[我的日记] 【成都校区】mybatis学习笔记

【mybatis-04】

01 mybatis 延迟加载/懒加载 (需要时才进行加载)
00 开启mybatis的延迟加载
<settings>

<setting name="lazyLoadingEnabled" value="true"/>

<setting name="aggressiveLazyLoading" value="false"/>
</settings>

01 association 实现懒加载
List<Account> findAllLazyInit();

<select id="findAllLazyInit" resultMap="account_user_lazy_init_map">
select
*
from account
</select>

<resultMap id="account_user_lazy_init_map" type="account">
<id column="id" property="id"></id>
<result column="uid" property="uid"></result>
<result column="money" property="money"></result>
<association property="user" column="uid" javaType="user" select="com.mybatis.dao.UserDao.findById"></association>
</resultMap>

User findById(Integer id);

<select id="findById" parameterType="java.lang.Integer" resultType="com.mybatis.domain.User" useCache="true">
select * from user
where id = #{id}
</select>

02 collection 实现懒加载
List<User> findAllLazyInit();

<select id="findAllLazyInit" resultMap="user_account_lazy_init_map">
select * from user
</select>

<resultMap id="user_account_lazy_init_map" type="user">
<id property="id" column="id"></id>
<result property="username" column="username"></result>
<result property="birthday" column="birthday"></result>
<result property="sex" column="sex"></result>
<result property="address" column="address"></result>
<collection property="accountList" ofType="account" column="id" select="com.mybatis.dao.AccountDao.findByUserId"></collection>
</resultMap>

List<Account> findByUserId(Long uid);

<select id="findByUserId" parameterType="long" resultType="account">
select * from account where uid = #{uid}
</select>

02 mybatis 一级缓存 sqlSession
只要 SqlSession 没有 clearCache 或 close，它就存在。
当调用 SqlSession 的修改，添加，删除，commit()，close()，clearCache()方法时，将清空一级缓存

测试：在同一个 sqlSession 中获取同一个id，返回的地址相同

03 mybatis 二级缓存 sqlSessionFactory
01  配置二级缓存的开启
<settings>

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

02 配置相应的 Mapper 映射文件
<mapper namespace="com.itheima.dao.IUserDao">

<cache></cache>
</mapper>

03 配置 statement 的 useCache 属性

<select id="findById" resultType="user" parameterType="int" useCache="true">
select * from user where id = #{uid}
</select>
【注意】针对每次查询都需要最新的数据 sql，要设置成 useCache=false，禁用二级缓存

04 测试：
在不同的 sqlSession 中获取同一个id
只发出一条 sql ,但返回的地址不同
因为二级缓存，保存的是数据

05 注意
缓存的类需要实现 java.io.Serializable 接口

04 mybatis 注解开发
00 常用注解说明
@Insert:实现新增
@Update:实现更新
@Delete:实现删除
@Select:实现查询
@Result:实现结果集封装
@Results:可以与@Result 一起使用，封装多个结果集
@ResultMap:实现引用@Results 定义的封装
@One:实现一对一结果集封装
@Many:实现一对多结果集封装
@SelectProvider: 实现动态 SQL 映射
@CacheNamespace:实现注解二级缓存的使用

01  CRUD
@Select("select * from user")
List<User> findAll();

@Select("select * from user  where id=#{id} ")
User findById(Integer id);

@SelectKey(keyProperty = "id",keyColumn = "id",resultType = int.class,before = false,statement = "select last_insert_id()")
@Insert("insert into user(username,address,sex,birthday)values(#{username},#{address},#{sex},#{birthday})")
void save(User user);

@Update("update user set username=#{username},sex=#{sex},birthday=#{birthday},address=#{address} where id=#{id}")
void update(User user);

@Delete("delete from user where id=#{id} ")
void deleteById(Integer id);

@Select("select * from user  where id=#{id} ")
User findById(Integer id);

@Select("select * from user where username like concat('%',#{username},'%') ")
// @Select("select * from user where username like '%${value}%' ")
List<User> findByName(String username);

02 复杂关系映射
01 @Many collection
/**
   * 包含 account 信息
   * @return
   */
@Select("select * from user")
@Results(id="userMap",value={
@Result(id=true,column = "id",property = "id"),
@Result(column = "username",property = "username"),
@Result(column = "address",property = "address"),
@Result(column = "sex",property = "sex"),
@Result(column = "birthday",property = "birthday"),
@Result(property = "accountList",column = "id",javaType = List.class,
many = @Many(select = "com.mybatis.dao.AccountDao.findByUserId",fetchType = FetchType.LAZY))
})
List<User> findAllVersion2();

@Select("select * from account where uid = #{uid}")
List<Account> findByUserId(Long uid);

