Mybatis学习笔记(idea)

Mybatis（ieda）

一款优秀的持久层框架
官网：Mybatis-3官网

Maven仓库：

<dependency>
    <groupId>org.mybatis</groupId>
    <artifactId>mybatis</artifactId>
    <version>3.5.3</version>
</dependency>

数据库：

CREATE TABLE `user`(
`id`  INT(20) NOT NULL PRIMARY KEY,
`name`  VARCHAR(30) DEFAULT  NULL,
`pwd` VARCHAR(30) DEFAULT NULL
)ENGINE=INNODB CHARSET=utf8;

INSERT INTO `user`(`id`,`name`,`pwd`) VALUES
(1,'lix','123456'),
(2,'admin','123456'),
(3,'root','123456')

导入依赖

<!--导入依赖 -->
    <dependencies>
        <!--mysql-->
        <dependency>
            <groupId>mysql</groupId>
            <artifactId>mysql-connector-java</artifactId>
            <version>8.0.21</version>
        </dependency>
        <!--mybatis-->
        <dependency>
            <groupId>org.mybatis</groupId>
            <artifactId>mybatis</artifactId>
            <version>3.5.5</version>
        </dependency>
        <!--junit-->
        <dependency>
            <groupId>junit</groupId>
            <artifactId>junit</artifactId>
            <version>4.13</version>
            <scope>test</scope>
        </dependency>
    </dependencies>

编写mybatis配置文件-----表头：

<?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>
  <environments default="development">
    <environment id="development">
      <transactionManager type="JDBC"/>
      <dataSource type="POOLED">
        <property name="driver" value="${driver}"/>
        <property name="url" value="${url}"/>
        <property name="username" value="${username}"/>
        <property name="password" value="${password}"/>
      </dataSource>
    </environment>
  </environments>
  <mappers>
    <mapper resource="org/mybatis/example/BlogMapper.xml"/>
  </mappers>
</configuration>

获得sqlsessionfactory

private static SqlSessionFactory sqlSessionFactory;

    static{
        try {
            //获得sqlsessionFactory
            String resource = "org/mybatis/example/mybatis-config.xml";
            InputStream inputStream = Resources.getResourceAsStream(resource);
            SqlSessionFactory sqlSessionFactory = new SqlSessionFactoryBuilder().build(inputStream);
        } catch (Exception e) {
            e.printStackTrace();
        }
    }

    public static SqlSession getSqlSession(){
        return sqlSessionFactory.openSession();
    }

Mapper.xml表头：

<?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="org.mybatis.example.BlogMapper">
  <select id="selectBlog" resultType="Blog">
    select * from Blog where id = #{id}
  </select>
</mapper>

报错：

Could not find resource org/mybatis/example/mybatis-config.xml

解决：纯配置文件路径错误，检查路径即可

报错：

org.apache.ibatis.builder.BuilderException: Error parsing SQL Mapper Configuration. Cause: java.io.IOException: Could not find resource

解决：在pom.xml中加入以下配置

<build>
        <resources>
            <resource>
                <directory>src/main/resources</directory>
                <includes>
                    <include>**/*.properties</include>
                    <include>**/*.xml</include>
                </includes>
                <filtering>true</filtering>
            </resource>
            <resource>
                <directory>src/main/resources</directory>
                <includes>
                    <include>**/*.properties</include>
                    <include>**/*.xml</include>
                </includes>
                <filtering>true</filtering>
            </resource>
        </resources>
    </build>

log4j配置文件

#将等级为DEBUG的日志信息输出到console和file这两个目的地，console和file的定义在下面的代码
log4j.rootLogger=DEBUG,console,file

#控制台输出的相关设置
log4j.appender.console = org.apache.log4j.ConsoleAppender
log4j.appender.console.Target = System.out
log4j.appender.console.Threshold = Debug
log4j.appender.console.layout = org.apache.log4j.PatternLayout
log4j.appender.console.layout.ConversionPattern = [%c]-%m%n

#文件输出的相关设置
log4j.appender.file = org.apache.log4j.RollingFileAppender
log4j.appender.file.File = ./log/lix.log
log4j.appender.file.MaxFileSize = 10mb
log4j.appender.file.Threshold = DEBUG
log4j.appender.file.layout = org.apache.log4j.PatternLayout
log4j.appender.file.layout.ConversionPattern = [%p][%d{yy-mm-dd}][%c]%m%n

