>
			</choose>
		</where>
	</select>
		<!-- trim 語句使用 -->
	<select id="queryBlog_trim" parameterType="blog" resultType="blog">
		select * from t_blog
		<trim prefix="where" prefixOverrides="and|or">
			<if test="title!=null">
			and title like '%'||#{title}||'%'
			</if>
			<if test="content!=null">
			and content like '%${content}%'
			</if>
			<if test="owner!=null">
			and owner like '%'||#{owner}||'%'
			</if>
		</trim>
	</select>
		<!-- foreach遍歷list 語句使用 -->
	<select id="query_foreach_list" parameterType="list" resultType="blog">
		select * from t_blog where 1=1
		<if test="list!=null">
			and id in
			<foreach collection="list" item="id" open="(" close=")" separator=",">#{id}</foreach>
		</if>
	</select>
			<!-- foreach遍歷數組 語句使用 -->
	<select id="query_foreach_array" parameterType="int" resultType="blog">
		select * from t_blog where 1=1
		<if test="array!=null">
			and id in
			<foreach collection="array" item="id" open="(" close=")" separator=",">#{id}</foreach>
		</if>
	</select>
			<!-- foreach遍歷map 語句使用 -->
	<!-- 
		Map map = new HashMap();
		map.put("owner", "張三");
		map.put("array",array);
		當傳遞map時 ，在sql中使用的都是map的key
	 -->
	<select id="query_foreach_map" parameterType="map" resultType="blog">
		select * from t_blog where 1=1
		<if test="array!=null">
			and id in
			<foreach collection="array" item="id" open="(" close=")" separator=",">#{id}</foreach>
		</if>
		<if test="owner!=null">
			and owner=#{owner}
		</if>
	</select>
</mapper>

BlogTest.java  每個test測試方法對應上面一個Select

package com.lq.test;

import java.io.IOException;
import java.io.Reader;
import java.util.ArrayList;
import java.util.HashMap;
import java.util.List;
import java.util.Map;

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.After;
import org.junit.Before;
import org.junit.Test;

import com.lq.model.Blog;

public class BlogTest {
	SqlSession session =null;
	@Before
	public void before(){
		//加載核心配置文件
		Reader reader;
		try {
			reader = Resources.getResourceAsReader("SqlMapConfig.xml");
			//創建session工廠
			SqlSessionFactory sessionFactory = new SqlSessionFactoryBuilder().build(reader);
			//打開一個和數據庫的會話
			session = sessionFactory.openSession();
		} catch (IOException e) {
			// TODO Auto-generated catch block
			e.printStackTrace();
		}
		
	}
	
	@After
	public void after(){
		//提交事務
		session.commit();
		//關閉連接
		session.close();
	}
	
	@Test
	public void testQuery_if() throws IOException{
		Blog blog=new Blog();
		blog.setTitle("標題");
		blog.setContent("內容");
		List<Blog> list=session.selectList("com.lq.model.BlogMapper.queryBlog_if", blog);
		for (Blog blog2 : list) {
			System.out.println(blog2.getId()+"-----"+blog2.getTitle()+"-----"+
					blog2.getContent()+"-----"+blog2.getOwner());
		}
	}
	@Test
	public void testQuery_choose() throws IOException{
		Blog blog=new Blog();
		List<Blog> list=session.selectList("com.lq.model.BlogMapper.queryBlog_choose", blog);
		for (Blog blog2 : list) {
			System.out.println(blog2.getId()+"-----"+blog2.getTitle()+"-----"+
					blog2.getContent()+"-----"+blog2.getOwner());
		}
	}
	@Test
	public void testQuery_trim() throws IOException{
		Blog blog=new Blog();
		blog.setTitle("標題");
		blog.setContent("內容");
		List<Blog> list=session.selectList("com.lq.model.BlogMapper.queryBlog_trim", blog);
		for (Blog blog2 : list) {
			System.out.println(blog2.getId()+"-----"+blog2.getTitle()+"-----"+
					blog2.getContent()+"-----"+blog2.getOwner());
		}
	}
	@Test
	public void queryForeachList() throws IOException{
		List list=new ArrayList();
		list.add(1);
		list.add(2);
		List<Blog> blogs=session.selectList("com.lq.model.BlogMapper.query_foreach_list", list);
		for (Blog blog2 : blogs) {
			System.out.println(blog2.getId()+"-----"+blog2.getTitle()+"-----"+
					blog2.getContent()+"-----"+blog2.getOwner());
		}
	}
	@Test
	public void queryForeachArray() throws IOException{
		int[] array={1,2};
		List<Blog> blogs=session.selectList("com.lq.model.BlogMapper.query_foreach_array", array);
		for (Blog blog2 : blogs) {
			System.out.println(blog2.getId()+"-----"+blog2.getTitle()+"-----"+
					blog2.getContent()+"-----"+blog2.getOwner());
		}
	}
	@Test
	public void queryForeachMap() throws IOException{
		Map map = new HashMap();
		int[] array={1,2};
		map.put("owner", "張三");
		map.put("array",array);
		List<Blog> blogs=session.selectList("com.lq.model.BlogMapper.query_foreach_map", map);
		for (Blog blog2 : blogs) {
			System.out.println(blog2.getId()+"-----"+blog2.getTitle()+"-----"+
					blog2.getContent()+"-----"+blog2.getOwner());
		}
	}

}