2022.1.17-18 Javaweb Mybatis快速入门完成增删改查

2023-11-06 16:20
文章标签 java 入门 快速 web 完成 18 17 mybatis 改查 增删 2022.1

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Mybatis
Mybatis是持久层框架，简化JDBC开发。
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create database mybatis;
use mybatis;drop table if exists tb_user;create table tb_user(id int primary key auto_increment,username varchar(20),password varchar(20),gender char(1),addr varchar(30)
);INSERT INTO tb_user VALUES (1, 'zhangsan', '123', '男', '北京');
INSERT INTO tb_user VALUES (2, '李四', '234', '女', '天津');
INSERT INTO tb_user VALUES (3, '王五', '11', '男', '西安');

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pom.xml

<?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>org.example</groupId><artifactId>mybatis-demo</artifactId><version>1.0-SNAPSHOT</version><dependencies><dependency><groupId>org.mybatis</groupId><artifactId>mybatis</artifactId><version>3.5.5</version></dependency><dependency><groupId>mysql</groupId><artifactId>mysql-connector-java</artifactId><version>5.1.46</version></dependency><dependency><groupId>junit</groupId><artifactId>junit</artifactId><version>4.13</version><scope>test</scope></dependency><!-- 添加slf4j日志api --><dependency><groupId>org.slf4j</groupId><artifactId>slf4j-api</artifactId><version>1.7.20</version></dependency><!-- 添加logback-classic依赖 --><dependency><groupId>ch.qos.logback</groupId><artifactId>logback-classic</artifactId><version>1.2.3</version></dependency><!-- 添加logback-core依赖 --><dependency><groupId>ch.qos.logback</groupId><artifactId>logback-core</artifactId><version>1.2.3</version></dependency></dependencies>
</project>

mybatis-config.xml

<?xml version="1.0" encoding="UTF-8" ?>
<!DOCTYPE configurationPUBLIC "-//mybatis.org//DTD Config 3.0//EN""http://mybatis.org/dtd/mybatis-3-config.dtd">
<configuration><environments default="development"><environment id="development"><transactionManager type="JDBC"/><dataSource type="POOLED"><property name="driver" value="com.mysql.jdbc.Driver"/><property name="url" value="jdbc:mysql://localhost:3306/mybatis?allowPublicKeyRetrieval=true&amp;useSSL=false"/><property name="username" value="root"/><property name="password" value="root"/></dataSource></environment></environments><mappers><!--加载sql映射文件--><mapper resource="UserMapper.xml"/></mappers>
</configuration>

UserMapper.xml

<?xml version="1.0" encoding="UTF-8" ?>
<!DOCTYPE mapperPUBLIC "-//mybatis.org//DTD Mapper 3.0//EN""http://mybatis.org/dtd/mybatis-3-mapper.dtd"><mapper namespace="test"><select id="selectAll" resultType="com.itest.pojo.User">select * from tb_user;</select>
</mapper>

User.java

package com.itest.pojo;/*** @Description: TODO* @author: scott* @date: 2022年01月17日 9:17*/
public class User {private Integer id;private String username;private String password;private String gender;private String addr;public Integer getId() {return id;}public void setId(Integer id) {this.id = id;}public String getUsername() {return username;}public void setUsername(String username) {this.username = username;}public String getPassword() {return password;}public void setPassword(String password) {this.password = password;}public String getGender() {return gender;}public void setGender(String gender) {this.gender = gender;}public String getAddr() {return addr;}public void setAddr(String addr) {this.addr = addr;}@Overridepublic String toString() {return "User{" +"id=" + id +", username='" + username + '\'' +", password='" + password + '\'' +", gender='" + gender + '\'' +", addr='" + addr + '\'' +'}';}
}

MyBatisDemo.java

package com.itest.pojo;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;
import java.io.InputStream;
import java.util.List;/*** @Description: TODO* @author: scott* @date: 2022年01月17日 9:26*/
public class MyBatisDemo {public static void main(String[] args) throws IOException {//加载核心配置文件，获取sqlsessionFactoryString resource = "mybatis-config.xml";InputStream inputStream = Resources.getResourceAsStream(resource);SqlSessionFactory sqlSessionFactory = new SqlSessionFactoryBuilder().build(inputStream);//获取sqlsession对象，用它来执行sqlSqlSession sqlSession = sqlSessionFactory.openSession();//执行sqlList<User> users = sqlSession.selectList("test.selectAll");System.out.println(users);//释放资源sqlSession.close();}
}

