MyBatis(7)——動態SQL
阿新 • • 發佈:2020-12-13
動態SQL指的是根據不同的查詢條件 , 生成不同的Sql語句。
MyBatis 採用功能強大的基於 OGNL 的表示式來淘汰其它大部分元素。
-------------------------------
- if
- choose (when, otherwise)
- trim (where, set)
- foreach
-------------------------------
1.1 環境搭建
搭建資料庫
CREATE TABLE `blog` (
`id` varchar(50) NOT NULL COMMENT '部落格id' ,
`title` varchar(100) NOT NULL COMMENT '部落格標題',
`author` varchar(30) NOT NULL COMMENT '部落格作者',
`create_time` datetime NOT NULL COMMENT '建立時間',
`views` int(30) NOT NULL COMMENT '瀏覽量'
) ENGINE=InnoDB DEFAULT CHARSET=utf8
構建實體類
@Data
public class Blog {
private String id;
private String title;
private String author;
private Date createTime;
private int views;
}
編寫介面類
public interface BlogMapper {
}
編寫Mapper.xml檔案
<?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.kuang.mapper.BlogMapper">
</mapper>
核心檔案的配置(mybatis-config.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>
<!-- 引入外部配置檔案-->
<properties resource="db.properties"/>
<settings>
<!-- 標椎日誌輸出-->
<setting name="logImpl" value="LOG4J"/>
<!-- 駝峰對映-->
<setting name="mapUnderscoreToCamelCase" value="true"/>
</settings>
<environments default="development">
<environment id="development">
<transactionManager type="JDBC"/>
<dataSource type="POOLED">
<property name="driver" value="${driver}"/>
<property name="url" value="${url}"/>
<property name="username" value="${username}"/>
<property name="password" value="${password}"/>
</dataSource>
</environment>
</environments>
<!-- 繫結介面-->
<mappers>
<mapper class="com.xxxx.dao.BlogMapper"/>
</mappers>
</configuration>
日誌檔案配置log4j.properties
#將等級為DEBUG的日誌資訊輸出到console和file這兩個目的地,console和file的定義在下面的程式碼
log4j.rootLogger=DEBUG,console,file
#控制檯輸出的相關設定
log4j.appender.console = org.apache.log4j.ConsoleAppender
log4j.appender.console.Target = System.out
log4j.appender.console.Threshold=DEBUG
log4j.appender.console.layout = org.apache.log4j.PatternLayout
log4j.appender.console.layout.ConversionPattern=[%c]-%m%n
#檔案輸出的相關設定
log4j.appender.file = org.apache.log4j.RollingFileAppender
log4j.appender.file.File=./log/xxxx.log
log4j.appender.file.MaxFileSize=10mb
log4j.appender.file.Threshold=DEBUG
log4j.appender.file.layout=org.apache.log4j.PatternLayout
log4j.appender.file.layout.ConversionPattern=[%p][%d{yy-MM-dd}][%c]%m%n
#日誌輸出級別
log4j.logger.org.mybatis=DEBUG
log4j.logger.java.sql=DEBUG
log4j.logger.java.sql.Statement=DEBUG
log4j.logger.java.sql.ResultSet=DEBUG
log4j.logger.java.sql.PreparedStatement=DEBUG
db.properties檔案的配置
driver=com.mysql.jdbc.Driver
url=jdbc:mysql://localhost:3306/mybatis?useSSL=true&useUnicode=true&characterEncoding=utf8
username=root
password=root
pom.xml檔案的配置
<?xml version="1.0" encoding="UTF-8"?>
<project xmlns="http://maven.apache.org/POM/4.0.0"
xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/xsd/maven-4.0.0.xsd">
<parent>
<artifactId>myBatis</artifactId>
<groupId>org.example</groupId>
<version>1.0-SNAPSHOT</version>
</parent>
<modelVersion>4.0.0</modelVersion>
<artifactId>myBatis_01</artifactId>
<properties>
<maven.compiler.source>8</maven.compiler.source>
<maven.compiler.target>8</maven.compiler.target>
</properties>
<!--可能出現問題說明:Maven靜態資源過濾問題-->
<build>
<resources>
<resource>
<directory>src/main/java</directory>
<includes>
<include>**/*.xml</include>
</includes>
</resource>
</resources>
</build>
<dependencies>
<!-- https://mvnrepository.com/artifact/log4j/log4j -->
<dependency>
<groupId>log4j</groupId>
<artifactId>log4j</artifactId>
<version>1.2.17</version>
</dependency>
<dependency>
<groupId>org.projectlombok</groupId>
<artifactId>lombok</artifactId>
<version>1.16.10</version>
</dependency>
</dependencies>
</project>
工具類的編寫
public class IDUtil {
public static String genId(){
return UUID.randomUUID().toString().replaceAll("-","");
}
}
package com.xxxx.utils;
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 java.io.IOException;
import java.io.InputStream;
// SqlSessionFactory ---> SqlSession
public class MyBatisUtils {
private static SqlSessionFactory sqlSessionFactory;
