Mybatis核心配置mybatis-config解析以及sqlmapper文件的解析-----Mybatis框架
Mybatis核心配置mybatis-config解析以及sqlmapper文件的解析-----Mybatis框架
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mybatis小技巧 #{}和${}的区别 ${}的效果 org.apache.ibatis.exceptions.PersistenceException: ### Error querying database. Cause: java.sql.SQLSyntaxErrorException: Unknown column '新能源' in 'where clause' ### The error may exist in CarMapper.xml ### The error may involve defaultParameterMap ### The error occurred while setting parameters ### SQL: select id as id, car_num as carNum, brand as brand, guide_price as guidePrice, produce_time as produceTime, car_type as carType from t_car where car_type = 新能源 ### Cause: java.sql.SQLSyntaxErrorException: Unknown column '新能源' in 'where clause' 因为${}不会生成?然后直接以字段的形式填入了Sql语句 区别: #{}底层使用prepareStatement,先进行编译,然后用?传值 ${}底层使用statement,先进行拼接语句,再对语句进行编译(存在SQL注入风险) 可以扭曲原SQL语句的含义 如果向SQL中拼接表名,就需要使用${} 现实业务中,可能存在分表储存的情况,因为一张表存的话,数据量过大,查询效率比较低 可以将这些数据有规律的分表储存,这样在查询的时候效率比较高,因为扫描的数据量变少了 日志表,专门存储日志信息的,如果t_log,这个表中每天都会产生很多log,慢慢这个表内容会爆炸 可以每天生成一张表,每张表以当天日期作为名称 如果我们需要知道某天的日志信息怎么办 假设今天20230901,那么直接查询t_log_20230901即可 批量删除的写法,如何一次删除多条记录 第一种,delete from xxx where id = ? or id = ? or id = ? 第二种,delete from t_car where id in(1,2,3); //因为我们是通过拼接SQL的方式实现的,所以占位符会导致留下单引号 所以我们需要使用${}这个底层调用statement的方法的,因为它是先拼接后编译 #{}这个底层是preparedStatement,会先编译后拼接SQL语句 模糊查询like做法:需求根据汽车品牌进行查询 select * from t_car where brand like '%奔驰%'; select * from t_car where brand like '%比亚迪%'; 这个位置也不能用底层preparedStatement的#{}因为,会添加上''导致无法实现语义 第一种方案${} 第二种方案:使用concat函数,这个是mysql数据库专门用于字符串拼接的一个函数 concat('%',#{brand},'%') 第三种方案:concat('%','${brand}','%') 第四种方案:concat("%"#{brand}"%") nameSpace不能起别名,必须是全限定类名,带有包名在内的 <typeAliases> <!-- Type属性是指定哪个属性起别名,alias是指定别名--> <typeAlias type="com.powernode.mybatis.POJO.Car" alias="Car"></typeAlias> <typeAlias type="com.powernode.mybatis.POJO.Log" alias="Log"></typeAlias> </typeAliases> TypeAliases这个属性可以给我们的类起别名,起到简化的效果,必须在settings标签后配置 <TypeAliases>如果我们不指定别名,就自动以类名作为别名,在namespace下使用的时候,不区分大小写 Mapper标签可以用三个配置文件,resource和url和class,要求类的根路径必须有这个文件 resource是从根路径加载资源文件,url通过绝对路径找文件,这种方式移植性太差 class写的是全限定接口名,带有包名的,这个位置提供的是Mapper接口的全限定类名带包名的 如果写的是class,mybatis会自动去com.powernode.mybatis.Mapper下找这个XML文件 也就是说,这个Mapper接口必须是和xml在同一个文件夹下 建包只能在java包下实现,我们在Resource下只能建Directory而且他需要用/做层级切割mybatis小技巧 #{}和${}的区别 ${}的效果 org.apache.ibatis.exceptions.PersistenceException: ### Error querying database. Cause: java.sql.SQLSyntaxErrorException: Unknown column '新能源' in 'where clause' ### The error may exist in CarMapper.xml ### The error may involve defaultParameterMap ### The error occurred while setting parameters ### SQL: select id as id, car_num as carNum, brand as brand, guide_price as guidePrice, produce_time as produceTime, car_type as carType from t_car where car_type = 新能源 ### Cause: java.sql.SQLSyntaxErrorException: Unknown column '新能源' in 'where clause' 因为${}不会生成?然后直接以字段的形式填入了Sql语句 区别: #{}底层使用prepareStatement,先进行编译,然后用?传值 ${}底层使用statement,先进行拼接语句,再对语句进行编译(存在SQL注入风险) 可以扭曲原SQL语句的含义 如果向SQL中拼接表名,就需要使用${} 现实业务中,可能存在分表储存的情况,因为一张表存的话,数据量过大,查询效率比较低 可以将这些数据有规律的分表储存,这样在查询的时候效率比较高,因为扫描的数据量变少了 日志表,专门存储日志信息的,如果t_log,这个表中每天都会产生很多log,慢慢这个表内容会爆炸 可以每天生成一张表,每张表以当天日期作为名称 如果我们需要知道某天的日志信息怎么办 假设今天20230901,那么直接查询t_log_20230901即可 批量删除的写法,如何一次删除多条记录 第一种,delete from xxx where id = ? or id = ? or id = ? 