Mapper代理开发

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即可用 <package name="com.itest.mapper"/> 简化。

Mybatis核心文件配置
enviroment :配置数据库连接环境信息，可以配置多个environment，通过default属性切换不同的environment。
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配置各个标签时，需要遵守前后顺序。

配置文件完成增删改查
sql语句

-- 删除tb_brand表
drop table if exists tb_brand;
-- 创建tb_brand表
create table tb_brand
(-- id 主键id           int primary key auto_increment,-- 品牌名称brand_name   varchar(20),-- 企业名称company_name varchar(20),-- 排序字段ordered      int,-- 描述信息description  varchar(100),-- 状态：0：禁用  1：启用status       int
);
-- 添加数据
insert into tb_brand (brand_name, company_name, ordered, description, status)
values ('三只松鼠', '三只松鼠股份有限公司', 5, '好吃不上火', 0),('华为', '华为技术有限公司', 100, '华为致力于把数字世界带入每个人、每个家庭、每个组织，构建万物互联的智能世界', 1),('小米', '小米科技有限公司', 50, 'are you ok', 1);SELECT * FROM tb_brand;

Brand类

package com.itest.pojo;/*** 品牌** alt + 鼠标左键：整列编辑** 在实体类中，基本数据类型建议使用其对应的包装类型*/public class Brand {// id 主键private Integer id;// 品牌名称private String brandName;// 企业名称private String companyName;// 排序字段private Integer ordered;// 描述信息private String description;// 状态：0：禁用  1：启用private Integer status;public Integer getId() {return id;}public void setId(Integer id) {this.id = id;}public String getBrandName() {return brandName;}public void setBrandName(String brandName) {this.brandName = brandName;}public String getCompanyName() {return companyName;}public void setCompanyName(String companyName) {this.companyName = companyName;}public Integer getOrdered() {return ordered;}public void setOrdered(Integer ordered) {this.ordered = ordered;}public String getDescription() {return description;}public void setDescription(String description) {this.description = description;}public Integer getStatus() {return status;}public void setStatus(Integer status) {this.status = status;}@Overridepublic String toString() {return "Brand{" +"id=" + id +", brandName='" + brandName + '\'' +", companyName='" + companyName + '\'' +", ordered=" + ordered +", description='" + description + '\'' +", status=" + status +'}';}
}

查询所有数据
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定义实体类Brand.java

package com.itest.pojo;/*** 品牌** alt + 鼠标左键：整列编辑** 在实体类中，基本数据类型建议使用其对应的包装类型*/public class Brand {// id 主键private Integer id;// 品牌名称private String brandName;// 企业名称private String companyName;// 排序字段private Integer ordered;// 描述信息private String description;// 状态：0：禁用  1：启用private Integer status;public Integer getId() {return id;}public void setId(Integer id) {this.id = id;}public String getBrandName() {return brandName;}public void setBrandName(String brandName) {this.brandName = brandName;}public String getCompanyName() {return companyName;}public void setCompanyName(String companyName) {this.companyName = companyName;}public Integer getOrdered() {return ordered;}public void setOrdered(Integer ordered) {this.ordered = ordered;}public String getDescription() {return description;}public void setDescription(String description) {this.description = description;}public Integer getStatus() {return status;}public void setStatus(Integer status) {this.status = status;}@Overridepublic String toString() {return "Brand{" +"id=" + id +", brandName='" + brandName + '\'' +", companyName='" + companyName + '\'' +", ordered=" + ordered +", description='" + description + '\'' +", status=" + status +'}';}
}

在Mapper中定义BrandMapper.java

package com.itest.mapper;import com.itest.pojo.Brand;
import java.util.List;public interface BrandMapper {public List<Brand> selectAll();}

