Mybatis学习笔记
之前看过Mybatis，但因为时间长远没有用，大部分已经忘记了，这里贴下coding练习过程
1. 导包
- log4j.jar
- mybatis-3.4.6.jar
- mysql-connector-java-5.1.39-bin.jar
2. 准备配置
2.1 log4j.xml
<?xml version="1.0" encoding="UTF-8" ?>
<!DOCTYPE log4j:configuration SYSTEM "log4j.dtd">
<log4j:configuration xmlns:log4j="http://jakarta.apache.org/log4j/">
<appender name="STDOUT" class="org.apache.log4j.ConsoleAppender">
<param name="Encoding" value="UTF-8" />
<layout class="org.apache.log4j.PatternLayout">
<param name="ConversionPattern" value="%-5p %d{MM-dd HH:mm:ss,SSS} %m (%F:%L) \n" />
</layout>
</appender>
<logger name="java.sql">
<level value="debug" />
</logger>
<logger name="org.apache.ibatis">
<level value="info" />
</logger>
<root>
<level value="debug" />
<appender-ref ref="STDOUT" />
</root>
</log4j:configuration>2.2 db.properties
jdbc.driver = com.mysql.jdbc.Driver
jdbc.url = jdbc\:mysql\://127.0.0.1\:3306/mybatis?useUnicode\=true&characterEncoding\=UTF-8&serverTimezone\=Asia/Shanghai&useAffectedRows\=true
jdbc.username = root
jdbc.password =2.3 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">
<!-- 根标签 -->
<configuration>
<!-- 引入外部java资源文件properties,mybatis自带 -->
<properties resource="db.properties"></properties>
<!-- 最好显示写上，防止版本更新默认值不同 -->
<settings>
<setting name="mapUnderscoreToCamelCase" value="true"/>
<setting name="useActualParamName" value="true"/>
<setting name="lazyLoadingEnabled" value="true"/>
<setting name="aggressiveLazyLoading" value="false"/>
</settings>
<!-- 别名，存在的意义仅在于用来减少类完全限定名的冗余 -->
<typeAliases>
<!-- alias可选，默认小写 -->
<typeAlias alias="User" type="com.howl.entity.User"/>
<!-- 自动扫描包，包下的类自动使用Bean的首字母小写 -->
<package name="com.howl.entity"/>
</typeAliases>
<!-- 环境，可以配置多个，default：缺省，和spring整合后environments将废除 -->
<environments default="development">
<!-- id：唯一标识，下面两个标签必须有 -->
<environment id="development">
<!-- 事务管理器，JDBC类型的事务管理器 -->
<transactionManager type="JDBC" />
<!-- 数据源，池类型的数据源 -->
<dataSource type="POOLED">
<property name="driver" value="${jdbc.driver}" />
<property name="url" value="${jdbc.url}" />
<property name="username" value="${jdbc.username}" />
<property name="password" value="${jdbc.password}" />
</dataSource>
</environment>
<environment id="product">
<transactionManager type="JDBC"></transactionManager>
<dataSource type="POOLED">
<property name="driver" value="${jdbc.driver}"/>
<property name="url" value="${jdbc.url}"/>
<property name="username" value="${jdbc.username}"/>
<property name="password" value="${jdbc.password}"/>
</dataSource>
</environment>
</environments>
<!-- 引入映射文件或接口 ，可以使用类名，包名(针对接口)、相对路径‘/’（针对xml文件） -->
<mappers>
<mapper resource="mybatis/mappers/UserMapper.xml"/>
<mapper resource="mybatis/mappers/CategoryMapper.xml"/>
<!-- 引入接口,这样的话找不到映射文件，只能把映射文件和接口放在同一包下 -->
<!-- <mapper class="com.howl.mapper.dao.UserMapper" /> -->
<!-- 还可以在接口上使用注解开发，这样就省去了映射文件，但只适用于简单查询，且耦合度高 -->
<!-- 批量注册,映射文件要和接口在同一包下 -->
<!-- <package name="com.howl.dao"/> -->
</mappers>
</configuration>3. 创建表和实体
3.1 表
CREATE TABLE `user` (
`user_id` int(11) NOT NULL AUTO_INCREMENT,
`user_name` varchar(255) DEFAULT NULL,
`user_email` varchar(255) DEFAULT NULL,
`user_category_id` int(11) DEFAULT NULL,
PRIMARY KEY (`user_id`)
) ENGINE=InnoDB AUTO_INCREMENT=31 DEFAULT CHARSET=utf8;CREATE TABLE `category` (
`category_id` int(11) NOT NULL,
`category_name` varchar(255) DEFAULT NULL,