第二种,delete from t_car where id in(1,2,3); //因为我们是通过拼接SQL的方式实现的,所以占位符会导致留下单引号 所以我们需要使用${}这个底层调用statement的方法的,因为它是先拼接后编译 #{}这个底层是preparedStatement,会先编译后拼接SQL语句 模糊查询like做法:需求根据汽车品牌进行查询 select * from t_car where brand like '%奔驰%'; select * from t_car where brand like '%比亚迪%'; 这个位置也不能用底层preparedStatement的#{}因为,会添加上''导致无法实现语义 第一种方案${} 第二种方案:使用concat函数,这个是mysql数据库专门用于字符串拼接的一个函数 concat('%',#{brand},'%') 第三种方案:concat('%','${brand}','%') 第四种方案:concat("%"#{brand}"%") nameSpace不能起别名,必须是全限定类名,带有包名在内的 <typeAliases> <!-- Type属性是指定哪个属性起别名,alias是指定别名--> <typeAlias type="com.powernode.mybatis.POJO.Car" alias="Car"></typeAlias> <typeAlias type="com.powernode.mybatis.POJO.Log" alias="Log"></typeAlias> </typeAliases> TypeAliases这个属性可以给我们的类起别名,起到简化的效果,必须在settings标签后配置 <TypeAliases>如果我们不指定别名,就自动以类名作为别名,在namespace下使用的时候,不区分大小写 Mapper标签可以用三个配置文件,resource和url和class,要求类的根路径必须有这个文件 resource是从根路径加载资源文件,url通过绝对路径找文件,这种方式移植性太差 class写的是全限定接口名,带有包名的,这个位置提供的是Mapper接口的全限定类名带包名的 如果写的是class,mybatis会自动去com.powernode.mybatis.Mapper下找这个XML文件 也就是说,这个Mapper接口必须是和xml在同一个文件夹下 建包只能在java包下实现,我们在Resource下只能建Directory而且他需要用/做层级切割
<?xml version="1.0" encoding="UTF-8" ?> <!DOCTYPE configuration PUBLIC "-//mybatis.org//DTD Config 3.0//EN" "http://mybatis.org/dtd/mybatis-3-config.dtd"> <configuration> <!-- 如果引入了三方可以不用写--> <properties resource="jdbc.properties"/> <settings> <setting name="logImpl" value="SLF4J"/> </settings> <typeAliases> <!-- Type属性是指定哪个属性起别名,alias是指定别名--> <!-- <typeAlias type="com.powernode.mybatis.POJO.Car" alias="Car"></typeAlias>--> <!-- <typeAlias type="com.powernode.mybatis.POJO.Log" alias="Log"></typeAlias>--> <!-- 写一个包名,将这些类自动指定别名,别名默认为类的名字--> <package name="com.powernode.mybatis.POJO"/> </typeAliases> <environments default="development"> <environment id="development"> <transactionManager type="JDBC" /> <dataSource type="POOLED"> <property name="driver" value="${jdbc.driver}" /> <property name="url" value="${jdbc.url}" /> <property name="username" value="${jdbc.username}" /> <property name="password" value="${jdbc.password}" /> </dataSource> </environment> </environments> <mappers> <!-- 指定xml文件的路径,自动从根路径下找资源--> <!-- <mapper class="com.powernode.mybatis.Mapper.CarMapper"></mapper>--> <!-- <mapper class="com.powernode.mybatis.Mapper.LogMapper"></mapper>--> <!-- url属性,是从绝对路径下加载资源的,语法格式是file:///加绝对路径--> <!-- <mapper resource="CarMapper.xml" url="file:///d:/CarMapper.xml"></mapper>--> <package name="com.powernode.mybatis.Mapper"/> </mappers> </configuration><?xml version="1.0" encoding="UTF-8" ?> <!DOCTYPE configuration PUBLIC "-//mybatis.org//DTD Config 3.0//EN" "http://mybatis.org/dtd/mybatis-3-config.dtd"> <configuration> <!-- 如果引入了三方可以不用写--> <properties resource="jdbc.properties"/> <settings> <setting name="logImpl" value="SLF4J"/> </settings> <typeAliases> <!-- Type属性是指定哪个属性起别名,alias是指定别名--> <!-- <typeAlias type="com.powernode.mybatis.POJO.Car" alias="Car"></typeAlias>--> <!-- <typeAlias type="com.powernode.mybatis.POJO.Log" alias="Log"></typeAlias>--> <!-- 写一个包名,将这些类自动指定别名,别名默认为类的名字--> <package name="com.powernode.mybatis.POJO"/> </typeAliases> <environments default="development"> <environment id="development"> <transactionManager type="JDBC" /> <dataSource type="POOLED"> <property name="driver" value="${jdbc.driver}" /> <property name="url" value="${jdbc.url}" /> <property name="username" value="${jdbc.username}" /> <property name="password" value="${jdbc.password}" /> </dataSource> </environment> </environments> <mappers> <!-- 指定xml文件的路径,自动从根路径下找资源--> <!-- <mapper class="com.powernode.mybatis.Mapper.CarMapper"></mapper>--> <!-- <mapper class="com.powernode.mybatis.Mapper.LogMapper"></mapper>--> <!-- url属性,是从绝对路径下加载资源的,语法格式是file:///加绝对路径--> <!-- <mapper resource="CarMapper.xml" url="file:///d:/CarMapper.xml"></mapper>--> <package name="com.powernode.mybatis.Mapper"/> </mappers> </configuration>
