MyBatis逆向⼯程的生成过程-编程学习网

一、MyBatis的逆向⼯程

（1）所谓的逆向⼯程是：根据数据库表逆向⽣成Java的pojo类，SqlMapper.xml⽂件，以及Mapper接⼝类等，这真是一个很强大的功能。要完成这个⼯作，需要借助别⼈写好的逆向⼯程插件。

（2）思考：使⽤这个插件的话，需要给这个插件配置哪些信息？

①pojo类名、包名以及⽣成位置。

②SqlMapper.xml⽂件名以及⽣成位置。

③Mapper接⼝名以及⽣成位置。

④连接数据库的信息。

⑤指定哪些表参与逆向⼯程。

......

1.逆向⼯程配置与⽣成

（1）基础环境准备

新建一个普通的Maven模块：mybatis-012-generator

打包⽅式：jar

（2）在pom.xml中添加逆向⼯程插件

①先引入mybatis逆向⼯程的插件，引入仓库中对应的插件坐标。

②允许覆盖：表示原来这些文件存在，true就以覆盖的方式生成文件，false就以追加的方式生成文件。

③引入插件的依赖：我们需要根据数据库表逆向生成pojo类、SqlMapper接口和里面的方法、SqlMapper.xml配置文件等，所以肯定需要mysql的驱动。

<?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">
    <modelVersion>4.0.0</modelVersion>
    <groupId>com.bjpowernode</groupId>
    <artifactId>mybatis-012-generator</artifactId>
    <version>1.0-SNAPSHOT</version>
    <packaging>jar</packaging>
    <!--定制构建过程-->
    <build>
        <!--可配置多个插件-->
        <plugins>
            <!--其中的⼀个插件：mybatis逆向⼯程插件-->
            <plugin>
                <!--插件的GAV坐标-->
                <groupId>org.mybatis.generator</groupId>
                <artifactId>mybatis-generator-maven-plugin</artifactId>
                <version>1.4.1</version>
                <!--允许覆盖-->
                <configuration>
                    <overwrite>true</overwrite>
                </configuration>
                <!--插件的依赖-->
                <dependencies>
                    <!--mysql驱动依赖-->
                    <dependency>
                        <groupId>mysql</groupId>
                        <artifactId>mysql-connector-java</artifactId>
                        <version>5.1.23</version>
                    </dependency>
                </dependencies>
            </plugin>
        </plugins>
    </build>
</project>

（3）配置generatorConfig.xml（基础版）

该⽂件名必须叫做：generatorConfig.xml。

并且该⽂件必须放在类的根路径下。

<?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>
    <!--
        targetRuntime有两个值：
            MyBatis3Simple：生成的是基础版，只有基本的增删改查。
            MyBatis3：生成的是增强版，除了基本的增删改查之外还有复杂的增删改查。
    -->
    <context id="DB2Tables" targetRuntime="MyBatis3Simple">
        <!--防止生成重复代码-->
        <plugin type="org.mybatis.generator.plugins.UnmergeableXmlMappersPlugin"/>
        <commentGenerator>
            <!--是否去掉生成日期-->
            <property name="suppressDate" value="true"/>
            <!--是否去除注释-->
            <property name="suppressAllComments" value="true"/>
        </commentGenerator>
        <!--连接数据库信息-->
        <jdbcConnection driverClass="com.mysql.jdbc.Driver"
                        connectionURL="jdbc:mysql://localhost:3306/mybatis"
                        userId="root"
                        password="123">
        </jdbcConnection>
        <!-- 生成pojo包名和位置 -->
        <javaModelGenerator targetPackage="com.bjpowernode.mybatis.pojo" targetProject="src/main/java">
            <!--是否开启子包-->
            <property name="enableSubPackages" value="true"/>
            <!--是否去除字段名的前后空白-->
            <property name="trimStrings" value="true"/>
        </javaModelGenerator>
        <!-- 生成SQL映射文件的包名和位置 -->
        <sqlMapGenerator targetPackage="com.bjpowernode.mybatis.mapper" targetProject="src/main/resources">
            <!--是否开启子包-->
            <property name="enableSubPackages" value="true"/>
        </sqlMapGenerator>
        <!-- 生成Mapper接口的包名和位置 -->
        <javaClientGenerator
                type="xmlMapper"
                targetPackage="com.bjpowernode.mybatis.mapper"
                targetProject="src/main/java">
            <property name="enableSubPackages" value="true"/>
        </javaClientGenerator>
        <!-- 表名和对应的实体类名-->
        <table tableName="t_car" domainObjectName="Car"/>
    </context>
</generatorConfiguration>

