JavaEE 之 Mybatis

1.Mybatis

　　a.定义：MyBatis 是支持普通 SQL查询，存储过程和高级映射的优秀持久层框架

　　b.步骤：

　　　　①在src下创建 SqlMapConfig.xml 及 datasource.properties

　　　　②建UserMapper.java（相当于DAO）

public interface UserMapper {public int addUser(@Param("user")User user);public int delUserById(int userId);public int updateUser(@Param("user")User user);public User findUserById(int userId);public List<User> findAllUser();}

　　　　③建UserMapper.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="com.wode.mapper.UserMapper"><resultMap id="userMap" type="User"><id property="userId" column="user_id" /><result property="userName" column="user_name"/><result property="userPwd" column="user_pwd"/><result property="userType" column="user_type"/></resultMap><insert id="addUser"  parameterType="User">insert into users (user_id,user_name,user_pwd,user_type) values (null,#{user.userName},#{user.userPwd},#{user.userType})</insert><delete id="delUserById" parameterType="int">delete from users where user_id=#{userId}</delete><update id="updateUser" parameterType="User">update users set user_name = #{user.userName},user_pwd = #{user.userPwd},user_type = #{user.userType} where user_id = #{user.userId}</update><select id="findUserById" parameterType="int" resultMap="userMap">select * from users where user_id = #{user.userId}</select><select id="findAllUser" resultMap="userMap">select * from users</select></mapper>

　　　　④在Service中个使用

//一下代码可封装于另一个类中
InputStream  in = Resources.getResourceAsStream("SqlMapConfig.xml");
SqlSessionFactory sessionFactory = new SqlSessionFactoryBuilder().build(in);
SqlSession session = sessionFactory.openSession()//使用
UserMapper mapper=session.getMapper(UserMapper.class);//增
int result=mapper.addUser(user);
session.commit();//删
int result=mapper.delUserById(id);
session.commit();//改
int result=mapper.updateUser(user);
session.commit();//查单个对象
User user = mapper.findUserById(userId);//查所有对象
List<User> users = mapper.findAllUser()

2.其他查询

　　a.查询聚合函数

　　　　UserMapper.xml中

     <select id="findCountUser" resultType="int">select count(*) from users</select>

　　　　UserMapper.java中

public int findCountUser();

　　b.模糊查询

　　　　防止sql注入：

     <select id="findUserLikeName" parameterType="java.lang.String" resultMap="userMap">select * from users where user_name like concat('%',#{name},'%')</select>

　　　　不防止sql注入：

     <select id="findUserLikeName" parameterType="java.lang.String" resultMap="userMap">select * from users where user_name like '%${name}%'</select>

public List<User> findUserLikeName(@Param("name")String name);

　　c.查询单个字段

     <select id="findPwdByName" parameterType="java.lang.String" resultType="java.lang.String">select user_pwd from users where user_name = #{userName}</select>

    public String findPwdByName(@Param("userName")String userName);

3.一对一（One2One）

　　a.方法一：

　　　　UserMapper.xml中

    <resultMap id="userAndInfoMap" type="User"><id property="userId" column="user_id" /><result property="userName" column="user_name"/><result property="userPwd" column="user_pwd"/><result property="userType" column="user_type"/><association property="info" resultMap="com.wode.mapper.InfoMapper.InfoMapper"></association></resultMap><select id="findUserAndInfoById" parameterType="int" resultMap="userAndInfoMap">select * from users u left join infos i on u.user_id=i.user_id where u.user_id = #{userId}</select>

　　b.方法二

　　　　UserMapper.xml中

    <resultMap id="userAndInfoMap2" type="User"><id property="userId" column="user_id" /><result property="userName" column="user_name"/><result property="userPwd" column="user_pwd"/><result property="userType" column="user_type"/><association property="info" column="user_id" javaType="Info" select="com.wode.mapper.InfoMapper.findInfoByUserId"></association></resultMap><select id="findUserAndInfoById2" parameterType="int" resultMap="userAndInfoMap2">select * from users u where u.user_id = #{userId}</select>

　　　　InfoMapper.xml中

    <resultMap type="Info" id="InfoMapper"><id property="infoId" javaType="int" column="info_id" /><result javaType="java.lang.String" property="infoName" column="info_name" /><result javaType="java.lang.String" property="infoEmail" column="info_email" /></resultMap><select id="findInfoByUserId" resultMap="InfoMapper">select * from infos where user_id=#{userId}</select>

4.一对多（One2Many）

　　同One2One，仅在List<Info>部分将<association ...></association > 更换为<collection ...></collection>