<?xml version="1.0" encoding="UTF-8" ?> <configuration debug="false"> <appender name="STDOUT" class="ch.qos.logback.core.ConsoleAppender"> <encoder class="ch.qos.logback.classic.encoder.PatternLayoutEncoder"> <pattern>%d{yyyy-MM-dd HH:mm:ss.SSS} [%thread] %-5level %logger{50} - %msg%n</pattern> </encoder> </appender> <logger name="org.apache.ibatis" level="TRACE"> </logger> <logger name="java.sql.Connection" level="DEBUG"> </logger> <logger name="java.sql.Statement" level="DEBUG"> </logger> <logger name="java.sql.PreparedStatement" level="DEBUG"> </logger> <!--日志级别,由低到高--> <!--ALL < TRACE < DEBUG < INFO < WARN < ERROR < FATAL < OFF--> <root level="DEBUG"> <appender-ref ref="STDOUT"> </appender-ref> <appender-ref ref="FILE"> </appender-ref> </root> </configuration><?xml version="1.0" encoding="UTF-8" ?> <configuration debug="false"> <appender name="STDOUT" class="ch.qos.logback.core.ConsoleAppender"> <encoder class="ch.qos.logback.classic.encoder.PatternLayoutEncoder"> <pattern>%d{yyyy-MM-dd HH:mm:ss.SSS} [%thread] %-5level %logger{50} - %msg%n</pattern> </encoder> </appender> <logger name="org.apache.ibatis" level="TRACE"> </logger> <logger name="java.sql.Connection" level="DEBUG"> </logger> <logger name="java.sql.Statement" level="DEBUG"> </logger> <logger name="java.sql.PreparedStatement" level="DEBUG"> </logger> <!--日志级别,由低到高--> <!--ALL < TRACE < DEBUG < INFO < WARN < ERROR < FATAL < OFF--> <root level="DEBUG"> <appender-ref ref="STDOUT"> </appender-ref> <appender-ref ref="FILE"> </appender-ref> </root> </configuration>
jdbc.driver=com.mysql.cj.jdbc.Driver jdbc.url=jdbc:mysql://localhost:13306/powernode jdbc.username=root jdbc.password=abc123jdbc.driver=com.mysql.cj.jdbc.Driver jdbc.url=jdbc:mysql://localhost:13306/powernode jdbc.username=root jdbc.password=abc123
<?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.powernode.mybatis.Mapper.CarMapper"> <delete id="deleteBatch"> delete from t_car where car_num in (${carNums}); </delete> <select id="selectByBrand" resultType="Car"> select id as id, car_num as carNum, brand as brand, guide_price as guidePrice, produce_time as produceTime, car_type as carType from t_car where -- brand like '%${brand}%' -- brand like concat('%',#{brand},'%') brand like concat('%','${brand}','%') brand like concat("%"#{brand}"%") </select> <select id="selectByCarType" resultType="Car"> select id as id, car_num as carNum, brand as brand, guide_price as guidePrice, produce_time as produceTime, car_type as carType from t_car where car_type = #{carType} </select> <select id="selectAllByAscOrDesc" resultType="Car"> select id as id, car_num as carNum, brand as brand, guide_price as guidePrice, produce_time as produceTime, car_type as carType from t_car order by guide_price ${DescOrAsc}; </select> </mapper><?xml version="1.0" encoding="UTF-8"?