（4）双击运行插件，就可以生成基础版的配置信息

自动生成的CarMapper接口、pojo类Car、CarMapper.xml配置文件

CarMapper接口

package com.bjpowernode.mybatis.mapper;
import com.bjpowernode.mybatis.pojo.Car;
import java.util.List;
public interface CarMapper {
    int deleteByPrimaryKey(Long id);
    int insert(Car row);
    Car selectByPrimaryKey(Long id);
    List<Car> selectAll();
    int updateByPrimaryKey(Car row);
}

pojo类Car

注：生成的pojo类并没有重写toString方法

package com.bjpowernode.mybatis.pojo;
import java.math.BigDecimal;
public class Car {
    private Long id;
    private String carNum;
    private String brand;
    private BigDecimal guidePrice;
    private String produceTime;
    private String carType;
    @Override
    public String toString() {
        return "Car{" +
                "id=" + id +
                ", carNum='" + carNum + '\'' +
                ", brand='" + brand + '\'' +
                ", guidePrice=" + guidePrice +
                ", produceTime='" + produceTime + '\'' +
                ", carType='" + carType + '\'' +
                '}';
    }
    public Long getId() {
        return id;
    }
    public void setId(Long id) {
        this.id = id;
    }
    public String getCarNum() {
        return carNum;
    }
    public void setCarNum(String carNum) {
        this.carNum = carNum == null ? null : carNum.trim();
    }
    public String getBrand() {
        return brand;
    }
    public void setBrand(String brand) {
        this.brand = brand == null ? null : brand.trim();
    }
    public BigDecimal getGuidePrice() {
        return guidePrice;
    }
    public void setGuidePrice(BigDecimal guidePrice) {
        this.guidePrice = guidePrice;
    }
    public String getProduceTime() {
        return produceTime;
    }
    public void setProduceTime(String produceTime) {
        this.produceTime = produceTime == null ? null : produceTime.trim();
    }
    public String getCarType() {
        return carType;
    }
    public void setCarType(String carType) {
        this.carType = carType == null ? null : carType.trim();
    }
}

CarMapper.xml配置文件

<?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.bjpowernode.mybatis.mapper.CarMapper">
  <resultMap id="BaseResultMap" type="com.bjpowernode.mybatis.pojo.Car">
    <id column="id" jdbcType="BIGINT" property="id" />
    <result column="car_num" jdbcType="VARCHAR" property="carNum" />
    <result column="brand" jdbcType="VARCHAR" property="brand" />
    <result column="guide_price" jdbcType="DECIMAL" property="guidePrice" />
    <result column="produce_time" jdbcType="CHAR" property="produceTime" />
    <result column="car_type" jdbcType="VARCHAR" property="carType" />
  </resultMap>
  <delete id="deleteByPrimaryKey" parameterType="java.lang.Long">
    delete from t_car
    where id = #{id,jdbcType=BIGINT}
  </delete>
  <insert id="insert" parameterType="com.bjpowernode.mybatis.pojo.Car">
    insert into t_car (id, car_num, brand, 
      guide_price, produce_time, car_type
      )
    values (#{id,jdbcType=BIGINT}, #{carNum,jdbcType=VARCHAR}, #{brand,jdbcType=VARCHAR}, 
      #{guidePrice,jdbcType=DECIMAL}, #{produceTime,jdbcType=CHAR}, #{carType,jdbcType=VARCHAR}
      )
  </insert>
  <update id="updateByPrimaryKey" parameterType="com.bjpowernode.mybatis.pojo.Car">
    update t_car
    set car_num = #{carNum,jdbcType=VARCHAR},
      brand = #{brand,jdbcType=VARCHAR},
      guide_price = #{guidePrice,jdbcType=DECIMAL},
      produce_time = #{produceTime,jdbcType=CHAR},
      car_type = #{carType,jdbcType=VARCHAR}
    where id = #{id,jdbcType=BIGINT}
  </update>
  <select id="selectByPrimaryKey" parameterType="java.lang.Long" resultMap="BaseResultMap">
    select id, car_num, brand, guide_price, produce_time, car_type
    from t_car
    where id = #{id,jdbcType=BIGINT}
  </select>
  <select id="selectAll" resultMap="BaseResultMap">
    select id, car_num, brand, guide_price, produce_time, car_type
    from t_car
  </select>
</mapper>

2.测试生成的逆向⼯程

（1）环境准备

①依赖：mybatis依赖、mysql驱动依赖、junit依赖、logback依赖

②jdbc.properties、mybatis-config.xml、logback.xml

③拷贝工具类：SqlSessionUtil

（2）编写测试程序（基础版）

package com.bjpowernode.mybatis.test;
import com.bjpowernode.mybatis.mapper.CarMapper;
import com.bjpowernode.mybatis.pojo.Car;
import com.bjpowernode.mybatis.utils.SqlSessionUtil;
import org.apache.ibatis.session.SqlSession;
import org.junit.Test;
import java.util.List;
public class CarMapperTest {
    @Test
    public void testSelectAll(){
        SqlSession sqlSession = SqlSessionUtil.openSession();
        CarMapper mapper = sqlSession.getMapper(CarMapper.class);
        List<Car> cars = mapper.selectAll();
        cars.forEach(car -> System.out.println(car));
        sqlSession.close();
    }
}

