MyBatis 注解开发+逆向(Generator)

注解开发

最初设计时，MyBatis 是一个 XML 驱动的框架。配置信息是基于 XML 的，而且映射语句也是定义在 XML 中的。随着技术的更新发展,对于开发效率要求也原来越高,特别是一些小型项目;越来越多的框架开始支持注解,

到MyBatis3时,MyBatis对注解有了完善的支持,利用注解可以在一些情况下提高开发效率

但不幸的是，Java 注解的的表达力和灵活性十分有限。尽管很多时间都花在调查、设计和试验上， 最强大的 MyBatis 映射并不能用注解来构建

1. select

接口方法声明:

import com.yyh.pojo.User;
import org.apache.ibatis.annotations.Select;

public interface UserMapper2 {
    @Select("select * from kuser where id = #{id}")
    public User selectUserByID(int id);
}

测试方法:

@Test
public void selectTest(){
    SqlSession session = factory.openSession();
    UserMapper2 mapper = session.getMapper(UserMapper2.class);
    User user = mapper.selectUserByID(2);
    System.out.println(user);
    session.close();
}

不要忘记注册这个接口到全局配置中

<mappers>
	<mapper class="com.yyh.mapper.UserMapper2"/>
</mappers>

2. sql语句多个参数

接口方法声明:

@Select("select * from kuser where sex = #{sex} and name like '%${name}%'")
public List<User> selectUserBySexAndName(@Param("sex") String sex, @Param("name") String name);

测试方法:

@Test
public void selectTest2(){
    SqlSession session = factory.openSession();
    UserMapper2 mapper = session.getMapper(UserMapper2.class);
    List<User> users = mapper.selectUserBySexAndName("1","张");
    System.out.println(users);
    session.close();
}

当sql语句需要多个参数时则必须将多个参数打包到一个对象中,通常是POJO或Map,上面的案例中使用了@Param注解本质就是告诉MyBatis有多个参数MyBatis会自动创建一个Map,然后将@Param的值作为Key,然后将Map传给sql,你也可以手动传一个Map

接口方法声明:

@Select("select * from kuser where sex = #{sex} and name like '%${name}%'")
public List<User> selectUserBySexAndName(Map<String,Object> params);

测试方法:

@Test
public void selectTest2(){
    SqlSession session = factory.openSession();
    UserMapper2 mapper = session.getMapper(UserMapper2.class);
    Map<String,Object> params = new HashMap<>(); //存储参数的Map
    params.put("sex","1");
    params.put("name","张");
    List<User> users = mapper.selectUserBySexAndName(params);
    System.out.println(users);
    session.close();
}

3. insert

接口方法声明:

@Insert("insert into kuser values(null,#{name},#{birthday},#{sex},#{address})")
public int insertUser(User user);

测试方法:

@Test
public void insertTest() {
    SqlSession session = factory.openSession();
    UserMapper2 mapper = session.getMapper(UserMapper2.class);
    
    User user = new User();
    user.setName("jerry");
    user.setSex("1");
    user.setAddress("亚洲中国");
    user.setBirthday(new Date());
    
    mapper.insertUser(user);
    session.commit();
    session.close();
}

获取自增主键

在@select注解的下方添加@selectKey注解来完成对自增主键的获取

@Insert("insert into kuser values(null,#{name},#{birthday},#{sex},#{address})")
@SelectKey(statement = "select last_insert_id()",keyProperty = "id",resultType = Integer.class,before = false)
public int insertUser(User user);

在执行insert之后执行last_insert_id()函数获取自增值,然后放入对象的某个属性中;

4. update

接口方法声明:

@Update("update kuser set name = #{name}, birthday = #{birthday}, sex = #{sex}, address = #{address} where id = #{id}")
public int updateUser(User u);
// 如果一行太长可以换行些 但是要注意sql语法

测试方法:

@Test
public void updateTest() {
    SqlSession session = factory.openSession();
    UserMapper2 mapper = session.getMapper(UserMapper2.class);

    User user = mapper.selectUserByID(1);
    user.setName("王六子");

    mapper.updateUser(user);
    session.commit();
    session.close();
}

5.delete

接口方法声明:

@Delete("delete from kuser where id = #{id}")
public int deleteUserByID(int id);

测试方法:

