mybatis学习笔记(1):环境搭建与CRUD操作

系统管理员 2022-05-21 04:22 144阅读 0赞

## 1. 添加依赖 ##

<dependency>
        <groupId>org.mybatis</groupId>
        <artifactId>mybatis</artifactId>
        <version>3.4.1</version>
    </dependency>
    
    <dependency>
        <groupId>mysql</groupId>
        <artifactId>mysql-connector-java</artifactId>
        <version>5.1.37</version>
    </dependency>

主要添加下面这两个jar包:  
![这里写图片描述][70]  
目前还没有使用spring 进行整合所以这里就使用了这两个jar

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

## 2. 实体类Employee ##

package com.mybatis.domian;
    
    public class Employee { 
    
        private Integer id;
        private String lastName;
        private String gender;
        private String email;
    
        public Employee() {
            super();
        }
        public Employee(Integer id, String lastName, String gender, String email) {
            super();
            this.id = id;
            this.lastName = lastName;
            this.gender = gender;
            this.email = email;
        }
        public Integer getId() {
            return id;
        }
        public void setId(Integer id) {
            this.id = id;
        }
        public String getLastName() {
            return lastName;
        }
        public void setLastName(String lastName) {
            this.lastName = lastName;
        }
        public String getGender() {
            return gender;
        }
        public void setGender(String gender) {
            this.gender = gender;
        }
        public String getEmail() {
            return email;
        }
        public void setEmail(String email) {
            this.email = email;
        }
        @Override
        public String toString() {
            return "Employee [id=" + id + ", lastName=" + lastName + ", gender="
                    + gender + ", email=" + email + "]";
        }
    }

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

## 3. 接口文件EmployeeMapper ##

package com.mybatis.mapper;
    
    import java.util.List;
    
    import com.mybatis.domian.Employee;
    
    public interface EmployeeMapper { 
    
        public Employee getEmpById(Integer id);
    
        public Integer addEmp(Employee emp);
    
        public Integer updateEmp(Employee emp);
    
        public boolean deleteEmp(Integer id);
    
        public List<Employee> getAll();
    }

对于增删改操作，mybatis会自动获取更改的数据条数，也可以是是否值(更改了为true,没有更改为false)

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

## 4. 创建Mapper XML 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.mybatis.mapper.EmployeeMapper">
        
        <select id="getEmpById" resultType="com.mybatis.domian.Employee">
            select * from tbl_employee where id = #{id}
        </select>
    
        <insert id="addEmp" parameterType="com.mybatis.domian.Employee">
            insert into tbl_employee(last_name,gender,email) values(#{lastName},#{gender},#{email})
        </insert>
    
        <update id="updateEmp" parameterType="com.mybatis.domian.Employee">
            update tbl_employee set last_name = #{lastName} where id=#{id}
        </update>
    
        <delete id="deleteEmp" parameterType="Integer">
            delete from tbl_employee where id=#{id}
        </delete>
        
        <select id="getAll" resultType="com.mybatis.domian.Employee">
            select * from tbl_employee
        </select>
    </mapper>

>  *  这个文件的编写是程序员主要的工作，也是mybatis的精髓所在，手动编写sql语句。
>  *  namespace为当前文件的唯一标识，一般指定为一个接口文件如EmployeeMapper .java文件。
>  *  里面的内容可以看作接口文件每个方法的实现(数据库操作)，id对应了方法名。
>  *  select需要指定结果类型，其他的需要指定参数类型。

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

## 5. 创建mybatis配置文件 ##

在类路径下创建mybatis配置文件 mybatis-config.xml :

<?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>
        
        <properties resource="db.properties"></properties>
        
        <settings>
            
            <setting name="mapUnderscoreToCamelCase" value="true"/>
            
        </settings>
        
        <environments default="dev">
            
            <environment id="dev">
                
                <transactionManager type="JDBC" />
                <dataSource type="POOLED">
                    <property name="driver" value="${dev_driver}" />
                    <property name="url" value="${dev_url}" />
                    <property name="username" value="${dev_username}" />
                    <property name="password" value="${dev_password}" />
                </dataSource>
            </environment>
            