执行结果：

（3）配置generatorConfig.xml（增强版）

生成了两个pojo类，并且对于接口中的方法也变多了

CarMapper接口

package com.bjpowernode.mybatis.mapper;
import com.bjpowernode.mybatis.pojo.Car;
import com.bjpowernode.mybatis.pojo.CarExample;
import java.util.List;
import org.apache.ibatis.annotations.Param;
public interface CarMapper {
    long countByExample(CarExample example);
    int deleteByExample(CarExample example);
    int deleteByPrimaryKey(Long id);
    int insert(Car row);
    int insertSelective(Car row);
    List<Car> selectByExample(CarExample example);
    Car selectByPrimaryKey(Long id);
    int updateByExampleSelective(@Param("row") Car row, @Param("example") CarExample example);
    int updateByExample(@Param("row") Car row, @Param("example") CarExample example);
    int updateByPrimaryKeySelective(Car row);
    int updateByPrimaryKey(Car row);
}

pojo类Car

package com.bjpowernode.mybatis.pojo;
import java.math.BigDecimal;
public class Car {
    private Long id;
    private String carNum;
    private String brand;
    private BigDecimal guidePrice;
    private String produceTime;
    private String carType;
    @Override
    public String toString() {
        return "Car{" +
                "id=" + id +
                ", carNum='" + carNum + '\'' +
                ", brand='" + brand + '\'' +
                ", guidePrice=" + guidePrice +
                ", produceTime='" + produceTime + '\'' +
                ", carType='" + carType + '\'' +
                '}';
    }
    public Long getId() {
        return id;
    }
    public void setId(Long id) {
        this.id = id;
    }
    public String getCarNum() {
        return carNum;
    }
    public void setCarNum(String carNum) {
        this.carNum = carNum == null ? null : carNum.trim();
    }
    public String getBrand() {
        return brand;
    }
    public void setBrand(String brand) {
        this.brand = brand == null ? null : brand.trim();
    }
    public BigDecimal getGuidePrice() {
        return guidePrice;
    }
    public void setGuidePrice(BigDecimal guidePrice) {
        this.guidePrice = guidePrice;
    }
    public String getProduceTime() {
        return produceTime;
    }
    public void setProduceTime(String produceTime) {
        this.produceTime = produceTime == null ? null : produceTime.trim();
    }
    public String getCarType() {
        return carType;
    }
    public void setCarType(String carType) {
        this.carType = carType == null ? null : carType.trim();
    }
}

