mybatis入门 - leileigwl

MyBatis#

MyBatis重要核心步骤：省去了建表，写对应的实体类(可以用lombok组件)

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//对应实体类
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public class Account {
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    private long id;
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    private String username;
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    private String password;
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    private int age;
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}

1.创建 MyBatis 的配置文件 config.xml#

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<?xml version="1.0" encoding="UTF-8"?>
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<!DOCTYPE configuration PUBLIC "-//mybatis.org//DTD Config 3.0//EN" "http://mybatis.org/dtd/mybatis-3-config.dtd">
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<configuration>
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    <environments default="account">
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        <environment id="account">
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            <transactionManager type="JDBC"></transactionManager>
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            <dataSource type="POOLED">
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                <property name="driver" value="com.mysql.cj.jdbc.Driver"/>
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                <property name="url" value="jdbc:mysql://localhost:3306/mybatis01?useUnicode=true&characterEncoding=UTF-8"/>
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                <property name="username" value="111"/>
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                <property name="password" value="111"/>
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            </dataSource>
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        </environment>
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    </environments>
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</configuration>

2.通过原生接口实现#

2.1 Mapper.xml的编写#

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<?xml version="1.0" encoding="UTF-8" ?>
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<!DOCTYPE mapper PUBLIC "-//mybatis.org//DTD Mapper 3.0//EN" "http://mybatis.org/dtd/mybatis-3-mapper.dtd">
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<mapper namespace="Account.Account">
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    <insert id="save" parameterType="Account.Account">
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        insert into account (username ,password,age) values (#{username},#{password},#{age});
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    </insert>
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</mapper>

2.2 注册mapper.xml#

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<mappers>
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    <mapper resource="AccountConfig/Mapper.xml"></mapper>
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</mappers>

2.3 调用API#

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public class Test01 {
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    public static void main(String[] args) {
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        InputStream inputStream =Test01.class.getResourceAsStream("/config.xml");
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        SqlSessionFactoryBuilder sqlSessionFactoryBuilder = new SqlSessionFactoryBuilder();
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        SqlSessionFactory build = sqlSessionFactoryBuilder.build(inputStream);
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        SqlSession sqlSession = build.openSession();
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        Account account = new Account(1L,"张三","root",24);
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        String statement ="Account.Account.save";
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        sqlSession.insert(statement,account);
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        sqlSession.commit();
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        sqlSession.close();
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    }
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}

3.自定义接口实现(推荐)#

3.1 编写接口#

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public interface AccountRepository {
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    public int save(Account account);
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    public int update (Account account);
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    public int deleteById(long id);
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    public List<Account> findAll();
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    public Account findById(long id);
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}

3.2 创建对应的xml#

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<?xml version="1.0" encoding="UTF-8" ?>
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<!DOCTYPE mapper PUBLIC "-//mybatis.org//DTD Mapper 3.0//EN" "http://mybatis.org/dtd/mybatis-3-mapper.dtd">
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<mapper namespace="AccountRepository.AccountRepository">
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    <insert id="save" parameterType="Account.Account">
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        insert into account (username, password, age) values (#{username}, #{password}, #{age});
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    </insert>
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    <update id="update" parameterType="Account.Account">
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        update account set username =#{username},password =#{password},age =#{age} where id = #{id};
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    </update>
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    <delete id="deleteById" parameterType="long">
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        delete from account where id = #{id};
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    </delete>
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    <select id="findAll" resultType="Account.Account">
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        select * from account;
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    </select>
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    <select id="findById" resultType="Account.Account">
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        select * from account where id = #{id};
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    </select>
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</mapper>

3.3 调用API#

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public static void main(String[] args) {
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    InputStream resourceAsStream = Test02.class.getClassLoader().getResourceAsStream("config.xml");
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    SqlSessionFactoryBuilder sqlSessionFactoryBuilder = new SqlSessionFactoryBuilder();
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    SqlSessionFactory build = sqlSessionFactoryBuilder.build(resourceAsStream);
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    SqlSession sqlSession = build.openSession();
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    AccountRepository mapper = sqlSession.getMapper(AccountRepository.class);
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    for (Account account : mapper.findAll()) {
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        System.out.println(account);
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    }
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    sqlSession.commit();
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    sqlSession.close();
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}