在resources里创建BrandMapper.xml

<?xml version="1.0" encoding="UTF-8" ?>
<!DOCTYPE mapperPUBLIC "-//mybatis.org//DTD Mapper 3.0//EN""http://mybatis.org/dtd/mybatis-3-mapper.dtd"><mapper namespace="com.itest.mapper.BrandMapper"><select id="selectAll" resultType="com.itest.pojo.Brand">select * from tb_brand;</select>
</mapper>

最后在test中新建MyBatisTest.java

package com.itest.pojo;import com.itest.mapper.BrandMapper;
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;
import java.io.InputStream;
import java.util.List;/*** @Description: TODO* @author: scott* @date: 2022年01月17日 9:26*/
public class MyBatisDemo {public static void main(String[] args) throws IOException {//加载核心配置文件，获取sqlsessionFactoryString resource = "mybatis-config.xml";InputStream inputStream = Resources.getResourceAsStream(resource);SqlSessionFactory sqlSessionFactory = new SqlSessionFactoryBuilder().build(inputStream);//获取sqlsession对象，用它来执行sqlSqlSession sqlSession = sqlSessionFactory.openSession();//获取Mapper接口的代理对象BrandMapper brandMapper = sqlSession.getMapper(BrandMapper.class);//执行方法List<Brand> brands = brandMapper.selectAll();System.out.println(brands);//释放资源sqlSession.close();}
}

结果显示如下：
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有字段显示为null。因为Java中驼峰命名与数据库名称不一致。
解决方案有以下两种：

1.对不一样的列名起别名，让别名和实体类的属性一样。

    <select id="selectAll" resultType="com.itest.pojo.Brand">select id,brand_name as brandName,company_name as companyName,ordered,description,statusfrom tb_brand;</select>

结果：
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如果觉得每次写很多列名很麻烦 ，可以用sql片段方式来引用。代码如下：

    <sql id="brand_column">id,brand_name as brandName,company_name as companyName,ordered,description,status</sql><select id="selectAll" resultType="com.itest.pojo.Brand">select<include refid="brand_column"> </include>from tb_brand;</select>

2.用resultmap来解决

    <resultMap id="resultBrand" type="com.itest.pojo.Brand"><result column="brand_name" property="brandName"/><result column="company_name" property="companyName"/></resultMap><select id="selectAll" resultMap="resultBrand">select *from tb_brand;</select>

主键用<id>,其他用<result>

查询-查看详情
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BrandMapper.java中定义方法

package com.itest.mapper;
import com.itest.pojo.Brand;
import java.util.List;
public interface BrandMapper {public Brand selectById(int id);
}

BrandMapper.xml中写SQL语句

<?xml version="1.0" encoding="UTF-8" ?>
<!DOCTYPE mapperPUBLIC "-//mybatis.org//DTD Mapper 3.0//EN""http://mybatis.org/dtd/mybatis-3-mapper.dtd"><mapper namespace="com.itest.mapper.BrandMapper"><resultMap id="resultBrand" type="com.itest.pojo.Brand"><result column="brand_name" property="brandName"/><result column="company_name" property="brandName"/></resultMap><select id="selectAll" resultMap="resultBrand">select *from tb_brand;</select><select id="selectById" resultMap="resultBrand">select * from tb_brand where id = #{id};</select>
</mapper>

在MyBatisTest.java中测试

package com.itest.test;import com.itest.mapper.BrandMapper;
import com.itest.mapper.UserMapper;
import com.itest.pojo.Brand;
import com.itest.pojo.User;
import org.apache.ibatis.io.Resources;
import org.apache.ibatis.session.SqlSession;
import org.apache.ibatis.session.SqlSessionFactory;
import org.apache.ibatis.session.SqlSessionFactoryBuilder;
import org.junit.Test;import java.io.IOException;
import java.io.InputStream;
import java.util.List;/*** @Description: TODO* @author: scott* @date: 2022年01月17日 15:08*/
public class MyBatisTest {@Testpublic void selectById() throws IOException {//模拟接收参数int id =1;//获取SqlsessionFactoryString resource = "mybatis-config.xml";InputStream inputStream = Resources.getResourceAsStream(resource);SqlSessionFactory sqlSessionFactory = new SqlSessionFactoryBuilder().build(inputStream);//获取Sqlsession对象SqlSession sqlSession = sqlSessionFactory.openSession();BrandMapper brandMapper = sqlSession.getMapper(BrandMapper.class);Brand brand = brandMapper.selectById(id);System.out.println(brand);//释放资源sqlSession.close();}
}