pojo类CarExample：封装查询条件的类

package com.bjpowernode.mybatis.pojo;
import java.math.BigDecimal;
import java.util.ArrayList;
import java.util.List;
public class CarExample {
    protected String orderByClause;
    protected boolean distinct;
    protected List<Criteria> oredCriteria;
    public CarExample() {
        oredCriteria = new ArrayList<>();
    }
    public void setOrderByClause(String orderByClause) {
        this.orderByClause = orderByClause;
    }
    public String getOrderByClause() {
        return orderByClause;
    }
    public void setDistinct(boolean distinct) {
        this.distinct = distinct;
    }
    public boolean isDistinct() {
        return distinct;
    }
    public List<Criteria> getOredCriteria() {
        return oredCriteria;
    }
    public void or(Criteria criteria) {
        oredCriteria.add(criteria);
    }
    public Criteria or() {
        Criteria criteria = createCriteriaInternal();
        oredCriteria.add(criteria);
        return criteria;
    }
    public Criteria createCriteria() {
        Criteria criteria = createCriteriaInternal();
        if (oredCriteria.size() == 0) {
            oredCriteria.add(criteria);
        }
        return criteria;
    }
    protected Criteria createCriteriaInternal() {
        Criteria criteria = new Criteria();
        return criteria;
    }
    public void clear() {
        oredCriteria.clear();
        orderByClause = null;
        distinct = false;
    }
    protected abstract static class GeneratedCriteria {
        protected List<Criterion> criteria;
        protected GeneratedCriteria() {
            super();
            criteria = new ArrayList<>();
        }
        public boolean isValid() {
            return criteria.size() > 0;
        }
        public List<Criterion> getAllCriteria() {
            return criteria;
        }
        public List<Criterion> getCriteria() {
            return criteria;
        }
        protected void addCriterion(String condition) {
            if (condition == null) {
                throw new RuntimeException("Value for condition cannot be null");
            }
            criteria.add(new Criterion(condition));
        }
        protected void addCriterion(String condition, Object value, String property) {
            if (value == null) {
                throw new RuntimeException("Value for " + property + " cannot be null");
            }
            criteria.add(new Criterion(condition, value));
        }
        protected void addCriterion(String condition, Object value1, Object value2, String property) {
            if (value1 == null || value2 == null) {
                throw new RuntimeException("Between values for " + property + " cannot be null");
            }
            criteria.add(new Criterion(condition, value1, value2));
        }
        public Criteria andIdIsNull() {
            addCriterion("id is null");
            return (Criteria) this;
        }
        public Criteria andIdIsNotNull() {
            addCriterion("id is not null");
            return (Criteria) this;
        }
        public Criteria andIdEqualTo(Long value) {
            addCriterion("id =", value, "id");
            return (Criteria) this;
        }
        public Criteria andIdNotEqualTo(Long value) {
            addCriterion("id <>", value, "id");
            return (Criteria) this;
        }
        public Criteria andIdGreaterThan(Long value) {
            addCriterion("id >", value, "id");
            return (Criteria) this;
        }
        public Criteria andIdGreaterThanOrEqualTo(Long value) {
            addCriterion("id >=", value, "id");
            return (Criteria) this;
        }
        public Criteria andIdLessThan(Long value) {
            addCriterion("id <", value, "id");
            return (Criteria) this;
        }
        public Criteria andIdLessThanOrEqualTo(Long value) {
            addCriterion("id <=", value, "id");
            return (Criteria) this;
        }
        public Criteria andIdIn(List<Long> values) {
            addCriterion("id in", values, "id");
            return (Criteria) this;
        }
        public Criteria andIdNotIn(List<Long> values) {
            addCriterion("id not in", values, "id");
            return (Criteria) this;
        }
        public Criteria andIdBetween(Long value1, Long value2) {
            addCriterion("id between", value1, value2, "id");
            return (Criteria) this;
        }
        public Criteria andIdNotBetween(Long value1, Long value2) {
            addCriterion("id not between", value1, value2, "id");
            return (Criteria) this;
        }
        public Criteria andCarNumIsNull() {
            addCriterion("car_num is null");
            return (Criteria) this;
        }
        public Criteria andCarNumIsNotNull() {
            addCriterion("car_num is not null");
            return (Criteria) this;
        }
        public Criteria andCarNumEqualTo(String value) {
            addCriterion("car_num =", value, "carNum");
            return (Criteria) this;
        }
        public Criteria andCarNumNotEqualTo(String value) {
            addCriterion("car_num <>", value, "carNum");
            return (Criteria) this;
        }
        public Criteria andCarNumGreaterThan(String value) {
            addCriterion("car_num >", value, "carNum");
            return (Criteria) this;
        }
        public Criteria andCarNumGreaterThanOrEqualTo(String value) {
            addCriterion("car_num >=", value, "carNum");
            return (Criteria) this;
        }
        public Criteria andCarNumLessThan(String value) {
            addCriterion("car_num <", value, "carNum");
            return (Criteria) this;
        }
        public Criteria andCarNumLessThanOrEqualTo(String value) {
            addCriterion("car_num <=", value, "carNum");
            return (Criteria) this;
        }
        public Criteria andCarNumLike(String value) {
            addCriterion("car_num like", value, "carNum");
            return (Criteria) this;
        }
        public Criteria andCarNumNotLike(String value) {
            addCriterion("car_num not like", value, "carNum");