            <environment id="pro">
                <transactionManager type="JDBC" />
                <dataSource type="POOLED">
                    <property name="driver" value="${prod_driver}" />
                    <property name="url" value="${prod_url}" />
                    <property name="username" value="${prod_username}" />
                    <property name="password" value="${prod_password}" />
                </dataSource>
            </environment>
        </environments>
        <mappers>
            
            
            
             <mapper class="com.mybatis.mapper.EmployeeMapper"/>
        </mappers>
    </configuration>

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

## 6. 写一个工具类来获取SqlSessionFactory ##

public class MyBatisUtil {
        public static SqlSessionFactory getFactory(){
            String resource = "mybatis-config.xml";
            //加载 mybatis 的配置文件（它也加载关联的映射文件）
            Reader reader = null;
            try {
                reader = Resources.getResourceAsReader(resource);
            } catch (IOException e) {
                // TODO Auto-generated catch block
                e.printStackTrace();
            }
            //构建 sqlSession 的工厂
            SqlSessionFactory sessionFactory = new SqlSessionFactoryBuilder().build(reader);
            return sessionFactory;
        }
    }

## 7. 编写dao ##

public class EmployeeDao {
    
        public Employee getEmpById(Integer id){
            SqlSessionFactory factory = MyBatisUtil.getFactory();
            SqlSession session = factory.openSession();
            EmployeeMapper mapper = session.getMapper(EmployeeMapper.class);
            Employee empById = mapper.getEmpById(id);
            return empById;
        };
    
        public Integer addEmp(Employee emp){
            SqlSessionFactory factory = MyBatisUtil.getFactory();
            SqlSession session = factory.openSession();
            EmployeeMapper mapper = session.getMapper(EmployeeMapper.class);
            Integer result = mapper.addEmp(emp);
            session.commit();
            session.close();
            return result;
        };
    
        public Integer updateEmp(Employee emp){
            SqlSessionFactory factory = MyBatisUtil.getFactory();
            SqlSession session = factory.openSession();
            EmployeeMapper mapper = session.getMapper(EmployeeMapper.class);
            Integer result = mapper.updateEmp(emp);
            session.commit();
            session.close();
            return result;
        };
    
        public boolean deleteEmp(Integer id){
            SqlSessionFactory factory = MyBatisUtil.getFactory();
            SqlSession session = factory.openSession();
            EmployeeMapper mapper = session.getMapper(EmployeeMapper.class);
            boolean result = mapper.deleteEmp(id);
            session.commit();
            session.close();
            return result;
        };
    
        public List<Employee> getAll(){
            SqlSessionFactory factory = MyBatisUtil.getFactory();
            SqlSession session = factory.openSession();
            EmployeeMapper mapper = session.getMapper(EmployeeMapper.class);
            List<Employee> result = mapper.getAll();
            session.commit();
            session.close();
            return result;
        };
    }

>  *  这里使用session.getMapper(EmployeeMapper.class) 获取一个代理类，这个代理类是将Mapper xml文件和接口类结合生成的文件。这样我们调用接口方法时节可以指定我们自定义的sql语句了。
>  *  session.commit()，非查询操作才能起作用。如果不想手动提交，可以使用SqlSession session = factory.openSession(true);，这样可以自动提交 session使用完，记得close()

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

## 使用注解的方式 ##

@Insert("insert into tbl_employee(last_name,gender,email) values(#{
       lastName},#{
       gender},#{
       email})")
    public Integer insert(Employee emp);

*  直接在接口方法上写sql，这样就不用在Mapper xml文件中配置了，但是这种方式违背了mybatis的初衷，不建议这样使用。
 *  对于简单的数据库操作，而且不频繁修改的数据库操作可以这样使用。

注意：对于Mapper文件别忘记在mybatis-config.xml 文件中注册

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

## 总结 ##

使用myBatis的准备步骤：  
1. 配置mybatis-config.xml文件  
2. 配置Mapper XML文件（定义接口）  
3. 获取SqlSessionFactory  
4. 通过SqlSessionFactory得到SqlSession  
5. 通过session.getMapper(xx.class) 得到代理对象  
6. 调用得到的代理对象的方法操作数据库  
7. 提交关闭session

[70]: /images/20220521/59349de1577e4c39bc7c969b3190872e.png