5.多对多（Many2Many）

　　a.方法一：同上

    <resultMap id="UserAndCourseMapper2" type="User"><id property="userId" column="user_id" /><result property="userName" column="user_name"/><result property="userPwd" column="user_pwd"/><result property="userType" column="user_type"/><collection property="courses" resultMap="com.wode.mapper.CourseMapper.courseMap"></collection></resultMap><select id="findUserAndCourseById2" parameterType="Integer"resultMap="UserAndCourseMapper2">select * from users u,course c,user_course uc where u.user_id=uc.user_id and c.courseId = uc.course_id and u.user_id=#{userId}</select>

　　b.方法二：在通过userId查Course时需用到子查询（即第二个select）

    <resultMap id="UserAndCourseMapper" type="User"><id property="userId" column="user_id" /><result property="userName" column="user_name"/><result property="userPwd" column="user_pwd"/><result property="userType" column="user_type"/><collection property="courses" column="user_id" select="findCourseByUser"></collection></resultMap><select id="findUserAndCourseById" parameterType="Integer"resultMap="UserAndCourseMapper">select * from users where user_id=#{userId}</select><select id="findCourseByUser" parameterType="Integer"resultMap="com.wode.mapper.CourseMapper.courseMap">select * from course where courseId in(select course_id from user_course where user_id=#{userId})</select>

6.二级缓存

　　a.在SqlMapConfig.xml配置

<settings><setting name="cacheEnabled" value="true" />
</settings>

　　b.在UserMapper.xml中配置

<cache />

7.动态查询

　　a.if

    <select id="searchStudent" parameterType="java.util.Map"  resultMap="scoreMap">select * from score  where 1=1<if test="java!=null">and java &gt;=#{java}</if><if test="web!=null">and web &gt;=#{web}</if><if test="mysql!=null">and mysql &gt;=#{mysql}</if></select>

　　b.choose

    <select id="searchStudent2" parameterType="java.lang.String" resultMap="scoreMap">select * from score <choose> <when test="course=='java'">where java &gt;=60</when><when test="course=='web'">where web &gt;=60</when><otherwise>where mysql &gt;=60</otherwise></choose></select>

　　c.<where>

    <select id="searchStudent" parameterType="java.util.Map"  resultMap="scoreMap">select * from score <where><if test="java!=null">and java &gt;=#{java}</if><if test="web!=null">and web &gt;=#{web}</if><if test="mysql!=null">and mysql &gt;=#{mysql}</if></where></select>

　　d.trim

    <select id="searchStudent" parameterType="java.util.Map"  resultMap="scoreMap">select * from score   <trim prefix="where" prefixOverrides="and|or"><if test="java!=null">and java &gt;=#{java}</if><if test="web!=null">and web &gt;=#{web}</if><if test="mysql!=null">and mysql &gt;=#{mysql}</if></trim></select>

　　e.set

    <update id="updateScore" parameterType="java.util.Map">update score <set><if test="java != null">java = #{java},</if><if test="web != null">web = #{web},</if><if test="mysql != null">mysql = #{mysql}</if></set>where id = #{id}</update>

　　f.foreach

    <select id="findUser"  parameterType="java.util.Map" resultMap="userMap">select * from users<where>user_id in<foreach collection="usersId" item="userId" separator="," open="(" close=")" index="">#{userId}            </foreach></where></select>

8.注解

　　a.SqlMapConfig.xml中<mappers>只需配置

    <mappers><package name="com/wode/mapper" /></mappers>

　　b.普通注解

    //使用注解的方式新增用户@Insert("insert into users values(null,#{user.userName},#{user.userPwd},#{user.userType})")@Options(keyProperty="user.userId",useGeneratedKeys=true)public int addUser(@Param("user")User user);//注解的方式修改用户资料@Update("update users set user_name=#{name} where user_id=#{id}")public int updateUserNameById(@Param("name")String name,@Param("id")int id);//注解的方式删除用户@Delete("delete from users where user_id=#{id}")public int delById(@Param("id") int id);@Select("select * from users")
/**    @Results({@Result(id=true,property="userId",column="user_id",javaType=Integer.class),@Result(property="userName",column="user_name",javaType=String.class),@Result(property="userPwd",column="user_pwd",javaType=String.class),@Result(property="userType",column="user_type",javaType=Integer.class)})*/@ResultMap("userMap")public List<User> findAllUser();

　　c.一对多、多对一查询

    @Select("select * from users where user_id=#{id}")@Results({@Result(id=true,property="userId",column="user_id",javaType=Integer.class),@Result(property="userName",column="user_name",javaType=String.class),@Result(property="userPwd",column="user_pwd",javaType=String.class),@Result(property="userType",column="user_type",javaType=Integer.class),@Result(property="info",column="user_id",many=@Many(select="com.wode.mapper.UserInfoMapper.findByUser")) })@Select("select * from userInfo where info_id=#{infoId}")@Results({@Result(id=true,column="info_id",property="infoId",javaType=Integer.class),@Result(column="nickName",javaType=String.class,property="nickName"),@Result(column="email",property="email",javaType=String.class),@Result(column="user_id",property="user",one=@One(select="com.wode.mapper.UserMapper.findUserById"))})public UserInfo findInfoAndUser(@Param("infoId")int infoId);

9.其他

　　a.添加后返回主键

    <insert id="..." parameterType="..."><selectKey keyProperty="id" order="AFTER" resultType="java.lang.Integer">SELECT LAST_INSERT_ID()</selectKey>insert into ... (...) values (...)</insert>

　　b.有则修改，无则添加

    <insert id="addUserNum">insert into user_record (user_id, user_num) values (#{userId}, 1) ON DUPLICATE key UPDATE user_num = user_num+1</insert>

转载于:https://www.cnblogs.com/vettel0329/p/6735331.html

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