            return (Criteria) this;
        }
        public Criteria andCarNumIn(List<String> values) {
            addCriterion("car_num in", values, "carNum");
            return (Criteria) this;
        }
        public Criteria andCarNumNotIn(List<String> values) {
            addCriterion("car_num not in", values, "carNum");
            return (Criteria) this;
        }
        public Criteria andCarNumBetween(String value1, String value2) {
            addCriterion("car_num between", value1, value2, "carNum");
            return (Criteria) this;
        }
        public Criteria andCarNumNotBetween(String value1, String value2) {
            addCriterion("car_num not between", value1, value2, "carNum");
            return (Criteria) this;
        }
        public Criteria andBrandIsNull() {
            addCriterion("brand is null");
            return (Criteria) this;
        }
        public Criteria andBrandIsNotNull() {
            addCriterion("brand is not null");
            return (Criteria) this;
        }
        public Criteria andBrandEqualTo(String value) {
            addCriterion("brand =", value, "brand");
            return (Criteria) this;
        }
        public Criteria andBrandNotEqualTo(String value) {
            addCriterion("brand <>", value, "brand");
            return (Criteria) this;
        }
        public Criteria andBrandGreaterThan(String value) {
            addCriterion("brand >", value, "brand");
            return (Criteria) this;
        }
        public Criteria andBrandGreaterThanOrEqualTo(String value) {
            addCriterion("brand >=", value, "brand");
            return (Criteria) this;
        }
        public Criteria andBrandLessThan(String value) {
            addCriterion("brand <", value, "brand");
            return (Criteria) this;
        }
        public Criteria andBrandLessThanOrEqualTo(String value) {
            addCriterion("brand <=", value, "brand");
            return (Criteria) this;
        }
        public Criteria andBrandLike(String value) {
            addCriterion("brand like", value, "brand");
            return (Criteria) this;
        }
        public Criteria andBrandNotLike(String value) {
            addCriterion("brand not like", value, "brand");
            return (Criteria) this;
        }
        public Criteria andBrandIn(List<String> values) {
            addCriterion("brand in", values, "brand");
            return (Criteria) this;
        }
        public Criteria andBrandNotIn(List<String> values) {
            addCriterion("brand not in", values, "brand");
            return (Criteria) this;
        }
        public Criteria andBrandBetween(String value1, String value2) {
            addCriterion("brand between", value1, value2, "brand");
            return (Criteria) this;
        }
        public Criteria andBrandNotBetween(String value1, String value2) {
            addCriterion("brand not between", value1, value2, "brand");
            return (Criteria) this;
        }
        public Criteria andGuidePriceIsNull() {
            addCriterion("guide_price is null");
            return (Criteria) this;
        }
        public Criteria andGuidePriceIsNotNull() {
            addCriterion("guide_price is not null");
            return (Criteria) this;
        }
        public Criteria andGuidePriceEqualTo(BigDecimal value) {
            addCriterion("guide_price =", value, "guidePrice");
            return (Criteria) this;
        }
        public Criteria andGuidePriceNotEqualTo(BigDecimal value) {
            addCriterion("guide_price <>", value, "guidePrice");
            return (Criteria) this;
        }
        public Criteria andGuidePriceGreaterThan(BigDecimal value) {
            addCriterion("guide_price >", value, "guidePrice");
            return (Criteria) this;
        }
        public Criteria andGuidePriceGreaterThanOrEqualTo(BigDecimal value) {
            addCriterion("guide_price >=", value, "guidePrice");
            return (Criteria) this;
        }
        public Criteria andGuidePriceLessThan(BigDecimal value) {
            addCriterion("guide_price <", value, "guidePrice");
            return (Criteria) this;
        }
        public Criteria andGuidePriceLessThanOrEqualTo(BigDecimal value) {
            addCriterion("guide_price <=", value, "guidePrice");
            return (Criteria) this;
        }
        public Criteria andGuidePriceIn(List<BigDecimal> values) {
            addCriterion("guide_price in", values, "guidePrice");
            return (Criteria) this;
        }
        public Criteria andGuidePriceNotIn(List<BigDecimal> values) {
            addCriterion("guide_price not in", values, "guidePrice");
            return (Criteria) this;
        }
        public Criteria andGuidePriceBetween(BigDecimal value1, BigDecimal value2) {
            addCriterion("guide_price between", value1, value2, "guidePrice");
            return (Criteria) this;
        }
        public Criteria andGuidePriceNotBetween(BigDecimal value1, BigDecimal value2) {
            addCriterion("guide_price not between", value1, value2, "guidePrice");
            return (Criteria) this;
        }
        public Criteria andProduceTimeIsNull() {
            addCriterion("produce_time is null");
            return (Criteria) this;
        }
        public Criteria andProduceTimeIsNotNull() {
            addCriterion("produce_time is not null");
            return (Criteria) this;
        }
        public Criteria andProduceTimeEqualTo(String value) {
            addCriterion("produce_time =", value, "produceTime");
            return (Criteria) this;
        }
        public Criteria andProduceTimeNotEqualTo(String value) {
            addCriterion("produce_time <>", value, "produceTime");
            return (Criteria) this;
        }
        public Criteria andProduceTimeGreaterThan(String value) {
            addCriterion("produce_time >", value, "produceTime");
            return (Criteria) this;
        }
        public Criteria andProduceTimeGreaterThanOrEqualTo(String value) {
            addCriterion("produce_time >=", value, "produceTime");