PRIMARY KEY (`category_id`)
) ENGINE=InnoDB DEFAULT CHARSET=utf8;3.2 entity
package com.howl.entity;
public class User {
private int id;
private String name;
private String email;
private int category_id;
private Category category;
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 String getEmail() {
return email;
}
public void setEmail(String email) {
this.email = email;
}
public int getCategory_id() {
return category_id;
}
public void setCategory_id(int category_id) {
this.category_id = category_id;
}
public Category getCategory() {
return category;
}
public void setCategory(Category category) {
this.category = category;
}
public User() {
super();
}
public User(String name, String email) {
super();
this.name = name;
this.email = email;
}
public User(int id, String name) {
super();
this.id = id;
this.name = name;
}
public User(int id, String name, String email) {
super();
this.id = id;
this.name = name;
this.email = email;
}
@Override
public String toString() {
return "User [id=" + id + ", name=" + name + ", email=" + email + ", category_id=" + category_id + ", category="
+ category + "]";
}
}package com.howl.entity;
import java.util.List;
public class Category {
private int id;
private String name;
private List<User> users;
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 List<User> getUsers() {
return users;
}
public void setUsers(List<User> users) {
this.users = users;
}
@Override
public String toString() {
return "Category [id=" + id + ", name=" + name + ", users=" + users + "]";
}
}4. 创建表与实体的映射文件及与关联全局配置文件
<?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.howl.dao.UserMapper">
<!-- 结果映射，用于字段与属性不一致 -->
<!-- 可选方法@Param、resultMap、语句查询时用as -->
<resultMap type="com.howl.entity.User" id="UserMap">
<id property="id" column="user_id"/>
<result property="name" column="user_name"/>
<result property="email" column="user_email"/>
<!-- 一对一，联合查询（嵌套）,这里懒不在全局配置里写别名了,这种查询需要在写sql语句时全部查出 -->
<association property="category" javaType="com.howl.entity.Category">
<id property="id" column="category_id"/>
<result property="name" column="category_name"/>
</association>
<!-- 分步关联查询,用写好的语句来查询，传入外层已经查到的数据作为参数 -->
<!-- column是外层插好的值的名字 -->
<!-- 厉害于可以延迟加载，所以分布加载存在的必要性，不然分两次查询网络传输都损耗性能 -->
<!-- 懒加载在需要用到的时候，比如syso输出时再发请求 -->
<!-- 多值传参进写好的语句时：column="{key1=column1,key2=column2}" -->
<association property="category" select="com.howl.dao.CategoryMapper.selectCategoryById" column="user_category_id" fetchType="eager/lazy">
</association>
</resultMap>
<select id="selectUserById" resultMap="UserMap">
SELECT * FROM user WHERE user_id = #{id};
</select>
<!-- 单参用封装User类，框架通过getter来获取 -->
<select id="selectUserByConditions" resultMap="UserMap">
SELECT * FROM user WHERE user_id = #{id} AND user_name = #{name};
</select>
<!-- 返回集合，结果类型也要写集合中元素的类型，模糊查询 -->
<select id="selectUserByLikeName" resultMap="UserMap">
SELECT * FROM user WHERE user_name LIKE #{name}
</select>
<!-- 一对一关联查询 -->
<select id="selectUserByIdWithCategory" resultMap="UserMap">
SELECT * FROM user u, category c WHERE u.user_category_id = c.category_id AND u.user_id = #{id}
</select>
<!-- 动态语句 -->
<select id="selectUserDynamic" resultMap="UserMap">
<!-- 绑定处理，不推荐 -->
<!-- <bind name="nameLike" value=" '%' + name + '%' "/> -->
SELECT * FROM user WHERE 1 = 1
<if test="name != null and name != '' ">
AND user_name LIKE #{name}
</if>