static {
try {
// 第一步 : 獲取sqlSessionFactory物件
String resource = "mybatis-config.xml";
InputStream inputStream = Resources.getResourceAsStream(resource);
sqlSessionFactory = new SqlSessionFactoryBuilder().build(inputStream);
} catch (IOException e) {
e.printStackTrace();
}
}
// 既然有了 SqlSessionFactory,顧名思義,我們可以從中獲得 SqlSession 的例項。
// SqlSession 提供了在資料庫執行 SQL 命令所需的所有方法
public static SqlSession getSqlSesion() {
// 自動提交事務
return sqlSessionFactory.openSession(true);
}
}
插入資料(初始化部落格)
Mapper
package com.xxxx.dao;
import com.xxxx.pojo.Blog;
public interface BlogMapper {
int addBlog(Blog blog);
}
Mapper.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.xxxx.dao.BlogMapper">
<insert id="addBlog" parameterType="com.xxxx.pojo.Blog">
insert into blog (id, title, author, create_time, views)
values (#{id},#{title},#{author},#{createTime},#{views});
</insert>
</mapper>
Test
package com.xxxx.dao;
import com.xxxx.pojo.Blog;
import com.xxxx.utils.IDUtil;
import com.xxxx.utils.MyBatisUtils;
import org.apache.ibatis.session.SqlSession;
import org.apache.log4j.Logger;
import org.junit.Test;
import java.util.Date;
public class DaoTest {
//注意導包:org.apache.log4j.Logger
static Logger logger = Logger.getLogger(DaoTest.class);
@Test
public void test(){
try(SqlSession session = MyBatisUtils.getSqlSesion();){
BlogMapper mapper = session.getMapper(BlogMapper.class);
Blog blog = new Blog();
blog.setId(IDUtil.genId());
blog.setTitle("Mybatis如此簡單");
blog.setAuthor("zs");
blog.setCreateTime(new Date());
blog.setViews(9999);
mapper.addBlog(blog);
blog.setId(IDUtil.genId());
blog.setTitle("Java如此簡單");
mapper.addBlog(blog);
blog.setId(IDUtil.genId());
blog.setTitle("Spring如此簡單");
mapper.addBlog(blog);
blog.setId(IDUtil.genId());
blog.setTitle("微服務如此簡單");
mapper.addBlog(blog);
}
}
}
環境搭建完畢!!!
1.2 if
編寫介面類
List<Blog> queryBlogif(Map map);
編寫XML檔案
<select id="queryBlogif" parameterType="map" resultType="com.xxxx.pojo.Blog">
select * from blog where 1=1
<if test="title != null">
and title = #{title}
</if>
<if test="author != null">
and author = #{author}
</if>
</select>
編寫測試
package com.xxxx.dao;
import com.xxxx.pojo.Blog;
import com.xxxx.utils.IDUtil;
import com.xxxx.utils.MyBatisUtils;
import org.apache.ibatis.session.SqlSession;
import org.apache.log4j.Logger;
import org.junit.Test;
import java.util.Date;
import java.util.HashMap;
import java.util.List;
import java.util.Map;
public class DaoTest {
//注意導包:org.apache.log4j.Logger
static Logger logger = Logger.getLogger(DaoTest.class);
@Test
public void test(){
try(SqlSession session = MyBatisUtils.getSqlSesion();){
BlogMapper mapper = session.getMapper(BlogMapper.class);
Map<String, String> map = new HashMap<String, String>();
map.put("title","Mybatis如此簡單");
map.put("author","zs");
List<Blog> blogs = mapper.queryBlogif(map);
for (Blog blog : blogs) {
System.out.println(blog);
}
}
}
}
但是會出現問題
去掉不合規矩的 1=1
<select id="queryBlogif" parameterType="map" resultType="com.xxxx.pojo.Blog">
select * from blog where
<if test="title != null">
and title = #{title}
</if>
<if test="author != null">
and author = #{author}
</if>
</select>
列印一下問題
Preparing: select * from blog where and title = ? and author = ?
用Where解決問題
1.3 Where
<select id="queryBlogif" parameterType="map" resultType="com.xxxx.pojo.Blog">
select * from blog
<where>
<if test="title != null">
title = #{title}
</if>
<if test="author != null">
and author = #{author}
</if>
</where>
</select>
注意我的測試類
public class DaoTest {
//注意導包:org.apache.log4j.Logger
static Logger logger = Logger.getLogger(DaoTest.class);
@Test
public void test(){
try(SqlSession session = MyBatisUtils.getSqlSesion();){
BlogMapper mapper = session.getMapper(BlogMapper.class);
Map<String, String> map = new HashMap<String, String>();
// map.put("title","Mybatis如此簡單");
map.put("author","zs");
List<Blog> blogs = mapper.queryBlogif(map);
for (Blog blog : blogs) {
System.out.println(blog);
}
}
}
}
控制檯列印的sql語句
自動將 and 去掉了
Preparing: select * from blog WHERE author = ?