            return (Criteria) this;
        }
        public Criteria andProduceTimeLessThan(String value) {
            addCriterion("produce_time <", value, "produceTime");
            return (Criteria) this;
        }
        public Criteria andProduceTimeLessThanOrEqualTo(String value) {
            addCriterion("produce_time <=", value, "produceTime");
            return (Criteria) this;
        }
        public Criteria andProduceTimeLike(String value) {
            addCriterion("produce_time like", value, "produceTime");
            return (Criteria) this;
        }
        public Criteria andProduceTimeNotLike(String value) {
            addCriterion("produce_time not like", value, "produceTime");
            return (Criteria) this;
        }
        public Criteria andProduceTimeIn(List<String> values) {
            addCriterion("produce_time in", values, "produceTime");
            return (Criteria) this;
        }
        public Criteria andProduceTimeNotIn(List<String> values) {
            addCriterion("produce_time not in", values, "produceTime");
            return (Criteria) this;
        }
        public Criteria andProduceTimeBetween(String value1, String value2) {
            addCriterion("produce_time between", value1, value2, "produceTime");
            return (Criteria) this;
        }
        public Criteria andProduceTimeNotBetween(String value1, String value2) {
            addCriterion("produce_time not between", value1, value2, "produceTime");
            return (Criteria) this;
        }
        public Criteria andCarTypeIsNull() {
            addCriterion("car_type is null");
            return (Criteria) this;
        }
        public Criteria andCarTypeIsNotNull() {
            addCriterion("car_type is not null");
            return (Criteria) this;
        }
        public Criteria andCarTypeEqualTo(String value) {
            addCriterion("car_type =", value, "carType");
            return (Criteria) this;
        }
        public Criteria andCarTypeNotEqualTo(String value) {
            addCriterion("car_type <>", value, "carType");
            return (Criteria) this;
        }
        public Criteria andCarTypeGreaterThan(String value) {
            addCriterion("car_type >", value, "carType");
            return (Criteria) this;
        }
        public Criteria andCarTypeGreaterThanOrEqualTo(String value) {
            addCriterion("car_type >=", value, "carType");
            return (Criteria) this;
        }
        public Criteria andCarTypeLessThan(String value) {
            addCriterion("car_type <", value, "carType");
            return (Criteria) this;
        }
        public Criteria andCarTypeLessThanOrEqualTo(String value) {
            addCriterion("car_type <=", value, "carType");
            return (Criteria) this;
        }
        public Criteria andCarTypeLike(String value) {
            addCriterion("car_type like", value, "carType");
            return (Criteria) this;
        }
        public Criteria andCarTypeNotLike(String value) {
            addCriterion("car_type not like", value, "carType");
            return (Criteria) this;
        }
        public Criteria andCarTypeIn(List<String> values) {
            addCriterion("car_type in", values, "carType");
            return (Criteria) this;
        }
        public Criteria andCarTypeNotIn(List<String> values) {
            addCriterion("car_type not in", values, "carType");
            return (Criteria) this;
        }
        public Criteria andCarTypeBetween(String value1, String value2) {
            addCriterion("car_type between", value1, value2, "carType");
            return (Criteria) this;
        }
        public Criteria andCarTypeNotBetween(String value1, String value2) {
            addCriterion("car_type not between", value1, value2, "carType");
            return (Criteria) this;
        }
    }
    public static class Criteria extends GeneratedCriteria {
        protected Criteria() {
            super();
        }
    }
    public static class Criterion {
        private String condition;
        private Object value;
        private Object secondValue;
        private boolean noValue;
        private boolean singleValue;
        private boolean betweenValue;
        private boolean listValue;
        private String typeHandler;
        public String getCondition() {
            return condition;
        }
        public Object getValue() {
            return value;
        }
        public Object getSecondValue() {
            return secondValue;
        }
        public boolean isNoValue() {
            return noValue;
        }
        public boolean isSingleValue() {
            return singleValue;
        }
        public boolean isBetweenValue() {
            return betweenValue;
        }
        public boolean isListValue() {
            return listValue;
        }
        public String getTypeHandler() {
            return typeHandler;
        }
        protected Criterion(String condition) {
            super();
            this.condition = condition;
            this.typeHandler = null;
            this.noValue = true;
        }
        protected Criterion(String condition, Object value, String typeHandler) {
            super();
            this.condition = condition;
            this.value = value;
            this.typeHandler = typeHandler;
            if (value instanceof List<?>) {
                this.listValue = true;
            } else {
                this.singleValue = true;
            }
        }
        protected Criterion(String condition, Object value) {
            this(condition, value, null);
        }
        protected Criterion(String condition, Object value, Object secondValue, String typeHandler) {
            super();
            this.condition = condition;
            this.value = value;
            this.secondValue = secondValue;
            this.typeHandler = typeHandler;
            this.betweenValue = true;
        }
        protected Criterion(String condition, Object value, Object secondValue) {
            this(condition, value, secondValue, null);
        }
    }
}