<if test="email != null and email != '' ">
AND user_email LIKE #{email}
</if>
<if test="category_id != null and category_id != '' ">
AND user_category_id = #{category_id}
</if>
</select>
<!-- 动态语句 -->
<!-- 批处理 -->
<select id="selectUserByIdForeach" resultMap="UserMap">
SELECT * FROM user WHERE user_id IN
<foreach collection="list" item="user_id" separator="," open="(" close=")">
#{user_id}
</foreach>
</select>
<!-- 批处理 -->
<!-- 增删改 -->
<!-- 参数类型可选，类型转换器会帮你判断 -->
<!-- 获取自增主键 -->
<insert id="insertUser" parameterType="User" useGeneratedKeys="true" keyProperty="id">
INSERT INTO user(`user_name`,`user_email`) VALUES (#{name},#{email});
</insert>
<update id="updateUser">
UPDATE user SET user_name = #{name},user_email = #{email} WHERE user_id = #{id}
</update>
<delete id="deleteUser">
DELETE FROM user WHERE user_id = #{id}
</delete>
<!-- 增删改 -->
</mapper>public interface UserMapper {
public User selectUserById(int id);
public User selectUserByConditions(User user);
// 多参传入方法
public User selectUserByConditions(Map map);
public User selectUserByConditions(@Param("id")int id, @Param("name")String name);
public User selectUserByIdWithCategory(@Param("id")int id);
public List<User> selectUserByLikeName(String name);
// 动态查询
public List<User> selectUserDynamic(User user);
// 批处理
public List<User> selectUserByIdForeach(List list);
public int insertUser(User user);
public int updateUser(User user);
public int deleteUser(int id);
}<?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.howl.dao.CategoryMapper">
<resultMap type="com.howl.entity.Category" id="CategoryMap">
<id property="id" column="category_id"/>
<result property="name" column="category_name"/>
<!-- 一对多，联合查询,ofType指定集合元素的类型 -->
<collection property="users" ofType="com.howl.entity.User">
<id property="id" column="user_id"/>
<result property="name" column="user_name"/>
<result property="email" column="user_email"/>
</collection>
</resultMap>
<select id="selectCategoryById" resultMap="CategoryMap">
SELECT * FROM category WHERE category_id = #{id};
</select>
<select id="selectCategoryByIdWithUser" resultMap="CategoryMap">
SELECT * FROM category c LEFT JOIN user u on c.category_id = u.user_category_id WHERE category_id = #{id}
</select>
</mapper>public interface CategoryMapper {
public Category selectCategoryById(int id);
public Category selectCategoryByIdWithUser(int id);
}5. 工具类
public class MybatisUtil {
private static InputStream in;
private static SqlSessionFactory sqlSessionFactory;
static {
try {
String resource = "mybatis-config.xml";
in = Resources.getResourceAsStream(resource);
} catch (IOException e) {
e.printStackTrace();
}
}
private MybatisUtil(){}
// 可选数据源
public static SqlSession getSqlSession (String environment){
sqlSessionFactory = new SqlSessionFactoryBuilder().build(in,environment);
return sqlSessionFactory.openSession();
}
public static void closeSqlSession(SqlSession sqlSession){
if(sqlSession != null){
sqlSession.close();
}
}
// 测试连接
public static void main(String[] args) {
Connection conn = MybatisUtil.getSqlSession("product").getConnection();
if(conn != null){
System.out.println("连接成功");
}
}
}6. 测试
public class main {
public static void main(String[] args) {
// 工具类获取SqlSession连接会话
SqlSession sqlSession = MybatisUtil.getSqlSession("product");
// 根据会话获取代理对象
UserMapper userMapper = sqlSession.getMapper(com.howl.dao.UserMapper.class);