> <!DOCTYPE mapper PUBLIC "-//mybatis.org//DTD Mapper 3.0//EN" "http://mybatis.org/dtd/mybatis-3-mapper.dtd"> <mapper namespace="com.powernode.mybatis.Mapper.CarMapper"> <delete id="deleteBatch"> delete from t_car where car_num in (${carNums}); </delete> <select id="selectByBrand" resultType="Car"> select id as id, car_num as carNum, brand as brand, guide_price as guidePrice, produce_time as produceTime, car_type as carType from t_car where -- brand like '%${brand}%' -- brand like concat('%',#{brand},'%') brand like concat('%','${brand}','%') brand like concat("%"#{brand}"%") </select> <select id="selectByCarType" resultType="Car"> select id as id, car_num as carNum, brand as brand, guide_price as guidePrice, produce_time as produceTime, car_type as carType from t_car where car_type = #{carType} </select> <select id="selectAllByAscOrDesc" resultType="Car"> select id as id, car_num as carNum, brand as brand, guide_price as guidePrice, produce_time as produceTime, car_type as carType from t_car order by guide_price ${DescOrAsc}; </select> </mapper>
<?xml version="1.0" encoding="UTF-8"?> <!DOCTYPE mapper PUBLIC "-//mybatis.org//DTD Mapper 3.0//EN" "http://mybatis.org/dtd/mybatis-3-mapper.dtd"> <mapper namespace="com.powernode.mybatis.Mapper.LogMapper"> <select id="selectAllByTable" resultType="Log"> select * from t_log_${date}; </select> </mapper><?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.powernode.mybatis.Mapper.LogMapper"> <select id="selectAllByTable" resultType="Log"> select * from t_log_${date}; </select> </mapper>
package com.powernode.mybatis.Mapper; import com.powernode.mybatis.POJO.Car; import java.util.List; public interface CarMapper { //根据汽车类型,获取汽车信息 List<Car> selectByCarType(String carType); //查询所有的汽车信息,通过DESC或者ASC升降序 List<Car> selectAllByAscOrDesc(String AscOrDesc); //根据ID进行批量删除 int deleteBatch(String carNums); List<Car> selectByBrand(String brand); }package com.powernode.mybatis.Mapper; import com.powernode.mybatis.POJO.Car; import java.util.List; public interface CarMapper { //根据汽车类型,获取汽车信息 List<Car> selectByCarType(String carType); //查询所有的汽车信息,通过DESC或者ASC升降序 List<Car> selectAllByAscOrDesc(String AscOrDesc); //根据ID进行批量删除 int deleteBatch(String carNums); List<Car> selectByBrand(String brand); }
package com.powernode.mybatis.Mapper; import com.powernode.mybatis.POJO.Log; import java.util.List; public interface LogMapper { //根据日期查询不同的表,获取表中所有的日志 List<Log> selectAllByTable(String time); }package com.powernode.mybatis.Mapper; import com.powernode.mybatis.POJO.Log; import java.util.List; public interface LogMapper { //根据日期查询不同的表,获取表中所有的日志 List<Log> selectAllByTable(String time); }
package com.powernode.mybatis.POJO; public class Car { //这是一个封装汽车相关信息的普通的java类,数据库表中的字段应该和属性一一对应 //为什么使用包装类,因为当我们查值的时候,返回值有可能是null //避免数据不兼容 private Long id; private String carNum; private String brand; private Double guidePrice; private String produceTime; private String carType; public Car(){}; public Car(Long id, String carNum, String brand, Double guidePrice, String produceTime, String carType) { this.id = id; this.carNum = carNum; this.brand = brand; this.guidePrice = guidePrice; this.produceTime = produceTime; this.