@Test
public void deleteTest() {
    SqlSession session = factory.openSession();
    UserMapper2 mapper = session.getMapper(UserMapper2.class);
    mapper.deleteUserByID(12);
    session.commit();
    session.close();
}

6. 动态sql

动态sql指语句中包含逻辑代码,需要先运行逻辑代码,最后产生sql语句,所以需要在注解中告诉MyBatis这是一个动态sql,通过<script>sql....</script>语法来指定;

若想要在sql中使用各种标签则必须添加上述根标签,否则MyBatis会将整体作为sql语句

接口方法声明:

@Select("<script>" +
            "select * from kuser" +
            "<where>" +
                "<if test='name != null'>" +
                    "and name like '%${name}%'" +
                "</if>" +
                "<if test='sex != null'>" +
                    "and sex = #{sex}" +
                "</if>" +
            "</where>" +
        "</script>")
public List<User> searchUserByNameAndSex(@Param("name") String name,@Param("sex") String sex);

测试代码:

 @Test
    public void dynamicSqlTest(){
        SqlSession session = factory.openSession();
        UserMapper2 mapper = session.getMapper(UserMapper2.class);
        List<User> users = mapper.searchUserByNameAndSex(null,null);
//        List<User> users = mapper.searchUserByNameAndSex("张",null);
//        List<User> users = mapper.searchUserByNameAndSex("张", "2");
        System.out.println(users);
        session.close();
    }

7.结果映射(ResultMap)

1.自定义字段与属性对应关系

准备工作:将数据库中的name字段修改为username,然后我们通过ResultMap来手动映射name字段

接口方法声明:

@Select("select *from kuser where username = #{name}")
@Results({
        @Result(id = true,column = "id",property = "id"),
        @Result(column = "username",property = "name"),
})
public User selectUserByName(String name);

测试代码省略..

重复使用Results

可以发现,MyBatis默认会自动映射所有字段和属性匹配的数据,另外id表示是否为主键字段,默认为false

强调:Results可以位于对应方法的上面或下面,但是无法跨域其他方法,默认只对当前方法有效,如果需要重复使用则需要为其指定id

接口方法声明:

//定义
@Results(id="map1",value = {
        @Result(id = true,column = "id",property = "id"),
        @Result(column = "username",property = "name"),
})
//.....中间必须间隔其他方法不能立即应用到某个ResultMap

使用:

@Select("select *from kuser where username = #{name}")
//通过@ResultMap注解 并传入id来使用
@ResultMap("map1")
public User selectUserByName(String name);

注意:
@Results的定义不能和使用它的@ResultMap一起出现,既然是重复使用的,建议统一放在接口的最上面,
如果是当前要使用的并且要重用,直接使用Results即可,不需要在下面添加ResultMap就像下面这样:

@Select("select *from kuser where username = #{name}")
@Results(id="map1",value = {
        @Result(id = true,column = "id",property = "id"),
        @Result(column = "username",property = "name"),
})
public User selectUserByName(String name);

2.关联查询

一对多关联

//实现根据用户姓名查询用户信息和订单信息
@Select("select *from kuser where username = #{name}")
@Results(value = {
        @Result(id = true,column = "id",property = "id"),
        @Result(column = "username",property = "name"),
        //一对多关联,指定子查询语句的方法名称(全限定名称)column指定传给子查询的参数
        @Result(column = "id",property = "orders",many = @Many(select = "com.yyh.mapper.UserMapper2.selectOrdersByID")),
})
public User selectUserAdnOrdersByUserName(String name);


//注意这里的条件字段时order表中的字段
@Select("select *from Orders where user_id = #{id}")
public List<Order> selectOrdersByID(int id);

一对一关联 只需要修改属性名称和注解名称即可:

 @Select("select *from orders where id = #{id}")
    @Results(value = {
            @Result(id = true,column = "id",property = "id"),
            @Result(column = "user_id",property = "user" ,one = @One(select = "com.yyh.mapper.UserMapper2.selectUserByID")),
    })
    public Order selectOrderByID(int id);

逆向工程(generator)

generator翻译为生成器,是MyBatis开源的一个插件,可以从数据库获取表信息,自动生成Mapper.xml,POJO,以及Mapper接口

但问题是,MyBatis不可能完全清楚我们的业务需求,所以其自动生成的sql只能满足基本的CRUD操作,而无法帮助我们进行连表操作,(当然包括带有条件的CRUD)