得到结果：
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·注意：参数占位符：
1.#{ } :会将其替换为？，为了防止SQL注入
2.${ } :会存在SQL注入问题
使用参数传递的时候统一使用#{ }

参数类型可以省略，不省略如下：

<select id="selectById"  parameterType="int"  resultMap="resultBrand">select * from tb_brand where id = #{id};
</select>

XML中<会报错，解决方法有两种
1.转义字符  如<的转义字符为&lt;     
2.CDATA区  如小于号如下：<![CDATA[<]]>

条件查询-多条件查询
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1.散装参数格式：注意@Param（" xxx"）中xxx需要对应占位符名称 status = #{ status }
2.如果都来自同一对象，则 List<Brand>selectByCondition(Brand brand); 这样 status = #{ status } 就会到对象brand中去匹配属性。
3.封装成map，map键的名称与占位符保持一致，List<Brand>selectByCondition(Map map);

代码实现:
1.
BrandMapper.xml代码

    <select id = "selectByCondition"   resultMap="resultBrand">select * from tb_brandwhere status = #{status}and brand_name like #{brandName}and company_name like #{companyName}</select>

BrandMapper.java代码

public interface BrandMapper {List <Brand> selectByCondition(@Param("status") int status, @Param("companyName") String companyName,@Param("brandName") String brandName);
}

MyBatisTest.java测试核心代码

		//模拟接收参数int status =1;String brandName = "华为";String companyName = "华为";//处理参数brandName ="%"+brandName+"%";companyName = "%"+companyName+"%";···List<Brand> brands =  brandMapper.selectByCondition(status,companyName,brandName);System.out.println(brands);

运行结果
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2.
BrandMapper.xml代码不需要修改

    <select id = "selectByCondition"   resultMap="resultBrand">select * from tb_brandwhere status = #{status}and brand_name like #{brandName}and company_name like #{companyName}</select>

BrandMapper.java

public interface BrandMapper {List<Brand> selectByCondition(Brand brand);}

MyBatisTest.java

 //模拟接收参数int status =1;String brandName = "华为";String companyName = "华为";//处理参数brandName ="%"+brandName+"%";companyName = "%"+companyName+"%";//封装对象Brand brand = new Brand();brand.setStatus(status);brand.setBrandName(companyName);brand.setCompanyName(brandName);···List<Brand> brands =  brandMapper.selectByCondition(brand);System.out.println(brands);

结果
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3.
BrandMapper.xml中不需要修改

    <select id = "selectByCondition"   resultMap="resultBrand">select * from tb_brandwhere status = #{status}and brand_name like #{brandName}and company_name like #{companyName}</select>

BrandMapper.java

public interface BrandMapper {List<Brand> selectByCondition(Map map);}

MyBatisTest.java核心代码

		//模拟接收参数int status =1;String brandName = "华为";String companyName = "华为";//处理参数brandName ="%"+brandName+"%";companyName = "%"+companyName+"%";//map 封装对象Map map = new HashMap();map.put("status",status);map.put("brandName",brandName);map.put("companyName",companyName);···List<Brand> brands =  brandMapper.selectByCondition(map);System.out.println(brands);

运行结果
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总结多条件查询
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动态SQL
针对上面多条件查询，无法满足仅填一个条件时完成正确查询结果。对此，mybatis提供强大的动态sql支撑。
·if
·choose(when,otherwise)
·trim(where,set)
·foreach

通过<if>标签来改造sql，代码如下

    <select id = "selectByCondition"   resultMap="resultBrand">select * from tb_brandwhere<if test="status != null">status = #{status}</if><if test="brandName !=null and brandName!='' ">and brand_name like #{brandName}</if><if test="companyName !=null and companyName!='' ">and company_name like #{companyName}</if></select>

