MyBatis 一对一配置、CURD操作

作者: ThingLin | 来源:发表于2017-02-25 20:29 被阅读387次

<a href="http://www.mybatis.org/mybatis-3/zh/index.html">MyBatis SQL Mapper Framework for Java</a>
　　<a href="http://ibatis.apache.org/">iBatis</a>

MyBatis 是支持定制化 SQL、存储过程以及高级映射的优秀的持久层框架。MyBatis 避免了几乎所有的 JDBC 代码和手动设置参数以及获取结果集。MyBatis 可以对配置和原生Map使用简单的 XML 或注解，将接口和 Java 的 POJOs(Plain Old Java Objects,普通的 Java对象)映射成数据库中的记录。

MyBatis与Hibernate同属于ORM解决方案之一，都是为了简化持久层的操作，它们都封装了JDBC。在效率上MyBatis高于Hibernate低于JDBC，MyBatis使用还是很简单的。

Demo<a href="http://download.csdn.net/detail/linjiqian/9764321"> http://download.csdn.net/detail/linjiqian/9764321</a>

引入MyBatis库

Paste_Image.png

MyBatis与Hibernate都是要配置实体和表的映射关系的配置文件，MyBatis的sql一般写在配置文件中，并且具有一定的动态性。

一个一对一的例子，建立学生表与班级表。，默认有三个班级。


-- create Database mybatisdb;

DROP TABLE student;
DROP TABLE classes;

-- 班级表
CREATE TABLE classes(
    cls_id INT(5) PRIMARY KEY,
    cls_name VARCHAR(10)    
);

-- 学生表
CREATE TABLE student(
    stu_id INT(5) PRIMARY KEY,
    stu_name VARCHAR(10),   
    cls_id INT(5),
    CONSTRAINT scid_fk FOREIGN KEY(cls_id) REFERENCES classes(cls_id)
);


-- 插入三个班级
INSERT INTO classes(cls_id,cls_NAME) VALUE(1,'乾坤大挪移');
INSERT INTO classes(cls_id,cls_NAME) VALUE(2,'降龙十八掌');
INSERT INTO classes(cls_id,cls_NAME) VALUE(3,'龟派气功');

Demo项目结构(idea开发)：

Paste_Image.png

班级实体：Classes.java


package cn.thinglin.demo.entity;

/**
 * Created by mac on 2017/2/25.
 */
public class Classes {

    private int id;
    private String name;

    public Classes(){}

    public Classes(int id, String name) {
        this.id = id;
        this.name = name;
    }

    public int getId() {
        return id;
    }

    public Classes setId(int id) {
        this.id = id;
        return this;
    }

    public String getName() {
        return name;
    }

    public void setName(String name) {
        this.name = name;
    }
}

班级实体配置：ClassesMapper.xml


<?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="classesNamespace">
    
    <resultMap type="cn.thinglin.demo.entity.Classes" id="classesMap">
        <id property="id" column="cls_id"/>
        <result property="name" column="cls_name"/>
    </resultMap>

</mapper>

学生实体：Student.java


package cn.thinglin.demo.entity;

/**
 * Created by mac on 2017/2/25.
 */
public class Student {

    private int id;
    private String name;
    private Classes classesId;

    public Student(){}

    public Student(int id, String name, Classes classesId) {
        this.id = id;
        this.name = name;
        this.classesId = classesId;
    }

    public int getId() {
        return id;
    }

    public void setId(int id) {
        this.id = id;
    }

    public String getName() {
        return name;
    }

    public void setName(String name) {
        this.name = name;
    }

    public Classes getClassesId() {
        return classesId;
    }

    public void setClassesId(Classes classesId) {
        this.classesId = classesId;
    }
}

学生实体配置：StudentMapper.xml


<?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">
<!-- 名称空间 -->
<mapper namespace="studentNamespace">

    <!-- 配置实体与表的映射 -->
    <resultMap type="cn.thinglin.demo.entity.Student" id="studentMap">
        <id property="id" column="stu_id"/>
        <result property="name" column="stu_name"/>
        <association property="classesId" resultMap="classesNamespace.classesMap"/> <!-- 1对1映射 -->
    </resultMap>

    <select id="findById" parameterType="string" resultMap="studentMap">
        select s.stu_id,s.stu_name,c.cls_name,c.cls_id
        from student s inner join classes c
        on s.cls_id = c.cls_id
        and s.stu_id = #{id}
    </select>

    <!-- 一般findAll查询所有不需要条件，这里是为说明可以设置这样的条件 -->
    <select id="findAll" parameterType="map" resultMap="studentMap">
        select * from student
        <!-- where开始设置条件 如果传进来的id不为null就设置条件表字段的id=传进来的id，这里可以动态设置条件也就是mybatis强大的动态sql -->
        <where>
            <if test="id!=null">
                and stu_id = #{id}
            </if>
            <if test="name!=null">
                and stu_name = #{name}
            </if>
            <if test="classesId!=null">
                and cls_id = #{classesId}
            </if>
        </where>
        <if test="index!=null">
            limit #{index},#{size}
        </if>
    </select>