使用步骤

1.使用Maven添加generator插件

<build>
    <plugins>
      <plugin>
      	<groupId>org.mybatis.generator</groupId>
        <artifactId>mybatis-generator-maven-plugin</artifactId>
        <version>1.3.7</version>
	      <configuration>
          			<!-- 是否覆盖已存在的接口和POJO该配置不包括Mapper  
									若为False将会生成版本记录-->
                <overwrite>true</overwrite>
        </configuration>
        </plugin>
    </plugins>
</build>

2.创建数据库配置文件,位于resource下名为jdbc.properties

driver = com.mysql.jdbc.Driver
url = jdbc:mysql:///HMDB?serverTimezone=Asia/Shanghai&characterEncoding=utf8&useSSL=false
user = root
password = admin
location = /Users/jerry/.m2/repository/mysql/mysql-connector-java/5.1.44/mysql-connector-java-5.1.44.jar

3.创建配置文件,位于resource下名为generatorConfig.xml

<?xml version="1.0" encoding="UTF-8"?> <!DOCTYPE generatorConfiguration
        PUBLIC "-//mybatis.org//DTD MyBatis Generator Configuration 1.0//EN"
        "http://mybatis.org/dtd/mybatis-generator-config_1_0.dtd">
<generatorConfiguration>
    <!--导入属性配置-->
    <properties resource="jdbc.properties"></properties>
    <!--指定特定数据库的jdbc驱动jar包的位置-->
    <classPathEntry location="${location}"/>
    <context id="default" targetRuntime="MyBatis3">
        <!-- optional，旨在创建class时，对注释进行控制 -->
        <commentGenerator>
            <property name="suppressDate" value="true"/>
            <property name="suppressAllComments" value="true"/>
        </commentGenerator>

        <!--jdbc的数据库连接 -->
        <jdbcConnection
                driverClass="${driver}" connectionURL="${url}" userId="${user}" password="${password}">
        </jdbcConnection>

        <!-- 非必需，类型处理器，在数据库类型和java类型之间的转换控制-->
        <javaTypeResolver>
            <property name="forceBigDecimals" value="false"/>
        </javaTypeResolver>

        <!--Model模型生成器,用来生成含有主键key的类，记录类 以及查询Example类
        targetPackage 指定生成的model生成所在的包名
        targetProject 指定在该项目下所在的路径 -->
        <javaModelGenerator targetPackage="com.yyh.pojo" targetProject="src/main/java">
            <!-- 是否允许子包，即targetPackage.schemaName.tableName -->
            <property name="enableSubPackages" value="false"/>
            <!-- 是否对model添加 构造函数 -->
            <property name="constructorBased" value="true"/>
            <!-- 是否对类CHAR类型的列的数据进行trim操作 -->
            <property name="trimStrings" value="true"/>
            <!-- 建立的Model对象是否 不可改变 即生成的Model对象不会有 setter方法，只有构造方法 -->
            <property name="immutable" value="false"/>
         </javaModelGenerator>

        <!--mapper映射文件生成所在的目录 为每一个数据库的表生成对应的SqlMap文件 -->
        <sqlMapGenerator targetPackage="com.yyh.dao"
                         targetProject="src/main/resources">
            <property name="enableSubPackages" value="false"/>
        </sqlMapGenerator>

        <!--mapper接口文件生成所在的目录 为每一个数据库的表生成对应的接口文件 -->
        <javaClientGenerator type="XMLMAPPER" targetPackage="com.yyh.dao" targetProject="src/main/java">
            <!-- enableSubPackages:是否让schema(数据库名称)作为包的后缀 -->
            <property name="enableSubPackages" value="false"/>
        </javaClientGenerator>


        <!--指定需要生成的表-->
        <table  tableName="category"></table>
        <table  tableName="orders"></table>
        <table  tableName="products"></table>
        <table  tableName="kuser"></table>
    </context>
</generatorConfiguration>

若自定义配置文件名称则需要在pom中指定

<build>
    <plugins>
        <plugin>
            <groupId>org.mybatis.generator</groupId>
            <artifactId>mybatis-generator-maven-plugin</artifactId>
            <version>1.3.7</version>
            <configuration>
              	<!-- 自定义配置文件 相对于项目根目录-->
                <configurationFile>src/main/resources/aaaa.xml</configurationFile>
                <overwrite>true</overwrite>
            </configuration>
        </plugin>
    </plugins>
</build>