CarMapper.xml配置文件

<?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.bjpowernode.mybatis.mapper.CarMapper">
  <resultMap id="BaseResultMap" type="com.bjpowernode.mybatis.pojo.Car">
    <id column="id" jdbcType="BIGINT" property="id" />
    <result column="car_num" jdbcType="VARCHAR" property="carNum" />
    <result column="brand" jdbcType="VARCHAR" property="brand" />
    <result column="guide_price" jdbcType="DECIMAL" property="guidePrice" />
    <result column="produce_time" jdbcType="CHAR" property="produceTime" />
    <result column="car_type" jdbcType="VARCHAR" property="carType" />
  </resultMap>
  <sql id="Example_Where_Clause">
    <where>
      <foreach collection="oredCriteria" item="criteria" separator="or">
        <if test="criteria.valid">
          <trim prefix="(" prefixOverrides="and" suffix=")">
            <foreach collection="criteria.criteria" item="criterion">
              <choose>
                <when test="criterion.noValue">
                  and ${criterion.condition}
                </when>
                <when test="criterion.singleValue">
                  and ${criterion.condition} #{criterion.value}
                </when>
                <when test="criterion.betweenValue">
                  and ${criterion.condition} #{criterion.value} and #{criterion.secondValue}
                </when>
                <when test="criterion.listValue">
                  and ${criterion.condition}
                  <foreach close=")" collection="criterion.value" item="listItem" open="(" separator=",">
                    #{listItem}
                  </foreach>
                </when>
              </choose>
            </foreach>
          </trim>
        </if>
      </foreach>
    </where>
  </sql>
  <sql id="Update_By_Example_Where_Clause">
    <where>
      <foreach collection="example.oredCriteria" item="criteria" separator="or">
        <if test="criteria.valid">
          <trim prefix="(" prefixOverrides="and" suffix=")">
            <foreach collection="criteria.criteria" item="criterion">
              <choose>
                <when test="criterion.noValue">
                  and ${criterion.condition}
                </when>
                <when test="criterion.singleValue">
                  and ${criterion.condition} #{criterion.value}
                </when>
                <when test="criterion.betweenValue">
                  and ${criterion.condition} #{criterion.value} and #{criterion.secondValue}
                </when>
                <when test="criterion.listValue">
                  and ${criterion.condition}
                  <foreach close=")" collection="criterion.value" item="listItem" open="(" separator=",">
                    #{listItem}
                  </foreach>
                </when>
              </choose>
            </foreach>
          </trim>
        </if>
      </foreach>
    </where>
  </sql>
  <sql id="Base_Column_List">
    id, car_num, brand, guide_price, produce_time, car_type
  </sql>
  <select id="selectByExample" parameterType="com.bjpowernode.mybatis.pojo.CarExample" resultMap="BaseResultMap">
    select
    <if test="distinct">
      distinct
    </if>
    <include refid="Base_Column_List" />
    from t_car
    <if test="_parameter != null">
      <include refid="Example_Where_Clause" />
    </if>
    <if test="orderByClause != null">
      order by ${orderByClause}
    </if>
  </select>
  <select id="selectByPrimaryKey" parameterType="java.lang.Long" resultMap="BaseResultMap">
    select 
    <include refid="Base_Column_List" />
    from t_car
    where id = #{id,jdbcType=BIGINT}
  </select>
  <delete id="deleteByPrimaryKey" parameterType="java.lang.Long">
    delete from t_car
    where id = #{id,jdbcType=BIGINT}
  </delete>
  <delete id="deleteByExample" parameterType="com.bjpowernode.mybatis.pojo.CarExample">
    delete from t_car
    <if test="_parameter != null">
      <include refid="Example_Where_Clause" />
    </if>
  </delete>
  <insert id="insert" parameterType="com.bjpowernode.mybatis.pojo.Car">
    insert into t_car (id, car_num, brand, 
      guide_price, produce_time, car_type
      )
    values (#{id,jdbcType=BIGINT}, #{carNum,jdbcType=VARCHAR}, #{brand,jdbcType=VARCHAR}, 
      #{guidePrice,jdbcType=DECIMAL}, #{produceTime,jdbcType=CHAR}, #{carType,jdbcType=VARCHAR}
      )
  </insert>
  <insert id="insertSelective" parameterType="com.bjpowernode.mybatis.pojo.Car">
    insert into t_car
    <trim prefix="(" suffix=")" suffixOverrides=",">
      <if test="id != null">
        id,
      </if>
      <if test="carNum != null">
        car_num,
      </if>
      <if test="brand != null">
        brand,
      </if>
      <if test="guidePrice != null">
        guide_price,
      </if>
      <if test="produceTime != null">
        produce_time,
      </if>
      <if test="carType != null">
        car_type,
      </if>
    </trim>
    <trim prefix="values (" suffix=")" suffixOverrides=",">
      <if test="id != null">
        #{id,jdbcType=BIGINT},
      </if>
      <if test="carNum != null">
        #{carNum,jdbcType=VARCHAR},
      </if>
      <if test="brand != null">
        #{brand,jdbcType=VARCHAR},
      </if>
      <if test="guidePrice != null">
        #{guidePrice,jdbcType=DECIMAL},
      </if>
      <if test="produceTime != null">
        #{produceTime,jdbcType=CHAR},
      </if>
      <if test="carType != null">
        #{carType,jdbcType=VARCHAR},
      </if>
    </trim>
  </insert>
  <select id="countByExample" parameterType="com.bjpowernode.mybatis.pojo.CarExample" resultType="java.lang.Long">
    select count(*) from t_car
    <if test="_parameter != null">
      <include refid="Example_Where_Clause" />
    </if>
  </select>
  <update id="updateByExampleSelective" parameterType="map">
    update t_car
    <set>
      <if test="row.id != null">
        id = #{row.id,jdbcType=BIGINT},
      </if>
      <if test="row.carNum != null">
        car_num = #{row.carNum,jdbcType=VARCHAR},
      </if>
      <if test="row.brand != null">
        brand = #{row.brand,jdbcType=VARCHAR},
      </if>
      <if test="row.guidePrice != null">
        guide_price = #{row.guidePrice,jdbcType=DECIMAL},
      </if>
      <if test="row.produceTime != null">
        produce_time = #{row.produceTime,jdbcType=CHAR},
      </if>
      <if test="row.carType != null">
        car_type = #{row.carType,jdbcType=VARCHAR},
      </if>
    </set>
    <if test="example != null">
      <include refid="Update_By_Example_Where_Clause" />
    </if>
  </update>
  <update id="updateByExample" parameterType="map">
    update t_car
    set id = #{row.id,jdbcType=BIGINT},
      car_num = #{row.carNum,jdbcType=VARCHAR},
      brand = #{row.brand,jdbcType=VARCHAR},
      guide_price = #{row.guidePrice,jdbcType=DECIMAL},
      produce_time = #{row.produceTime,jdbcType=CHAR},
      car_type = #{row.carType,jdbcType=VARCHAR}
    <if test="example != null">
      <include refid="Update_By_Example_Where_Clause" />
    </if>
  </update>
  <update id="updateByPrimaryKeySelective" parameterType="com.bjpowernode.mybatis.pojo.Car">
    update t_car
    <set>
      <if test="carNum != null">
        car_num = #{carNum,jdbcType=VARCHAR},
      </if>
      <if test="brand != null">
        brand = #{brand,jdbcType=VARCHAR},
      </if>
      <if test="guidePrice != null">
        guide_price = #{guidePrice,jdbcType=DECIMAL},
      </if>
      <if test="produceTime != null">
        produce_time = #{produceTime,jdbcType=CHAR},
      </if>
      <if test="carType != null">
        car_type = #{carType,jdbcType=VARCHAR},
      </if>
    </set>
    where id = #{id,jdbcType=BIGINT}
  </update>
  <update id="updateByPrimaryKey" parameterType="com.bjpowernode.mybatis.pojo.Car">
    update t_car
    set car_num = #{carNum,jdbcType=VARCHAR},
      brand = #{brand,jdbcType=VARCHAR},
      guide_price = #{guidePrice,jdbcType=DECIMAL},
      produce_time = #{produceTime,jdbcType=CHAR},
      car_type = #{carType,jdbcType=VARCHAR}
    where id = #{id,jdbcType=BIGINT}
  </update>
</mapper>