    <!-- 判断数据实体的值，null?不增加这个字段:增加这个字段，所以if条件中写实体属性key，if结果写字段名 -->
    <sql id="key">
        <!-- trim suffixOverrides 去掉最后一个,号 -->
        <trim suffixOverrides=",">
            <if test="id!=null">
                stu_id,
            </if>
            <if test="name!=null">
                stu_name,
            </if>
            <if test="classesId!=null">
                cls_id,
            </if>
        </trim>
    </sql>

    <!-- 判断数据是否为空，不为空填上实体数据做为value -->
    <sql id="value">
        <trim suffixOverrides=",">
            <if test="id!=null">
                #{id},
            </if>
            <if test="name!=null">
                #{name},
            </if>
            <if test="classesId!=null">
                #{classesId.id}, <!-- 取的映射对象的id值 -->
            </if>
        </trim>
    </sql>

    <!-- <include refid="key"/>和<include refid="value"/>表示引用上面定义的sql片段 -->
    <insert id="add" parameterType="cn.thinglin.demo.entity.Student">
        insert into student(<include refid="key"/>) values(<include refid="value"/>)
    </insert>

    <!-- 更新 -->
    <update id="update" parameterType="cn.thinglin.demo.entity.Student">
        update student set stu_name = #{name},cls_id = #{classesId.id} where stu_id = #{id}
    </update>

    <!-- 删除 -->
    <delete id="delete" parameterType="cn.thinglin.demo.entity.Student">
        delete from student where stu_id = #{id}
    </delete>
    
</mapper>

MyBatis 总配置文件：mybatis.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>
    
    <!-- 加载数据库配置信息 -->
    <properties resource="db.properties"/>

    <!-- 设置一个默认的连接环境信息 -->
    <environments default="mysql_developer">

        <!-- 连接环境信息 先后设置了mysql_developer与oracle_developer，在environments的default属性指向要使用的那个 -->
        <environment id="mysql_developer">
            <!-- mybatis使用jdbc事务管理方式 -->
            <transactionManager type="jdbc"/>
            <!-- mybatis使用连接池方式来获取连接 -->
            <dataSource type="pooled">
                <!-- 配置与数据库交互的4个必要属性 -->
                <property name="driver" value="${mysql.driver}"/>
                <property name="url" value="${mysql.url}"/>
                <property name="username" value="${mysql.username}"/>
                <property name="password" value="${mysql.password}"/>
            </dataSource>
        </environment>

        
        <environment id="oracle_developer">
            <!-- mybatis使用jdbc事务管理方式 -->
            <transactionManager type="jdbc"/>
            <!-- mybatis使用连接池方式来获取连接 -->
            <dataSource type="pooled">
                <!-- 配置与数据库交互的4个必要属性 -->
                <property name="driver" value="${oracle.driver}"/>
                <property name="url" value="${oracle.url}"/>
                <property name="username" value="${oracle.username}"/>
                <property name="password" value="${oracle.password}"/>
            </dataSource>
        </environment>
    </environments>
    
    <!-- 加载实体映射文件-->
    <mappers>
        <mapper resource="cn/thinglin/demo/entity/StudentMapper.xml"/>
        <mapper resource="cn/thinglin/demo/entity/ClassesMapper.xml"/>
    </mappers>

</configuration>

MyBatis工具类：MyBatisUtil.java


package cn.thinglin.demo.util;

import java.io.IOException;
import java.io.Reader;
import org.apache.ibatis.io.Resources;
import org.apache.ibatis.session.SqlSession;
import org.apache.ibatis.session.SqlSessionFactory;
import org.apache.ibatis.session.SqlSessionFactoryBuilder;

/**
 * Created by mac on 2017/2/25.
 */
public class MyBatisUtil {
    private static ThreadLocal<SqlSession> threadLocal = new ThreadLocal<SqlSession>();
    private static SqlSessionFactory sqlSessionFactory;

    private MyBatisUtil(){}

    /**
     * 加载mybatis.xml配置文件
     */
    static{
        try {
            Reader reader = Resources.getResourceAsReader("mybatis.xml");
            sqlSessionFactory = new SqlSessionFactoryBuilder().build(reader);
        } catch (IOException e) {
            e.printStackTrace();
            throw new RuntimeException(e);
        }
    }

    /**
     * 获取SqlSession
     */
    public static SqlSession getSqlSession(){
        //从当前线程中获取SqlSession对象
        SqlSession sqlSession = threadLocal.get();
        //如果SqlSession对象为空
        if(sqlSession == null){
            //在SqlSessionFactory非空的情况下，获取SqlSession对象
            sqlSession = sqlSessionFactory.openSession();
            //将SqlSession对象与当前线程绑定在一起
            threadLocal.set(sqlSession);
        }
        //返回SqlSession对象
        return sqlSession;
    }