// 增
User user1 = new User("Howl","1210911104@qq.com");
userMapper.insertUser(user1);
System.out.println("自增主键为:" + user1.getId());
sqlSession.commit();
// 删
int deleteNum = userMapper.deleteUser(24);
System.out.println("删除影响条数为：" + deleteNum);
sqlSession.commit();
// 改(多次同样修改也返回1，应为返回的是matched的数，需要在连接url上加参数useAffectedRows=true)
int updateNum = userMapper.updateUser(new User(26,"Howlet","111111"));
System.out.println("修改的影响条数为：" + updateNum);
sqlSession.commit();
// 单参查询
User user2 = userMapper.selectUserById(25);
System.out.println("查询结果为：" + user2.getName());
// 单参数查询，封装成User了
User user3 = new User(26,"Howl");
user3 = userMapper.selectUserByConditions(user3);
System.out.println(user3);
// 模糊查询记住要在传参时拼接，语句中不支持，除非用绑定
List<User> users1 = userMapper.selectUserByLikeName("%How%");
for(User value : users1){
System.out.println(value);
}
// 一对一联合查询
User user4 = userMapper.selectUserByIdWithCategory(25);
System.out.println(user4);
// 动态模糊查询，建议把模糊字段在sql语句外拼接
User user5 = new User();
user5.setName("%ho%");
// user5.setCategory_id(1);
List<User> users = userMapper.selectUserDynamic(user5);
for(User value : users){
System.out.println(value);
}
// 批处理,更新也是如此返回影响条数 ，一般前端都是传数组的
List<Integer> list1 = new ArrayList();
list1.add(25);
list1.add(26);
list1.add(27);
List<User> list2 = userMapper.selectUserByIdForeach(list1);
for(User value : list2){
System.out.println(value);
}
// 懒查询,开启association的select
// user查询语句和正常查询user一样，不同于之处在于调用关联对象后，框架调用select片段
User user6 = userMapper.selectUserById(25);
System.out.println("查询结果为：" + user6.getName());
try {
Thread.sleep(2000);
} catch (InterruptedException e) {
e.printStackTrace();
}
System.out.println(user6.getCategory());
//-------------------------- category -----------------------------
// 根据会话获取
CategoryMapper categoryMapper = sqlSession.getMapper(com.howl.dao.CategoryMapper.class);
Category category1 = categoryMapper.selectCategoryById(1);
System.out.println(category1);
Category category2 = categoryMapper.selectCategoryByIdWithUser(1);
System.out.println(category2.getName());
}
}7. 补充
- Mybatis中的事务是默认开启的，因此我们在完成操作以后，需要我们手动去提交事务！
- Dao接口里的方法，是不能重载的，因为是全限名+方法名的保存和寻找策略
- Dao接口的工作原理是JDK动态代理，Mybatis运行时会使用JDK动态代理为Dao接口生成代理proxy对象，代理对象proxy会拦截接口方法，转而执行MappedStatement所代表的sql，然后将sql执行结果返回
- MyBatis 包含一个名叫 Resources 的工具类，它包含一些实用方法，可使从 classpath 或其他位置加载资源文件更加容易
#{}实际上就是调用了类的getter方法- @Alias("User")，放在entity上，mybatis别名注解
- 框架实现了1.8的新时间API映射
- 分页
分页插件的基本原理是使用Mybatis提供的插件接口，实现自定义插件，在插件的拦截方法内拦截待执行的sql，然后重写sql，根据dialect方言，添加对应的物理分页语句和物理分页参数
举例：`select * from student，拦截sql后重写为：select t.* from （select * from student）t limit 0，10`- mybatis处理参数
单个参数：不会做特殊处理，不管写什么直接映射进去，可用基本类型，也可传pojo 多个参数时：会特殊处理，将多参数处理成map,#{}就是从map集合中获取指定的key，所以获取的时候会有提示 `Parameter 'id' not found. Available parameters are [arg1, arg0, param1, param2]` 默认--即参数可写arg1，arg2,arg3.....,或者param1,param2,param3....，现在的版本已经不用索引了，看版本把 map封装--在传参的时候明确写出参数名字，因为mybatis对参数是做map封装处理的 @param注解--key:@param注解来指定的值，#{指定的key}，取出参数值，注解放在接口的方法的形参中 使用TO--来封装传输对象 pojo封装--属性是在pojo内部所有的 注意：如果传参是Collection、List或者数组，则不能用arg1，param1，使用的时候需要#{list[0]}、#{array[0]}，因为mybatis会自动封装，多此一举？ #{}和${}, #只能用于条件参数位置中的位置，而$能用于拼接任何地方的，比如下面只能用${} SELECT * FROM ${} ;
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原始发表：2020-02-22 ，如有侵权请联系 cloudcommunity@tencent.com 删除
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