4.级联查询#

4.1 一对多#

通过学生查班级和学生

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<resultMap id="StudentMap" type="com.Student.Student">
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    <id column="id" property="id"></id>
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    <result column="name" property="name"></result>
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    <association property="classes" javaType="com.Student.Classes">
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        <id column="cid" property="id"></id>
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        <result column="cname" property="name"></result>
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    </association>
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</resultMap>
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<select id="findById" parameterType="long" resultMap="StudentMap">
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    select s.id ,s.name,c.id cid,c.name cname from student s,classes c where s.id = #{id} and c.id =cid;
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</select>

4.2 多对一#

通过班级类查询学生

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<resultMap id="ClassesMap" type="com.Student.Classes">
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    <id column="id" property="id"></id>
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    <result column="name" property="name"></result>
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    <collection property="students" ofType="com.Student.Student">
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        <id column="sid" property="id"></id>
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        <result column="sname" property="name"></result>
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    </collection>
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</resultMap>
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<select id="findById" parameterType="long" resultMap="ClassesMap">
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    select s.id sid,s.name sname,c.id,c.name from student s, classes c where c.id =#{id} and cid =c.id;
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</select>

5.逆向工程#

5.1 导入依赖#

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<dependency>
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    <groupId>org.mybatis.generator</groupId>
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    <artifactId>mybatis-generator-core</artifactId>
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    <version>1.4.0</version>
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</dependency>

5.2 创建配置文件#

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<?xml version="1.0" encoding="UTF-8"?>
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<!DOCTYPE generatorConfiguration
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        PUBLIC "-//mybatis.org//DTD MyBatis Generator Configuration 1.0//EN"
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        "http://mybatis.org/dtd/mybatis-generator-config_1_0.dtd">
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<generatorConfiguration>
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    <context id="testTables" targetRuntime="MyBatis3">
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        <jdbcConnection driverClass="com.mysql.cj.jdbc.Driver"
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                        connectionURL="jdbc:mysql://localhost:3306/mybatis01?useUnicode=true&characterEncoding=UTF-8"
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                        userId="root"
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                        password="root">
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        </jdbcConnection>
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        <javaModelGenerator targetPackage="com.Lei.pojo" targetProject="./src/main/java"></javaModelGenerator>
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        <sqlMapGenerator targetPackage="com.Lei.mapper" targetProject="./src/main/java"></sqlMapGenerator>
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        <javaClientGenerator type="XMLMAPPER" targetPackage="com.Lei.mapper"
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                             targetProject="./src/main/java"></javaClientGenerator>
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        <table tableName="student" domainObjectName="Student"></table>
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    </context>
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</generatorConfiguration>

6.延迟加载#

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<settings>
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    <!-- 打印SQL执行的语句-->
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    <setting name="logImpl" value="STDOUT_LOGGING"/>
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    <!-- 开启延迟加载-->
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    <setting name="lazyLoadingEnabled" value="true"/>
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</settings>

7.MyBatis缓存#

一级缓存：SqlSession 级别，默认开启，不能关闭。
二级缓存：Mapper 级别，默认关闭，可以开启。

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<settings>
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    <!-- 开启二级缓存 -->
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    <setting name="cacheEnabled" value="true"/>
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</settings>

8.动态SQL#

标签名	作用
if	根据表达式的结果来决定是否将对应的语句添加到 SQL 中
where	自动判断是否要删除语句块中的 and 关键字
choose when	类似于if和where的连用
trim	自动删除语句前后的指定值
set	用于 update 操作，会自动根据参数选择生成 SQL 语句
foreach	迭代生成一系列值，主要用于 SQL 的 in 语句

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<select id="findByAccount" resultType="com.Account.Account" parameterType="com.Account.Account">
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    select *from account
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    <where>
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        <if test="id!=0"> and id= #{id}</if>
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        <if test="username!=null"> and username = #{username}</if>
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        <if test="password"> and password = #{password}</if>
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        <if test="age!=0"> and age = #{age}</if>
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    </where>
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</select>