    /**
     * 关闭SqlSession与当前线程分开
     */
    public static void closeSqlSession(){
        //从当前线程中获取SqlSession对象
        SqlSession sqlSession = threadLocal.get();
        //如果SqlSession对象非空
        if(sqlSession != null){
            //关闭SqlSession对象
            sqlSession.close();
            //分开当前线程与SqlSession对象的关系，希望尽早回收内存
            threadLocal.remove();
        }
    }
}

持久层：StudentDao.java


package cn.thinglin.demo.dao;

import cn.thinglin.demo.entity.Student;
import cn.thinglin.demo.util.MyBatisUtil;
import org.apache.ibatis.session.SqlSession;

import java.util.Map;
import java.util.LinkedHashMap;
import java.util.List;

/**
 * Created by mac on 2017/2/25.
 */
public class StudentDao {

    /**
     * 根据id查找
     * @param id
     * @return
     * @throws Exception
     */
    public Student findById(int id) throws Exception{
        SqlSession sqlSession = null;
        try{
            sqlSession = MyBatisUtil.getSqlSession();
            return sqlSession.selectOne("studentNamespace.findById",id);
        }catch(Exception e){
            e.printStackTrace();
            throw e;
        }finally{
            MyBatisUtil.closeSqlSession();
        }
    }

    /**
     * 添加一个
     * @param student
     * @throws Exception
     */
    public void add(Student student) throws Exception{
        SqlSession sqlSession = null;
        try{
            sqlSession = MyBatisUtil.getSqlSession();
            sqlSession.insert("studentNamespace.add",student);
            sqlSession.commit();
        }catch(Exception e){
            e.printStackTrace();
            sqlSession.rollback();
            throw e;
        }finally{
            MyBatisUtil.closeSqlSession();
        }
    }

    /**
     * 查询所有符合条件的，并分页
     */
    public List<Student> findAll(Integer id,String name,Integer classesId,Integer index,Integer size){
        try{
            SqlSession sqlSession = MyBatisUtil.getSqlSession();

            Map<String,Object> map = new LinkedHashMap<String,Object>();
            map.put("id",id);
            map.put("name",name);
            map.put("classesId",classesId);
            map.put("index",index);
            map.put("size",size);

            return sqlSession.selectList("studentNamespace.findAll",map);
        }catch(Exception e){
            e.printStackTrace();
            throw e;
        }finally{
            MyBatisUtil.closeSqlSession();
        }
    }

    /**
     * 更新
     * @param stu
     */
    public void updateById(Student stu){
        SqlSession sqlSession = null;
        try{
            sqlSession = MyBatisUtil.getSqlSession();
            sqlSession.update("studentNamespace.update",stu);
            sqlSession.commit();
        }catch(Exception e){
            e.printStackTrace();
            sqlSession.rollback();
            throw e;
        }finally{
            MyBatisUtil.closeSqlSession();
        }
    }

    /**
     *删除
     * @param stu
     */
    public void deleteById(Student stu){
        SqlSession sqlSession = null;
        try{
            sqlSession = MyBatisUtil.getSqlSession();
            sqlSession.delete("studentNamespace.delete",stu);
            sqlSession.commit();
        }catch(Exception e){
            e.printStackTrace();
            sqlSession.rollback();
            throw e;
        }finally{
            MyBatisUtil.closeSqlSession();
        }
    }
}

测试：Test.java


package cn.thinglin.demo.test;

import cn.thinglin.demo.dao.StudentDao;
import cn.thinglin.demo.entity.Classes;
import cn.thinglin.demo.entity.Student;

/**
 * Created by mac on 2017/2/25.
 */
public class Test {

    public static void main(String[] args) {
        StudentDao dao = new StudentDao();
        try {
            //插入数据，三条cls_id =1 的
            dao.add(new Student(1, "大侠", new Classes(1, null)));
            dao.add(new Student(2, "大光头", new Classes(1, null)));
            dao.add(new Student(3, "过大年", new Classes(1, null)));
            dao.add(new Student(4, "活着", new Classes(2, null)));
            dao.add(new Student(5, "余华", new Classes(2, null)));

            System.out.println("分页查询：");
            System.out.println(dao.findAll(null,null,null,0,4).size()+"条数据");

            System.out.println("根据id查询：");
            Student student = dao.findById(2);
            System.out.println(student.getId()+" : "+student.getName() +" : " +student.getClassesId().getName() +" :cls_id = "+student.getClassesId().getId());
            //更新这条数据的cls_id
            student.setClassesId(student.getClassesId().setId(3));
            System.out.println(""+student.getId()+" :: "+student.getClassesId().getId() );
            dao.updateById(student);

            System.out.println("查询所有cls_id=1的：");
            System.out.println(dao.findAll(null,null,1,null,null).size()+"条数据");

            //删除
            dao.deleteById(student);

        } catch (Exception e) {
            e.printStackTrace();
        }
    }
}

demo_mybatis.gif

MyBatis 一对一配置、CURD操作

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