黑马Mybatis快速入门

创建user表，添加数据,Mysql:

 1 create database mybatis;
 2 use mybatis;
 3 drop table if exists tb_user;
 4 create table tb_user(
 5 id int primary key auto_increment,
 6 username varchar(20),
 7 password varchar(20),
 8 gender char(1),
 9 addr varchar(30)
10 );
11 INSERT INTO tb_user VALUES (1, 'zhangsan', '123', '男', '北京');
12 INSERT INTO tb_user VALUES (2, '李四', '234', '女', '天津');
13 INSERT INTO tb_user VALUES (3, '王五', '11', '男', '西安');

创建模块，导入坐标 在创建好的模块中的 pom.xml 配置文件中添加依赖的坐标:

<?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>

    <properties>
        <maven.compiler.source>17</maven.compiler.source>
        <maven.compiler.target>17</maven.compiler.target>
    </properties>

    <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>8.0.29</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>

编写 MyBatis 核心配置文件 -- > 替换连接信息 解决硬编码问题 在模块下的 resources 目录下创建mybatis的配置文件 mybatis-config.xml ，内容如下：

　　

<?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>
    <environments default="development">
        <environment id="development">
            <transactionManager type="JDBC"/>
            <dataSource type="POOLED">
                <property name="driver" value="com.mysql.cj.jdbc.Driver"/>
                <property name="url" value="jdbc:mysql:///mybatis?useSSL=false&amp;serverTimezone=UTC"/>
                <property name="username" value="root"/>

                <property name="password" value="1234"/>
            </dataSource>
        </environment>
    </environments>
    <mappers>
<!--  加载sql的映射文件 ,      -->
        <mapper resource="UserMapper.xml"/>
    </mappers>
</configuration>

编写 SQL 映射文件 --> 统一管理sql语句，解决硬编码问题 在模块的 resources 目录下创建映射配置文件 UserMapper.xml ，内容如下：

 1 <?xml version="1.0" encoding="UTF-8" ?>
 2 <!DOCTYPE mapper
 3         PUBLIC "-//mybatis.org//DTD Mapper 3.0//EN"
 4         "http://mybatis.org/dtd/mybatis-3-mapper.dtd">
 5 <!--
 6 namespace:名称空间
 7 -->
 8
 9 <mapper namespace="test">
10     <select id="selectAll" resultType="com.itheima.pojo.User">
11         select * from tb_user;
12     </select>
13 </mapper>

在 com.itheima.pojo 包下创建 User,在 com.itheima 包下编写 MybatisDemo 测试:

注意：mybatis-config.xml 文件 的 相关配置，如添加UTC和数据库账号密码，且pom.xml的数据库最好和已安装的数据库版本号相同，并且在idea左侧栏先连接上自己的数据库。

<property name="url" value="jdbc:mysql:///mybatis?useSSL=false&amp;serverTimezone=UTC"/>

<property name="username" value="root"/>

<property name="password" value="123456"/>

单个条件（动态SQL）

BrandMapper.xml: 其中where 标签 和 choose 标签 使得 动态搜索（查询条件可能不全）得以实现

<select id="selectByConditionSingle" resultMap="brandResultMap">
    select *
    from tb_brand
    <where>
        <choose>

            <when test="status != null">
                status = #{status}
            </when>

            <when test="companyName != null and  companyName != ''">
                company_name like #{companyName}
            </when>

            <when test="brandName != null and brandName != '' ">
                brand_name like #{brandName}
            </when>

        </choose>
    </where>
</select>

MybatisTest.java : 

 1     @Test
 2     public void testSelectByConditionSingle() throws IOException {
 3
 4         int status = 1;
 5         String companyName = "华为";
 6         String brandName = "华为";
 7
 8         companyName = "%" + companyName + "%";
 9         brandName =  "%" + brandName + "%";
10
11         Brand brand = new Brand();
12   //      brand.setStatus(status);
13    //   brand.setCompanyName(companyName);
14    //     brand.setBrandName(brandName);
15
16
17       //  Map map = new HashMap();
18         //map.put("status",status);
19         //  map.put("companyName",companyName);
20        // map.put("brandName",brandName);
21
22         String resource = "mybatis-config.xml";
23         InputStream inputStream = Resources.getResourceAsStream(resource);
24         SqlSessionFactory sqlSessionFactory = new SqlSessionFactoryBuilder().build(inputStream);
25
26         SqlSession sqlSession = sqlSessionFactory.openSession();
27
28         BrandMapper brandMapper = sqlSession.getMapper(BrandMapper.class);
29
30         // List<Brand> brands = brandMapper.selectByCondition(status, companyName, brandName);
31         // List<Brand> brands = brandMapper.selectByCondition(brand);
32
33
34         List<Brand> brands = brandMapper.selectByConditionSingle(brand);
35         System.out.println(brands);
36
37         sqlSession.close();
38
39
40     }