Data Access 之 MyBatis（七）- MBG & PageHelper

RiemannHypothesis

发布于 2022-08-19 17:13:07

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发布于 2022-08-19 17:13:07

文章被收录于专栏：Elixir

一、MyBatis Generator

MyBatis逆向工程是指可以根据数据库表的分析逆向生成Entity实体类、Mapper接口以及Mapper XML等类和XML文件，逆向工程会用到MyBatis官方提供的代码生成器即MyBatis Generator

1.1 工程搭建

新建项目mybatis-mbg-pagehelper，项目依赖与QA 由浅入深持久层框架（七）- MyBatis Cache中的mybatis-cache项目的依赖一致，这里不再重复。但是需要新增加如上所述的Mybatis Generator Core的依赖

<!-- https://mvnrepository.com/artifact/org.mybatis.generator/mybatis-generator-core -->
<dependency>
    <groupId>org.mybatis.generator</groupId>
    <artifactId>mybatis-generator-core</artifactId>
    <version>1.4.0</version>
</dependency>

MyBatis Generator XML Configuration File 示例，拷贝内容放到resource目录下的generatorConfig.xml文件中。

主要修改

数据库连接信息配置
生成的Entity实体类位置配置
生成的Mapper XML文件存放位置配置
生成的Mapper接口位置配置
映射的Table配置 `xml

<context id="test" targetRuntime="MyBatis3" >
    <!--修改数据库连接配置-->
    <jdbcConnection driverClass="com.mysql.cj.jdbc.Driver"
                    connectionURL="jdbc:mysql://localhost:3306/test?useUnicode=true&amp;amp;characterEncoding=utf8&amp;amp;autoReconnect=true&amp;amp;useSSL=false&amp;amp;serverTimezone=Asia/Shanghai"
                    userId="root"
                    password="root">
    </jdbcConnection>

    <javaTypeResolver >
        <property name="forceBigDecimals" value="false" />
    </javaTypeResolver>

    <!--生成Java Model即Entity实体类-->
    <javaModelGenerator targetPackage="com.citi.entity" targetProject="./src/main/java">
        <property name="enableSubPackages" value="true" />
        <property name="trimStrings" value="true" />
    </javaModelGenerator>

    <!--SQL XML映射文件生成器-->
    <sqlMapGenerator targetPackage="mappers"  targetProject="./src/main/resources">
        <property name="enableSubPackages" value="true" />
    </sqlMapGenerator>

    <!--生成Mapper接口-->
    <javaClientGenerator type="XMLMAPPER" targetPackage="com.citi.mapper"  targetProject="./src/main/java">
        <property name="enableSubPackages" value="true" />
    </javaClientGenerator>

    <!--生成器所用到的表，配置生成的实体类名-->
    <table schema="test" tableName="t_cat" domainObjectName="Cat" >
        <!--<property name="useActualColumnNames" value="true"/>-->
        <!--<generatedKey column="ID" sqlStatement="DB2" identity="true" />-->
        <!--<columnOverride column="DATE_FIELD" property="startDate" />-->
        <!--<ignoreColumn column="FRED" />-->
        <!--<columnOverride column="LONG_VARCHAR_FIELD" jdbcType="VARCHAR" />-->
    </table>

    <table schema="test" tableName="t_employee" domainObjectName="Employee" >
    </table>
    <table schema="test" tableName="t_teacher" domainObjectName="Teacher" >
    </table>

</context>

运行方式主要有三种，第一种是通过命令行的方式生成代码

java -jar mybatis-generator-core-x.x.x.jar -configfile \temp\generatorConfig.xml -overwrite

第二种方式是在test包下新增测试代码，通过执行Java代码生成代码

public class MyBatisGenerator {

    public static void main(String[] args) throws Exception {
        List<String> warnings = new ArrayList<String>();
        boolean overwrite = true;
        File configFile = new File("generatorConfig.xml");
        ConfigurationParser cp = new ConfigurationParser(warnings);
        Configuration config = cp.parseConfiguration(configFile);
        DefaultShellCallback callback = new DefaultShellCallback(overwrite);
        MyBatisGenerator myBatisGenerator = new MyBatisGenerator(config,
                callback, warnings);
        //代码生成
        myBatisGenerator.generate(null);
        System.out.println("代码生成器运行结束");
    }

}

第三种方式是通过通过Maven插件的方式生成代码，在pom.xml中增加build配置

<build>
    <finalName>mybatis-mbg-pagehelper</finalName>
    <plugins>
        <plugin>
            <groupId>org.apache.maven.plugins</groupId>
            <artifactId>maven-compiler-plugin</artifactId>
            <version>3.8.1</version>
            <configuration>
                <source>1.8</source>
                <target>1.8</target>
                <encoding>UTF-8</encoding>
            </configuration>
        </plugin>

        <plugin>
            <groupId>org.mybatis.generator</groupId>
            <artifactId>mybatis-generator-maven-plugin</artifactId>
            <version>1.4.0</version>
            <configuration>
                <!--是否覆盖原有代码-->
                <overwrite>true</overwrite>
                <verbose>true</verbose>
            </configuration>
            <dependencies>
                <dependency>
                    <groupId>mysql</groupId>
                    <artifactId>mysql-connector-java</artifactId>
                    <version>8.0.16</version>
                </dependency>
            </dependencies>
        </plugin>
    </plugins>
</build>