02 @One association
/**
   *
   * @return
   */
@Select("select * from account")
@Results(id = "account_user_map",value = {
@Result(property = "uid",column = "uid"),
@Result(property = "user",column = "uid",javaType = User.class,
one = @One(select = "com.mybatis.dao.UserDao.findById",fetchType = FetchType.EAGER)
)
})
List<Account> findAllVersion2();

@Select("select * from user  where id=#{id} ")
User findById(Integer id);

05 dao查询使用多个参数
@Select("select * from user where username like concat('%',#{username},'%') and sex = #{sex} ")
List<User> findByUsernameAndSex(@Param("username") String username,@Param("sex") String sex);

06 注解二级缓存
<settings>

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

@CacheNamespace(blocking=true)
public interface IUserDao {}

【mybatis-03】

01 mybatis  连接池分类
01 UNPOOLED 不使用连接池的数据源
02 POOLED 使用连接池的数据源
03 JNDI 使用jndi实现的数据源

02 事务控制
01 jdbc 事务控制默认自动提交 setAutoCommmit(false),开启手动提交

02 mybatis 事务控制
      01 openSession() 默认手动提交
02 openSession(autoCommit)

03 动态SQL
01 if
      <select id="findByCondition" resultMap="userMap">
select * from user
where 1=1
<if test="username != null"></if>
and username like #{username}
</select>

02 choose(when otherwise)

03 trim(where set)
<select id="findByUser" resultType="user" parameterType="user">
select * from user
<where>
<if test="username!=null and username != '' ">
and username like #{username}
</if>
<if test="address != null">
and address like #{address}
</if>
</where>
</select>

04 foreach
<select id="findUserByIds" resultMap="userMap" parameterType="QueryVO">
select * from user
<where>
<if test="ids!=null and ids.size()>0">
<foreach collection="ids" open="id in (" separator="," close=")" item="tmpId" >
#{tmpId}
</foreach>
</if>
</where>
</select>

04 简化编写 sql 语句
<sql id="defaultSql">
select * from user
</sql>

<select id="findAll" resultType="user">
<include refid="defaultSql"></include>
</select>

05 mybatis 一对多/多对一
user (1:m) account
01 一对一/多对一
01 AccountUser 包含sql查询出来的全部字段
02 Account (属性 user)

<resultMap id="accountResultMap" type="account">
<id column="aid" property="id"></id>
<result column="uid" property="uid"></result>
<result column="money" property="money"></result>

<association property="user" javaType="user">
<id column="id" property="id"></id>
<result column="username" property="username"></result>
<result column="sex" property="sex"></result>
<result column="birthday" property="birthday"/>
<result column="address" property="address"/>
</association>
</resultMap>

<select id="findAllVersion2" resultMap="accountResultMap">
select
a.id as aid ,a.uid,a.money,
u.id,u.username,u.sex,u.birthday,u.address
from account a
inner join user u
on a.uid = u.id
</select>

01 一对多
User (属性 List<Account> accountList)

<resultMap id="userMap" type="com.mybatis.domain.User">
<id property="id" column="id"></id>
<result property="username" column="username"></result>
<result property="birthday" column="birthday"></result>
<result property="sex" column="sex"></result>
<result property="address" column="address"></result>

<collection property="accountList" ofType="account">
<id column="aid" property="id"></id>
<result column="uid" property="uid"></result>
<result column="money" property="money"></result>
</collection>
</resultMap>

<select id="findAllVersion2" resultMap="userMap">
select
a.id as aid ,a.uid,a.money,
u.id,u.username,u.sex,u.birthday,u.address
from user u
left join account a
on a.uid = u.id
</select>

06 mybatis 多对多
user (m:n) role

<resultMap id="roleResultMap" type="role">
<id property="roleId" column="rid"/>
<result property="roleName" column="role_name"/>
<result property="roleDesc" column="role_desc"/>
<collection property="userList" ofType="user">
<id property="id" column="id"></id>
<result property="username" column="username"></result>
<result property="birthday" column="birthday"></result>
<result property="sex" column="sex"></result>
<result property="address" column="address"></result>
</collection>
</resultMap>

<select id="findAll" resultMap="roleResultMap">
select
u.*,r.id as rid,r.role_name,r.role_desc
from role r
left join user_role ur on r.id = ur.rid
left join user u on u.id = ur.uid
</select>

【mybatis-02】

01 基于代理dao 实现 CRUD
01 select

User findById(Integer id);

<select id="findById" parameterType="java.lang.Integer" resultType="com.mybatis.domain.User">
      select * from user
      where id = #{id}
</select>

02 insert

【需要 sqlSession.commit(),openSession()事务默认不提交】

void save(User user);

<insert id="save" parameterType="com.mybatis.domain.User">
      
      <selectKey keyProperty="id" keyColumn="id" resultType="int" order="AFTER">
         select last_insert_id();
      </selectKey>
      insert into user
      (username,birthday,sex,address)
      values
      (#{username},#{birthday},#{sex},#{address})
</insert>