3.运行generator

可在idea右侧的maven菜单中双击执行mybatis-generator:generate

也可利用maven命令执行:mybatis-generator:generate

4.条件查询的使用查看POJO包,会发现每个POJO对应了一个Example,这是什么呢?

generator的目标是尽可能的帮我们减少sql的编写,如果只能进行简单的CRUD那意义不大,于是generator使用了一套Example来帮助我们用OOP(面向对象)的方式来完成SQL中的条件拼接

其设计思想是将条件看做是一个对象,该对象包含了SQL中常见的比较,逻辑运算等......打开文件你会发现其本质就是帮我们拼接响应的sql符号和关键字

5.CRUD案例

import com.yyh.dao.KuserMapper;
import com.yyh.pojo.Kuser;
import com.yyh.pojo.KuserExample;
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.Before;
import org.junit.Test;

import java.io.IOException;
import java.io.InputStream;
import java.util.List;

public class GeneratorTest {
    private SqlSessionFactory factory;

    @Before
    public void init() throws IOException {
        //获取的工厂构造器
        SqlSessionFactoryBuilder builder = new SqlSessionFactoryBuilder();
        //加载配置文件
        InputStream stream = Resources.getResourceAsStream("mybatis-config.xml");
        //获得会话工厂
        factory = builder.build(stream);
    }
    //查询
    @Test
    public void test(){
        SqlSession session = factory.openSession();
        KuserMapper mapper = session.getMapper(KuserMapper.class);
        Kuser kuser = mapper.selectByPrimaryKey(1);
        System.out.println(kuser.getSex());
        System.out.println(kuser.getAddress());
        System.out.println(kuser.getBirthday());
        System.out.println(kuser.getUsername());
    }
    //修改
    @Test
    public void test2(){
        SqlSession session = factory.openSession();
        KuserMapper mapper = session.getMapper(KuserMapper.class);
        Kuser kuser = mapper.selectByPrimaryKey(1);
        kuser.setUsername("XXXXXXXXX");
        mapper.updateByPrimaryKey(kuser);
        session.commit();
    }
    //添加
    @Test
    public void test3(){
        SqlSession session = factory.openSession();
        KuserMapper mapper = session.getMapper(KuserMapper.class);
        Kuser auser = new Kuser();
        auser.setUsername("jack");
        auser.setAddress("北京东城");
        mapper.insert(auser);
        session.commit();
        }

    //删除
    @Test
    public void test4() {
        SqlSession session = factory.openSession();
        KuserMapper mapper = session.getMapper(KuserMapper.class);
        mapper.deleteByPrimaryKey(13);
        session.commit();
    }
    //and条件
    @Test
    public void test5() {
        SqlSession session = factory.openSession();
        KuserMapper mapper = session.getMapper(KuserMapper.class);
        KuserExample kuserExample = new KuserExample();

        KuserExample.Criteria criteria = kuserExample.createCriteria();
        criteria.andBirthdayIsNotNull();
        criteria.andUsernameLike("%张%");

        List<Kuser> kusers = mapper.selectByExample(kuserExample);
        System.out.println(kusers);
    }
    // or条件
    @Test
    public void test6() {
        SqlSession session = factory.openSession();
        KuserMapper mapper = session.getMapper(KuserMapper.class);
        KuserExample kuserExample = new KuserExample();
        //创建一个条件对象,可以包含n个and
        KuserExample.Criteria criteria1 = kuserExample.createCriteria();
        criteria1.andUsernameLike("%张%");
        //创建一个条件对象可以包含n个and,且前面添加or关键字
        KuserExample.Criteria criteria2 = kuserExample.or();
        criteria2.andBirthdayIsNull();
        //最终的意思是 名字带有张的 或者生日为空的;  具体查看生产的sql即可
      
        List<Kuser> kusers = mapper.selectByExample(kuserExample);
        System.out.println(kusers);
    }  
}

注意:重新生成的Mapper文件时不会不会覆盖之前的Mapper,而是会直接在里面添加sql导致id冲突,所以重新生成mapper时一定要手动删除已存在的mapper