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; } public String getBrand() { return brand; } public void setBrand(String brand) { this.brand = brand; } public Double getGuidePrice() { return guidePrice; } public void setGuidePrice(Double guidePrice) { this.guidePrice = guidePrice; } public String getProduceTime() { return produceTime; } public void setProduceTime(String produceTime) { this.produceTime = produceTime; } public String getCarType() { return carType; } public void setCarType(String carType) { this.carType = carType; } @Override public String toString() { return "Car{" + "id=" + id + ", carNum='" + carNum + '\'' + ", brand='" + brand + '\'' + ", guidePrice=" + guidePrice + ", produceTime='" + produceTime + '\'' + ", carType='" + carType + '\'' + '}'; } }package com.powernode.mybatis.POJO; public class Car { //这是一个封装汽车相关信息的普通的java类,数据库表中的字段应该和属性一一对应 //为什么使用包装类,因为当我们查值的时候,返回值有可能是null //避免数据不兼容 private Long id; private String carNum; private String brand; private Double guidePrice; private String produceTime; private String carType; public Car(){}; public Car(Long id, String carNum, String brand, Double guidePrice, String produceTime, String carType) { this.id = id; this.carNum = carNum; this.brand = brand; this.guidePrice = guidePrice; this.produceTime = produceTime; this.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; } public String getBrand() { return brand; } public void setBrand(String brand) { this.brand = brand; } public Double getGuidePrice() { return guidePrice; } public void setGuidePrice(Double guidePrice) { this.guidePrice = guidePrice; } public String getProduceTime() { return produceTime; } public void setProduceTime(String produceTime) { this.produceTime = produceTime; } public String getCarType() { return carType; } public void setCarType(String carType) { this.carType = carType; } @Override public String toString() { return "Car{" + "id=" + id + ", carNum='" + carNum + '\'' + ", brand='" + brand + '\'' + ", guidePrice=" + guidePrice + ", produceTime='" + produceTime + '\'' + ", carType='" + carType + '\'' + '}'; } }
package com.powernode.mybatis.POJO; public class Log { private Long id; private String log; private String time; @Override public String toString() { return "Log{" + "id=" + id + ", log='" + log + '\'' + ", time='" + time + '\'' + '}'; } public Long getId() { return id; } public void setId(Long id) { this.id = id; } public String getLog() { return log; } public void setLog(String log) { this.log = log; } public String getTime() { return time; } public void setTime(String time) { this.time = time; } public Log(Long id, String log, String time) { this.id = id; this.log = log; this.time = time; } public Log() { } }package com.powernode.mybatis.POJO; public class Log { private Long id; private String log; private String time; @Override public String toString() { return "Log{" + "id=" + id + ", log='" + log + '\'' + ", time='" + time + '\'' + '}'; } public Long getId() { return id; } public void setId(Long id) { this.id = id; } public String getLog() { return log; } public void setLog(String log) { this.log = log; } public String getTime() { return time; } public void setTime(String time) { this.time = time; } public Log(Long id, String log, String time) { this.id = id; this.log = log; this.time = time; } public Log() { } }