03 update
【需要 sqlSession.commit(),openSession()事务默认不提交】

void update(User user);

<update id="update" parameterType="com.mybatis.domain.User">
      UPDATE USER
      set username = #{username},
      birthday = #{birthday},
      sex = #{sex},
      address = #{userAddress}
      where id = #{id}
</update>

04 delete
【需要 sqlSession.commit(),openSession()事务默认不提交】

void deleteById(Integer id);

<delete id="deleteById" parameterType="java.lang.Integer">
      DELETE FROM user where id = #{uid}
</delete>

02 小插曲 ognl  apache 提供的一种表达式语言

Object Graphic Navigation Language 对象图导航语言

按照一定的语法格式来获取数据的对象.属性名

03 模糊查询

   /**
   * 根据姓名进行模糊查询
   * @param username
   * @return
   */
List<User> findByName(String username);

01 方式一 #{username} 【preparedStatement,推荐】

<select id="findByName" parameterType="java.lang.String" resultType="com.mybatis.domain.User">
      select * from user
      where username like  #{username}【】
</select>

List<User> userList = userDao.findByName("%王%");【】

02 方式二 ${username} 【statement,不大推荐，使用字符串拼接】

<select id="findByName" parameterType="java.lang.String" resultType="com.mybatis.domain.User">
      select * from user
      where username like  '%${value}%'【写法固定】
</select>

List<User> userList = userDao.findByName("王");【】

04 聚合函数查询

Integer findTotal();

<select id="findTotal" resultType="java.lang.Integer">
      select count(*) from user
</select>

05 parameterType
别名，参考 TypeAliasRegistery.class 或官方文档

06 resultType
mysql 在 window 下，不区分大小写

07 数据库列名与实体的属性名对应不上【】
01 查询的时候，取别名，使得别名与属性名对应
select name(列名) as username(属性名)

02 使用 resultMap

<resultMap id="userMap" type="com.mybatis.domain.User">

      <id property="id" column="id"></id>
      <result property="username" column="username"></result>
      <result property="birthday" column="birthday"></result>
      <result property="sex" column="sex"></result>
      <result property="address" column="address"></result>

      
      <collection property="accountList" ofType="account">
         <id column="aid" property="id"></id>
         <result column="uid" property="uid"></result>
         <result column="money" property="money"></result>
      </collection>
</resultMap>

<select id="findAll" resultMap="userMap">
select * from user
</select>

08 mybatis 传统dao开发(了解)
01 dao
02 daoImpl
03 sqlSession api

【mybatis-01】

01 mybatis 介绍

01 持久层框架
02 内部封装了jdbc
03 开发者只需要关注 sql

04 ORM 思想解决实体与数据库映射的问题

02 mybatis 入门（基于xml）

01 引入依赖
01 mybatis
02 junit
03 mysql-connector-java
04 log4j

02 实体类

03 dao接口

04 映射文件 xxxDao.xml
【】xml约束从文件中拷贝

05 sqlMapConfig.xml 配置文件
【】xml约束从文件中拷贝

06 测试类
01 读取配置文件
02 sqlSessionFactoryBuilder
03 sqlSessionFactory
04 sqlSession
05 userDao = sqlSession.getMapper(UserDao.class)
06 调用方法
      【】如果是增加、更新、删除，需要使用 sqlSession.commit()
07 释放资源

03 基于注解

01 删除 xxxDao.xml
02 在接口的方法上使用注解

@Select("select * from user")
List<User> findAll();

03 sqlMapConfig.xml 修改

<mappers>
      <mapper class="com.mybatis.dao.UserDao"/>
</mappers>

04 自定义mybatis框架

01 涉及的知识点
工厂模式
构建者模式
代理模式
反射
自定义注解
注解的反射
xml解析
数据库元数据
元数据的反射

02 引入的依赖
01 log4j
02 dom4j
03 jaxen
04 mysql-connector-java
05 junit

03 工具类
01 XMLConfigBuilder
      dom4j+xpath
      解析主配置文件，将配置信息设置到 defaultSqlSession
02 Executor
      负责执行 sql 语句，封装结果集
03  DatasourceUtil
      数据源的工具类
04 Resources
      读取配置文件
05 Mapper
      用于封装查询时的必要信息（sql + 实体类的类名全路径）
06 Configuration
      01 数据库信息 driver、url、username、password
      02 sql 的 map 集合 <String,Mapper>

实体类、dao接口、xxxDao.xml

07 SqlSessionFactoryBuilder
      根据 inputSream ，创建 SqlSessionFactory
08 SqlSessionFactory DefaultSqlSessionFactory
      创建 SqlSession
09 SqlSession DefaultSqlSession
10 MapperProxyFactory
      使用动态代理，增强方法

11 @Select
      自定义注解

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[我的日记] 【成都校区】mybatis学习笔记

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