打开右侧侧边栏的Maven目录下的Plugins，多出一个mybatis-generator插件

双击该插件即可生成代码

控制台输出BUILD SUCCESS，说明已经成功生成了Mapper接口、Mapper映射文件以及Entity实体类代码

可以看出entity包中除了实体类还有XXXEXample类，这是用来封装查询条件的实体类，MyBatis除了生成简单的CRUD代码，还生成了复杂查询的代码，mapper包中的Mapper接口封装复杂查询的方法，mappers目录下的Mapper XML文件中也实现了复杂查询的SQL语句。

当然，MyBatis也支持生成只有简单的CRUD代码，只需要讲generatorConfig.xml文件中context标签的属性更改一下就可以

<context id="test" targetRuntime="MyBatis3Simple" >
<!--中间内容无变化-->
</context>

在context标签增加新的标签，去除自动生成的注释

<commentGenerator>
    <!-- 是否去除自动生成的注释 true：是 ： false:否 -->
    <property name="suppressAllComments" value="true"/>
</commentGenerator>

1.2 测试

在test包下新建TeacherMapperTest类

public class TeacherMapperTest {

    SqlSessionFactory sqlSessionFactory = null;
    SqlSession openSession = null;

    @Before
    public void setUp() throws Exception {
        String resource = "mybatis-config.xml";
        InputStream inputStream = Resources.getResourceAsStream(resource);
        sqlSessionFactory = new SqlSessionFactoryBuilder().build(inputStream);
        openSession = sqlSessionFactory.openSession();
    }

    @After
    public void tearDown(){
        openSession.close();
    }
    
    @Test
    public void selectByExample() {
        TeacherMapper teacherMapper = openSession.getMapper(TeacherMapper.class);
        TeacherExample example = new TeacherExample();
        example.setOrderByClause("id DESC");
        TeacherExample.Criteria criteria = example.createCriteria();
        criteria.andClassNameLike("三年%");
        List<Teacher> teachers = teacherMapper.selectByExample(example);
        for (Teacher teacher : teachers) {
            System.out.println(teacher.getId());
        }
    }
}

TeacherExample是用来构造查询条件的实体类，可以用来设置SQL语句中的order by、distinct、or等关键字。而where后面的查询条件如：class_name like '%三年%'或者 id between 2,3 或者大于小于等都需要通过TeacherExample调用createCriteria()方法生成一个Criteria类，然后设置查询条件

执行该测试方法

控制它打印出的SQL语句，实现了条件查询

二、PageHelper

快速进行分页的插件

1. 引入分页插件

在 pom.xml 中添加如下依赖：

<!-- https://mvnrepository.com/artifact/com.github.pagehelper/pagehelper -->
<dependency>
    <groupId>com.github.pagehelper</groupId>
    <artifactId>pagehelper</artifactId>
    <version>5.3.0</version>
</dependency>

2. 配置拦截器插件

1. 在 MyBatis 配置 xml 中配置拦截器插件

<!--
plugins在配置文件中的位置必须符合要求，否则会报错，顺序如下:
properties?, settings?,
typeAliases?, typeHandlers?,
objectFactory?,objectWrapperFactory?,
plugins?,
environments?, databaseIdProvider?, mappers?
-->
<plugins>
    <!-- com.github.pagehelper为PageHelper类所在包名 -->
    <plugin interceptor="com.github.pagehelper.PageInterceptor">
        <!-- 使用下面的方式配置参数，后面会有所有的参数介绍 -->
        <property name="param1" value="value1"/>
    </plugin>
</plugins>

TeacherMapper中新增方法insertBatch，批量插入数据用于分页

int insertBatch(@Param("teacherList") List<Teacher> teacherList);

在TeacherMapper.xml中增加SQL 映射语句

<insert id="insertBatch">
  INSERT INTO t_teacher(teacher_name, class_name, address, birth_date)
  VALUES
  <foreach collection="teacherList" separator="," item="teacher">
      (#{teacher.teacherName}, #{teacher.className}, #{teacher.address}, #{teacher.birthDate})
  </foreach>
</insert>

在TeacherMapperTest中增加测试方法

@Test
public void insertBatch(){
    TeacherMapper teacherMapper = openSession.getMapper(TeacherMapper.class);
    List<Teacher> teacherList = new ArrayList<>();
    for (int i = 0; i < 51; i++) {
        Teacher teacher = new Teacher();
        teacher.setTeacherName("Mark " + i);
        teacher.setClassName("三年" + i+ "班");
        teacher.setAddress("New York");
        teacher.setBirthDate(new Date());
        teacherList.add(teacher);
    }
    teacherMapper.insertBatch(teacherList);
    openSession.commit();
}

执行该测试，往数据库中插入50条数据

TeacherMapper接口中新增方法，获取所有的Teacher，对查询结果使用分页

List<Teacher> getAllTeachers();

在TeacherMapper.xml中增加SQL映射

<select id="getAllTeachers" resultType="com.citi.entity.Teacher">
  select * from t_teacher
</select>

在test包下的TeacherMapperTest中增加测试方法

@Test
public void getAllTeachers(){
    TeacherMapper teacherMapper = openSession.getMapper(TeacherMapper.class);
    // 紧跟着PageHelp的查询是分页查询，其他的就是查询全部
    PageHelper.startPage(4,5);
    List<Teacher> teacherList = teacherMapper.getAllTeachers();


    // 将查询的结果使用pageInfo封装
    PageInfo<Teacher> pageInfo = new PageInfo<>(teacherList);
    System.out.println("当前页码为:" + pageInfo.getPageNum());
    System.out.println("总页码数:" + pageInfo.getPages());
    System.out.println("总记录数:" + pageInfo.getTotal());
    System.out.println("当前页面记录数:" + pageInfo.getSize());
    System.out.println("上一页:" + pageInfo.getPrePage());
    System.out.println("下一页:" + pageInfo.getNextPage());
}

执行测试