1.4 choose
有時候,我們不想用到所有的查詢條件,只想選擇其中的一個,查詢條件有一個滿足即可,使用 choose 標籤可以解決此類問題,類似於 Java 的 switch 語句。
編寫介面方法
List<Blog> queryBlogChoose(Map map);
mapper.xml
<select id="queryBlogChoose" parameterType="map" resultType="com.xxxx.pojo.Blog">
select * from blog
<where>
<choose>
<when test="title != null">
title = #{title}
</when>
<when test="author != null">
and author = #{author}
</when>
</choose>
</where>
</select>
測試類
public class DaoTest {
//注意導包:org.apache.log4j.Logger
static Logger logger = Logger.getLogger(DaoTest.class);
@Test
public void test(){
try(SqlSession session = MyBatisUtils.getSqlSesion();){
BlogMapper mapper = session.getMapper(BlogMapper.class);
Map<String, String> map = new HashMap<String, String>();
map.put("title","Mybatis如此簡單");
map.put("author","zs");
List<Blog> blogs = mapper.queryBlogChoose(map);
for (Blog blog : blogs) {
System.out.println(blog);
}
}
}
}
注意列印
map.put("title","Mybatis如此簡單");
map.put("author","zs");
Preparing: select * from blog WHERE title = ?
1.5 Set
編寫介面
int updateBlog(Map map);
mapper.xml
<update id="updateBlog" parameterType="map">
update blog
<set>
<if test="title != null">
title = #{title},
</if>
<if test="author != null">
author = #{author}
</if>
</set>
where id = #{id};
</update>
測試類
public class DaoTest {
//注意導包:org.apache.log4j.Logger
static Logger logger = Logger.getLogger(DaoTest.class);
@Test
public void test(){
try(SqlSession session = MyBatisUtils.getSqlSesion();){
BlogMapper mapper = session.getMapper(BlogMapper.class);
Map<String, String> map = new HashMap<String, String>();
map.put("author","zj");
map.put("id" , "8283887ec6414603972d4a98ce26599d");
mapper.updateBlog(map);
}
}
}
注意列印
update blog SET author = ? where id = ?;
1.6 sql片段
有時候可能某個 sql 語句我們用的特別多,為了增加程式碼的重用性,簡化程式碼,我們需要將這些程式碼抽取出來,然後使用時直接呼叫。
提取SQL片段
<sql id="if">
<if test="title != null">
title = #{title},
</if>
<if test="author != null">
author = #{author}
</if>
</sql>
引用SQL片段
<update id="updateBlog" parameterType="map">
update blog
<set>
<include refid="if"></include>
</set>
where id = #{id};
</update>
注意列印
Parameters: zj(String), 8283887ec6414603972d4a98ce26599d(String)
1.7 Foreach
將資料庫中前三個資料的id修改為1,2,3;
需求:我們需要查詢 blog 表中 id 分別為1,2,3的部落格資訊
編寫介面
List<Blog> queryBlogForeach(Map map);
mapper.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.xxxx.dao.BlogMapper">
<!--
collection:指定輸入物件中的集合屬性
item:每次遍歷生成的物件
open:開始遍歷時的拼接字串
close:結束時拼接的字串
separator:遍歷物件之間需要拼接的字串
select * from blog where 1=1 and (id=1 or id=2 or id=3)
-->
<select id="queryBlogForeach" parameterType="map" resultType="com.xxxx.pojo.Blog">
select * from blog
<where>
<foreach collection="ids" item="id" open="and (" close=")" separator="or">
id=#{id}
</foreach>
</where>
</select>
</mapper>
注意測試類
public class DaoTest {
//注意導包:org.apache.log4j.Logger
static Logger logger = Logger.getLogger(DaoTest.class);
@Test
public void test(){
try(SqlSession session = MyBatisUtils.getSqlSesion();){
BlogMapper mapper = session.getMapper(BlogMapper.class);
Map<String, List> map = new HashMap<>();
List<Integer> ids = new ArrayList<>();
ids.add(1);
ids.add(2);
ids.add(3);
map.put("ids" , ids);
List<Blog> blogs = mapper.queryBlogForeach(map);
for (Blog blog : blogs) {
System.out.println(blog);
}
}
}
}
注意列印
Preparing: select * from blog WHERE ( id=? or id=? or id=? )