其中Sting类型 判断条件是：不等于空，也不等于空字符串

新问题：如果status为空 则 后面语句格式不对 报错

org.apache.ibatis.exceptions.PersistenceException: ### Error
querying database. Cause:
com.mysql.jdbc.exceptions.jdbc4.MySQLSyntaxErrorException: You have an
error in your SQL syntax

改进方法1：恒等式  统一加and

    <select id = "selectByCondition"   resultMap="resultBrand">select * from tb_brandwhere  1=1<if test="status != null">and status = #{status}</if><if test="brandName !=null and brandName!='' ">and brand_name like #{brandName}</if><if test="companyName !=null and companyName!='' ">and company_name like #{companyName}</if></select>

改进方法二：mybatis<where>标签替换where关键字

    <select id = "selectByCondition"   resultMap="resultBrand">select * from tb_brand<where><if test="status != null">and status = #{status}</if><if test="brandName !=null and brandName!='' ">and brand_name like #{brandName}</if><if test="companyName !=null and companyName!='' ">and company_name like #{companyName}</if></where></select>

单条件-动态条件查询
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public interface BrandMapper {List<Brand> selectSingleCondition(Brand brand);}

BrandMapper.xml

    <select id = "selectSingleCondition"   resultMap="resultBrand">select * from tb_brand<where><choose><when test="status!=null">status=#{status}</when><when test="brandName!=null  and brandName!=''  ">brand_name  like  #{brandName}</when><when test="companyName!=null and companyName!='' ">company_name  like #{companyName}</when></choose></where></select>

MyBatisTest.java

 //模拟接收参数int status =1;String brandName = "华为";String companyName = "华为";//处理参数brandName ="%"+brandName+"%";companyName = "%"+companyName+"%";//封装对象Brand brand = new Brand();// brand.setStatus(status);brand.setBrandName(companyName);//brand.setCompanyName(brandName);···List<Brand> brands1 = brandMapper.selectSingleCondition(brand);System.out.println(brands1);

添加（增、删、改都需要提交事务 ，不然无法修改数据库信息）
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BrandMapper.java

public interface BrandMapper {void add(Brand brand);}

BrandMapper.xml

    <insert id="add" >insert into tb_brand (brand_name,company_name,ordered,description,status)values (#{brandName},#{companyName},#{ordered},#{description},#{status});</insert>

MyBatisTest.java

    @Testpublic void add() throws IOException {//模拟接收参数String brandName = "小米手机";String companyName = "小米";int ordered =100;String description ="为发烧而生";int status =1;//封装参数Brand brand = new Brand();brand.setBrandName(brandName);brand.setCompanyName(companyName);brand.setOrdered(ordered);brand.setDescription(description);brand.setStatus(status);//获取SqlsessionFactoryString resource = "mybatis-config.xml";InputStream inputStream = Resources.getResourceAsStream(resource);SqlSessionFactory sqlSessionFactory = new SqlSessionFactoryBuilder().build(inputStream);//获取Sqlsession对象SqlSession sqlSession = sqlSessionFactory.openSession();BrandMapper brandMapper = sqlSession.getMapper(BrandMapper.class);//执行方法brandMapper.add(brand);//提交事务sqlSession.commit();//释放资源sqlSession.close();}

添加-主键返回
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若要在新增完成后获取主键id ，在insert标签中定义两个量:
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修改全部字段
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BrandMapper.java

public interface BrandMapper {int update(Brand brand);
}

BrandMapper.xml

    <update id="update">update tb_brandsetbrand_name = #{brandName},company_name = #{companyName},ordered = #{ordered},description = #{description},status = #{status}where id = #{id};</update>

MyBatisTest.java

 @Testpublic void update() throws IOException {//模拟接收参数String brandName = "ooo";String companyName = "oo";int ordered =100;String description ="1111111";int status =1;int id =5;//封装参数Brand brand = new Brand();brand.setBrandName(brandName);brand.setCompanyName(companyName);brand.setOrdered(ordered);brand.setDescription(description);brand.setStatus(status);brand.setId(id);//获取SqlsessionFactoryString resource = "mybatis-config.xml";InputStream inputStream = Resources.getResourceAsStream(resource);SqlSessionFactory sqlSessionFactory = new SqlSessionFactoryBuilder().build(inputStream);//获取Sqlsession对象SqlSession sqlSession = sqlSessionFactory.openSession();BrandMapper brandMapper = sqlSession.getMapper(BrandMapper.class);//执行方法int count = brandMapper.update(brand);System.out.println(count);//提交事务sqlSession.commit();//释放资源sqlSession.close();}

