mybatis学习笔记(1):环境搭建与CRUD操作

1. 添加依赖

<dependency>
    <groupId>org.mybatisgroupId>
    <artifactId>mybatisartifactId>
    <version>3.4.1version>
dependency>

<dependency>
    <groupId>mysqlgroupId>
    <artifactId>mysql-connector-javaartifactId>
    <version>5.1.37version>
dependency>

主要添加下面这两个jar包:

目前还没有使用spring 进行整合所以这里就使用了这两个jar

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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 + "]";
    }
}

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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 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)

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4. 创建Mapper XML 文件

<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。

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5. 创建mybatis配置文件

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

<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>

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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 getAll(){
        SqlSessionFactory factory = MyBatisUtil.getFactory();
        SqlSession session = factory.openSession();
        EmployeeMapper mapper = session.getMapper(EmployeeMapper.class);
        List 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()

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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

<mappers>
        
        
        
         <mapper class="com.mybatis.mapper.EmployeeMapper"/>
    mappers>

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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