【MyBatis】| MyBatis的逆向⼯程

小灰灰 2024-03-30 16:16 33阅读 0赞

**目录**

一：MyBatis的逆向⼯程

1. 逆向⼯程配置与⽣成

2. 测试生成的逆向⼯程

--------------------

## 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>
    
        
        <build>
            
            <plugins>
                
                <plugin>
                    
                    <groupId>org.mybatis.generator</groupId>
                    <artifactId>mybatis-generator-maven-plugin</artifactId>
                    <version>1.4.1</version>
                    
                    <configuration>
                        <overwrite>true</overwrite>
                    </configuration>
                    
                    <dependencies>
                        
                        <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）

> **①该⽂件名必须叫做：generatorConfig.xml！**
> 
> **②并且该⽂件必须放在类的根路径下（src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>
        
        <context id="DB2Tables" targetRuntime="MyBatis3Simple">
            
            <plugin type="org.mybatis.generator.plugins.UnmergeableXmlMappersPlugin"/>
    
            <commentGenerator>
                
                <property name="suppressDate" value="true"/>
                
                <property name="suppressAllComments" value="true"/>
            </commentGenerator>
    
            
            <jdbcConnection driverClass="com.mysql.jdbc.Driver"
                            connectionURL="jdbc:mysql://localhost:3306/mybatis"
                            userId="root"
                            password="***">
            </jdbcConnection>
    
            
            <javaModelGenerator targetPackage="com.bjpowernode.mybatis.pojo" targetProject="src/main/java">
                
                <property name="enableSubPackages" value="true"/>
                
                <property name="trimStrings" value="true"/>
            </javaModelGenerator>
    
            
            <sqlMapGenerator targetPackage="com.bjpowernode.mybatis.mapper" targetProject="src/main/resources">
                
                <property name="enableSubPackages" value="true"/>
            </sqlMapGenerator>
    
            
            <javaClientGenerator
                    type="xmlMapper"
                    targetPackage="com.bjpowernode.mybatis.mapper"
                    targetProject="src/main/java">
                <property name="enableSubPackages" value="true"/>
            </javaClientGenerator>
    
            
            <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

![f55a2c81fb3149929759c34b9ecefe0d.png][]

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

![8c30980efccb4733908483ea67a34027.png][]

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，需要自己手动加上！**

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

#### 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；
> 
> **注：**前面逆向工程使用的mysql驱动依赖是用来生成pojo类、SqlMapper接口和里面的方法、SqlMapper.xml配置文件等的；和这里没有关系，这里还是要**重新引入mysql驱动依赖**！
> 
> 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：  
![7cb0811df3a144369ca284a8b877955a.png][]

（3）配置generatorConfig.xml（增强版）

![4511b89d7fc547d0bd56a58dfcd78e24.png][]

生成了两个pojo类，并且对于接口中的方法也变多了

![d04772251c9f4bc4b120475d3b35d7ea.png][]

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

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，创建CarExample对象，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：

![2e6a911fc8164d668ec5339564f789e7.png][]

[f55a2c81fb3149929759c34b9ecefe0d.png]: https://image.dandelioncloud.cn/pgy_files/images/2024/03/30/2d6123cda3914b42b90f4fbcd82e2a27.png
[8c30980efccb4733908483ea67a34027.png]: https://image.dandelioncloud.cn/pgy_files/images/2024/03/30/45f2cdbfe85c4edcb589e745eac02ae4.png
[7cb0811df3a144369ca284a8b877955a.png]: https://image.dandelioncloud.cn/pgy_files/images/2024/03/30/34a490ce99704d05b909e65face7e23a.png
[4511b89d7fc547d0bd56a58dfcd78e24.png]: https://image.dandelioncloud.cn/pgy_files/images/2024/03/30/72af2db486a6481ca3c6bd3fc0e9e7ca.png
[d04772251c9f4bc4b120475d3b35d7ea.png]: https://image.dandelioncloud.cn/pgy_files/images/2024/03/30/8cd872959047435f900a0e4f3bd97009.png
[2e6a911fc8164d668ec5339564f789e7.png]: https://image.dandelioncloud.cn/pgy_files/images/2024/03/30/0820a8ba8b7a44fe89f8a506f5d9817d.png