（4）编写测试程序（增强版）

（1）增强版的查询方式就比较特殊，特别是根据条件查询，是QBC 风格：Query By Criteria 一种查询方式，比较面向对象，看不到sql语句！

（2）条件查询步骤：

①先封装条件，通过CarExample对象来封装查询条件

②调用carExample.createCriteria()方法来创建查询条件，后面通过" 点. "的方式跟上方法

package com.bjpowernode.mybatis.test;
import com.bjpowernode.mybatis.mapper.CarMapper;
import com.bjpowernode.mybatis.pojo.Car;
import com.bjpowernode.mybatis.pojo.CarExample;
import com.bjpowernode.mybatis.utils.SqlSessionUtil;
import org.apache.ibatis.session.SqlSession;
import org.junit.Test;
import java.math.BigDecimal;
import java.util.List;
public class CarMapperTest {
    @Test
    public void testSelect(){
        SqlSession sqlSession = SqlSessionUtil.openSession();
        CarMapper mapper = sqlSession.getMapper(CarMapper.class);
        // 执行查询
        // 1. 查询一个
        Car car = mapper.selectByPrimaryKey(34L);
        System.out.println(car);
        // 2. 查询所有（selectByExample，根据条件查询，如果条件是null表示没有条件）
        List<Car> cars = mapper.selectByExample(null);
        cars.forEach(car1 -> System.out.println(car1));
        System.out.println("==================");
        // 3.按照条件进行查询
        // QBC 风格：Query By Criteria 一种查询方式，比较面向对象，看不到sql语句。
        // 3.1 封装条件，通过CarExample对象来封装查询条件
        CarExample carExample = new CarExample();
        // 3.2调用carExample.createCriteria()方法来创建查询条件
        carExample.createCriteria().andBrandLike("帕萨特").
                                    andGuidePriceGreaterThan(new BigDecimal(20.0));
        // 添加or
        carExample.or().andCarTypeEqualTo("燃油车");
        // 执行查询
        List<Car> cars1 = mapper.selectByExample(carExample);
        cars1.forEach(car1 -> System.out.println(car1));
        sqlSession.close();
    }
}

以上的SQL语句就等价于：