#日志输出级别
log4j.logger.org.mybatis = DEBUG
log4j.logger.java.sql = DEBUG
log4j.logger.java.sql.Statement = DEBUG
log4j.logger.java.sql.ResultSet = DEBUG
log4j.logger.java.sql.PreparedStatement = DEBUG

二.注解CRUD

package com.lix.dao;

import com.lix.pojo.User;
import org.apache.ibatis.annotations.*;

import java.util.HashMap;
import java.util.List;
import java.util.Map;

/**
 * program mybatis-01
 * @author lix
 */
public interface UserMapper {
    /**
     * getUsers
     * @return
     */
    @Select("select * from user")
    List<User> getUsers();

    /**
     *
     * getUserById
     * @param id
     * @param name
     * @return
     * 方法存在多个参数，
     */
    @Select("select * from user where id=#{id}")
    User getUserById(@Param("id") int id, @Param("name") String name);
    /**
     * addUser
     * @param map
     * @return
     */
    @Insert("insert into user(id,name,pwd) values(#{id},#{name},#{pwd})")
    int addUser(Map<String,Object> map);

    /**
     * updateUser
     * @param map
     * @return
     */
    @Update("update user set name = #{name},pwd=#{pwd} where id = #{id}")
    int updateUser(Map<String,Object> map);

    /**
     * deleteUse
     * @param id
     * @return
     */
    @Delete("delete from user where id = #{id}")
    int deleteUse(@Param("id") int id);


}

【注意：我们必须要把核心配置类（UserMapper.java）绑定到核心配置文件中（mybatis-config.xml）】

关于@Param()注解
- 基本类型的参数或者String类型，需要加
- 引用类型不需要加
- 如果只有一个基本类型的话，可以忽略，建议加
- 我们在SQL中引用的就是我们这里的的@Param()中设定的属性名
{} 可以很大程度的防止sql注入 ${}
Lombok
- Project Lombok is a java library that automatically plugs into your editor and build tools, spicing up your java.
  Never write another getter or equals method again, with one annotation your class has a fully featured builder, Automate your logging variables, and much more.
  - Project Lombok是一个java库，它可以自动插入到你的编辑器和构建工具中，为您的java注入新的活力。
    
    不要再编写其他getter或equals方法，有了一个注释，类就有了功能齐全的构建器、自动化日志变量等等。
- ```
package com.lix.dao;

import lombok.AllArgsConstructor;
import lombok.Data;
import lombok.NoArgsConstructor;

/**
 * program mybatis-02
 * @author lix
 * description 加在类上所有属性都加，加在属性上，只有属性加
 */
@Data
@AllArgsConstructor
@NoArgsConstructor
public class User {
    private int id;
    private String name;
    private String pwd;

}
```
多对一，一对多处理

4.1 多对一

4.2 一对多

多个学生，对应一个老师
学生：关联--多个学生关联一个老师（多对一）
老师：集合--一个老师有很多学生（一对多）

4.1、按照查询嵌套处理

<select id="getStudent" resultMap="StudentTeacher">
    select * from student
</select>
<resultMap id="StudentTeacher" type="Student">
    <result column="id" property="id"/>
    <result column="name" property="name"/>
    <!--复杂属性单独处理
                对象：association
                集合：collection
            -->
    <association property="teacher" column="tid" javaType="Teacher" select="getTeacher"/>
    <collection property=""/>
</resultMap>
<select id="getTeacher" resultType="Teacher">
    select * from teacher where id = #{tid};
</select>

4.2、按照结果嵌套处理

<select id="getStudent2" resultMap="StudentTeacher2">
    select s.id sid,s.name sname,t.name tname
    from student s,teacher t
    where s.id = t.id
</select>
<resultMap id="StudentTeacher2" type="Student">
    <result column="sid" property="id"/>
    <result column="sname" property="name"/>
    <!--复杂属性单独处理
            对象：association
            集合：collection
        -->
    <association property="teacher" javaType="Teacher">
        <result column="tname" property="name"/>
    </association>
    <collection property=""/>
</resultMap>

三.动态SQL

<select id="iii" resultType="sss">
        select * from mybatis.user
        <where>
            <if test="title != null">
                title =1
            </if>
        </where>
        <set></set>
    </select>

四.缓存

【先走二级缓存-----》再看一级缓存-------》最后在数据库中查找

posted @ 2020-10-22 11:32 六爻呈乾阅读(129) 评论(1) 收藏举报

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只要做了，那就最少有一半的胜算嘛

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Mybatis学习笔记(idea)

Mybatis（ieda）

二.注解CRUD

{} 可以很大程度的防止sql注入 ${}

三.动态SQL

四.缓存

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