修改动态字段
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利用<set>标签可以避免出错；
即在BrandMapper.xml中修改为：

    <update id="update">update tb_brand<set><if test="brandName!=null  and brandName!=''">brand_name = #{brandName},</if><if test="companyName!=null  and companyName!=''">company_name = #{companyName},</if><if test="ordered!=null ">ordered = #{ordered},</if><if test="description!=null  and description!=''">description = #{description},</if><if test="status!=null">status = #{status}</if></set>where id = #{id};</update>

删除
BrandMapper.java

public interface BrandMapper {void deleteById(int id);
}

BrandMapper.xml

    <delete id="deleteById">delete from tb_brand where id =#{id};</delete>

MyBatisTest.java

@Testpublic void deleteById() throws IOException {//模拟接收参数int id =5;//获取SqlsessionFactoryString resource = "mybatis-config.xml";InputStream inputStream = Resources.getResourceAsStream(resource);SqlSessionFactory sqlSessionFactory = new SqlSessionFactoryBuilder().build(inputStream);//获取Sqlsession对象SqlSession sqlSession = sqlSessionFactory.openSession();BrandMapper brandMapper = sqlSession.getMapper(BrandMapper.class);//执行方法brandMapper.deleteById(id);//提交事务sqlSession.commit();//释放资源sqlSession.close();}
}

批量删除
会把选中的ID封装成一个数组，在根据数组的值把对应id全部删除。
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<foreach collection=“ids” item =“id” >
利用foreach来遍历集合，其中collection表明指定便利的数组，item指定便利的元素

mybatis中会将数组参数，封装为一个Map集合。
*默认：array = 数组 *在.java中使用@Param注解来改变map集合的默认key的名称
如void deleteByIds（@Param("ids")"ids"）int [] ids);
则.xml中可以使用：<foreach collection = "ids"></foreach>

代码如下：
BrandMapper.java

public interface BrandMapper {void deleteByIds(@Param("ids") int[] ids);
}

BrandMapper.xml

    <delete id="deleteByIds">delete from tb_brandwhere id in<foreach collection="ids" item="id" separator="," open="(" close=")">#{id}</foreach></delete>

MyBatisTest.java

    @Testpublic void deleteByIds() throws IOException {//模拟接收参数int[] ids = {6,7};//获取SqlsessionFactoryString resource = "mybatis-config.xml";InputStream inputStream = Resources.getResourceAsStream(resource);SqlSessionFactory sqlSessionFactory = new SqlSessionFactoryBuilder().build(inputStream);//获取Sqlsession对象SqlSession sqlSession = sqlSessionFactory.openSession();BrandMapper brandMapper = sqlSession.getMapper(BrandMapper.class);//执行方法brandMapper.deleteByIds(ids);//提交事务sqlSession.commit();//释放资源sqlSession.close();}

MyBatis参数传递
在这里插入图片描述
在这里插入图片描述
注解开发
在这里插入图片描述
代码如下：
BrandMapper.java

@Select("select * from tb_brand where id = #{id}")
Brand selectById(int id);

MyBatisTest.java

    @Testpublic void selecttest() throws IOException {//模拟接收参数int id=1;//获取SqlsessionFactoryString resource = "mybatis-config.xml";InputStream inputStream = Resources.getResourceAsStream(resource);SqlSessionFactory sqlSessionFactory = new SqlSessionFactoryBuilder().build(inputStream);//获取Sqlsession对象SqlSession sqlSession = sqlSessionFactory.openSession();BrandMapper brandMapper = sqlSession.getMapper(BrandMapper.class);//执行方法Brand brand = new Brand();brand= brandMapper.selectById(id);System.out.println(brand);//释放资源sqlSession.close();}

总结：简单的用注解开发可以不用xml配置，但是复杂的业务还是需要用xml配置

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