package com.powernode.mybatis.utils; 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 java.io.IOException; public class SqlSessionUtils { private SqlSessionUtils(){} private static SqlSessionFactory sqlSessionFactory; private static ThreadLocal<SqlSession> local = new ThreadLocal<>(); static { try { sqlSessionFactory = new SqlSessionFactoryBuilder().build(Resources.getResourceAsStream("mybatis-config.xml")); } catch (IOException e) { throw new RuntimeException(e); } } public static SqlSession openSession() { SqlSession sqlSession = local.get(); if (sqlSession == null) { sqlSession = sqlSessionFactory.openSession(); local.set(sqlSession); } return sqlSession; } public static void close(SqlSession sqlSession) { if(sqlSession != null) { sqlSession.close(); local.remove(); } } }package com.powernode.mybatis.utils; 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 java.io.IOException; public class SqlSessionUtils { private SqlSessionUtils(){} private static SqlSessionFactory sqlSessionFactory; private static ThreadLocal<SqlSession> local = new ThreadLocal<>(); static { try { sqlSessionFactory = new SqlSessionFactoryBuilder().build(Resources.getResourceAsStream("mybatis-config.xml")); } catch (IOException e) { throw new RuntimeException(e); } } public static SqlSession openSession() { SqlSession sqlSession = local.get(); if (sqlSession == null) { sqlSession = sqlSessionFactory.openSession(); local.set(sqlSession); } return sqlSession; } public static void close(SqlSession sqlSession) { if(sqlSession != null) { sqlSession.close(); local.remove(); } } }
package com.powernode.mybatis.Test;
import com.powernode.mybatis.Mapper.CarMapper;
import com.powernode.mybatis.Mapper.LogMapper;
import com.powernode.mybatis.POJO.Car;
import com.powernode.mybatis.POJO.Log;
import com.powernode.mybatis.utils.SqlSessionUtils;
import org.apache.ibatis.session.SqlSession;
import org.junit.Test;
import java.util.Iterator;
import java.util.List;
public class CarMapperTest
{
@Test
public void TestMapper()
{
SqlSession sqlSession = SqlSessionUtils.openSession();
CarMapper mapper = sqlSession.getMapper(CarMapper.class);
List<Car> carList = mapper.selectByCarType("新能源");
carList.forEach(car ->
{
System.out.println(car);
});
SqlSessionUtils.close(sqlSession);
}
@Test
public void TestDescOrAsc()
{
SqlSession sqlSession = SqlSessionUtils.openSession();
CarMapper mapper = sqlSession.getMapper(CarMapper.class);
List<Car> carList = mapper.selectAllByAscOrDesc("DESC");
carList.forEach(car -> {
System.out.println(car);
});
SqlSessionUtils.close(sqlSession);
}
@Test
public void TestLog()
{
SqlSession sqlSession = SqlSessionUtils.openSession();
LogMapper mapper = sqlSession.getMapper(LogMapper.class);
List<Log> logs = mapper.selectAllByTable("20230902");
Iterator<Log> iterator = logs.iterator();
while(iterator.hasNext())
{
System.out.println((Log)iterator.next());
}
}
@Test
public void TestDelete()
{
SqlSession sqlSession = SqlSessionUtils.openSession();
CarMapper mapper = sqlSession.getMapper(CarMapper.class);
int count = mapper.deleteBatch("1003,1111");
System.out.println(count);
sqlSession.commit();
SqlSessionUtils.close(sqlSession);
}
@Test
public void SelectByBrandLike()
{
SqlSession sqlSession = SqlSessionUtils.openSession();
CarMapper mapper = sqlSession.getMapper(CarMapper.class);
List<Car> carList = mapper.selectByBrand("比亚迪");
carList.forEach(car -> {
System.out.println(car);
});
}
}
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