Mybatis基础---------增删查改

增删改

1、新建工具类用来获取会话对象

import org.apache.ibatis.session.SqlSession;
import org.apache.ibatis.session.SqlSessionFactory;
import org.apache.ibatis.session.SqlSessionFactoryBuilder;
import org.apache.ibatis.io.Resources;import java.io.IOException;
import java.io.InputStream;/*** 静态变量：使用 static 关键字声明的变量是类级别的，所有实例共享相同的静态变量。这意味着无论创建多少个对象，它们都将共享相同的静态变量值。* public class MyClass {*     static int staticVar; // 静态变量，所有实例共享* }* 静态方法：使用 static 关键字声明的方法是类级别的，可以通过类名直接调用，无需实例化对象。这些方法通常用于执行与类本身相关的操作，而不是特定实例的操作。* public class MyClass {*     static void staticMethod() {*         // 静态方法*     }* }* 静态代码块：使用 static 关键字标识的代码块在类加载时执行，通常用于进行类级别的初始化操作。*/
public class SqlSessionUtil {static SqlSessionFactory sqlSessionFactory;static {try {InputStream inputStream = Resources.getResourceAsStream("mybatis-config.xml");sqlSessionFactory = new SqlSessionFactoryBuilder().build(inputStream);//加载输入流创建会话工厂} catch (IOException e) {e.printStackTrace();}}public  static SqlSession openSession(){return sqlSessionFactory.openSession();}}

2、加入junit依赖

<dependency><groupId>junit</groupId><artifactId>junit</artifactId><version>4.13.2</version><scope>test</scope>
</dependency>

3、通过映射传递属性

之前的sql语句全部写在了映射文件中，然而在实际应用时是通过映射传递属性的，也就是java对象对应sql语句中的占位符属性，属性名一般和java对象中的属性名相同，我们只需要用#{}作为占位符，占位符名称与java对象属性名一致即可。

如下实体类：

import java.util.Date;
public class User {private Integer id;private String username;private String password;private String salt;private String email;private int type;private int status;private String activationCode;private String headerUrl;private Date createTime;public int getId() {return id;}public void setId(int 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 getSalt() {return salt;}public void setSalt(String salt) {this.salt = salt;}public String getEmail() {return email;}public void setEmail(String email) {this.email = email;}public int getType() {return type;}public void setType(int type) {this.type = type;}public int getStatus() {return status;}public void setStatus(int status) {this.status = status;}public String getActivationCode() {return activationCode;}public void setActivationCode(String activationCode) {this.activationCode = activationCode;}public String getHeaderUrl() {return headerUrl;}public void setHeaderUrl(String headerUrl) {this.headerUrl = headerUrl;}public User(Integer id, String username, String password, String salt, String email, int type, int status, String activationCode, String headerUrl, Date createTime) {this.id = id;this.username = username;this.password = password;this.salt = salt;this.email = email;this.type = type;this.status = status;this.activationCode = activationCode;this.headerUrl = headerUrl;this.createTime = createTime;}public Date getCreateTime() {return createTime;}public void setCreateTime(Date createTime) {this.createTime = createTime;}
}

映射文件

<insert id="insertUser">INSERT INTO users (user_id, username, password, salt, email, type, status, activation_Code, header_url, create_time)
VALUES (null, #{username}, #{password}, #{salt}, #{email}, #{type}, #{status}, #{activationCode}, #{headerUrl}, #{createTime});
</insert>

测试：

@Test
public  void insertTest(){SqlSession sqlSession = SqlSessionUtil.openSession();User user = new User(null, "JohnDoe", "password", "salt123", "johndoe@example.com", 1, 1, "abcxyz", "https://example.com/image.jpg", new Date());//这里传入user实体,mybatis会自动将user属性值填充到sql语句中的占位符sqlSession.insert("insertUser",user);sqlSession.commit();sqlSession.close();//关闭会话
}

测试下修改和删除

<delete id="deleteUser">delete  from users where user_id=#{id};
</delete>
<update id="updateUser">UPDATE usersSET username = #{username},password = #{password},salt = #{salt},email = #{email},type = #{type},status = #{status},activation_Code = #{activationCode},header_Url = #{headerUrl},create_Time = #{createTime}WHERE user_id = #{id};
</update>

@Test//修改
public  void updateTest(){SqlSession sqlSession = SqlSessionUtil.openSession();User user = new User(2, "DDDD", "password", "salt123", "johndoe@example.com", 1, 1, "abcxyz", "https://example.com/image.jpg", new Date());sqlSession.insert("updateUser",user);sqlSession.commit();sqlSession.close();//关闭会话
}
@Test//删除
public  void deleteTest(){SqlSession sqlSession = SqlSessionUtil.openSession();sqlSession.insert("deleteUser",2);//当sql只有一个占位符时，传递的参数会直接赋值到该占位符中，与占位符名称无关sqlSession.commit();sqlSession.close();//关闭会话
}

查询

获取结果集，通过select标签中的resultType参数来指定查询结果封装到对应的实体类中，如果实体类中的属性与数据库表中属性不一致，可以使用as将对应数据库表中列名重命名并与实体类一致。

<select id="selectOneUser" resultType="User">select user_id as id, username, password, salt, email, type, status, activation_Code as activationCode, header_url as headerUrl, create_time as createTime from users where user_id=#{id};
</select>

或者采用另一种方式：通过在<resultMap> 中使用 <result> 标签来进行手动映射。

column--property==>数据库列名--实体类属性名

<resultMap id="userResultMap" type="User"><id property="id" column="user_id"/><result property="username" column="username"/><result property="password" column="password"/><result property="salt" column="salt"/><result property="email" column="email"/><result property="type" column="type"/><result property="status" column="status"/><result property="activationCode" column="activation_Code"/><result property="headerUrl" column="header_url"/><result property="create_time" column="createTime"/>
</resultMap>
<select id="selectUser" resultMap="userResultMap">select  * from users;
</select>

@Test
public void selectTest(){SqlSession sqlSession = SqlSessionUtil.openSession();List<User> selectUser = sqlSession.selectList("selectUser");for (User user : selectUser) {System.out.println(user.toString());}sqlSession.commit();sqlSession.close();//关闭会话
}