动态SQL

    <select id="queryMessageList" resultMap="messageResult" parameterMap="messageParameter">
        SELECT id,command,description,content FROM message
        <where>
            <if test="command != null and !!&quot;&quot;.equals(command.trim())">
                AND command = #{command}
            </if>
            <if test="description != null and !&quot;&quot;.equals(description.trim())">
                AND description LIKE CONCAT('%', #{description}, '%')
            </if>
        </where>
    </select>

    <!--删除-->
    <delete id="deleteMessage" parameterType="int">
        DELETE FROM message WHERE id = #{_parameter}
    </delete>
    <delete id="deleteMessages" parameterType="java.util.List">
        DELETE FROM message WHERE id IN (
          <foreach collection="list" item="item" separator=",">
              #{item}
          </foreach>
        )
    </delete>

include的使用

    <sql id="messageColumns">
        id,command,description,content
    </sql>


    <!--查询-->
    <select id="queryMessageList" resultMap="messageResult" parameterMap="messageParameter">
        SELECT <include refid="messageColumns"/> FROM message
        <where>
            <if test="command != null and !!&quot;&quot;.equals(command.trim())">
                AND command = #{command}
            </if>
            <if test="description != null and !&quot;&quot;.equals(description.trim())">
                AND description LIKE CONCAT('%', #{description}, '%')
            </if>
        </where>
    </select>

一对多关系

package com.imooc.bean;

import java.util.List;

/**
 * 与指令表对应的实体类
 */
public class Command {
    /**
     * 主键
     */
    private String id;
    /**
     * 指令名称
     */
    private String name;
    /**
     * 描述
     */
    private String description;
    /**
     * 一条指令对应的自动回复内容列表
     */
    private List<CommandContent> contentList;
    ......
}

<?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="Command">
  <resultMap type="com.imooc.bean.Command" id="Command">
    <id column="C_ID" jdbcType="INTEGER" property="id"/>
    <result column="NAME" jdbcType="VARCHAR" property="name"/>
    <result column="DESCRIPTION" jdbcType="VARCHAR" property="description"/>
    <collection property="contentList"  resultMap="CommandContent.Content"/>
  </resultMap>
  
  <select id="queryCommandList" parameterType="com.imooc.bean.Command" resultMap="Command">
    select a.ID C_ID,a.NAME,a.DESCRIPTION,b.ID,b.CONTENT,b.COMMAND_ID
    from COMMAND a left join COMMAND_CONTENT b
    on a.ID=b.COMMAND_ID
    <where>
        <if test="name != null and !&quot;&quot;.equals(name.trim())">
            and a.NAME=#{name}
        </if>
        <if test="description != null and !&quot;&quot;.equals(description.trim())">
            and a.DESCRIPTION like '%' #{description} '%'
        </if>
    </where>
  </select>
</mapper>

<?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="CommandContent">
  <resultMap type="com.imooc.bean.CommandContent" id="Content">
    <id column="ID" jdbcType="INTEGER" property="id"/>
    <result column="CONTENT" jdbcType="VARCHAR" property="content"/>
    <result column="COMMAND_ID" jdbcType="VARCHAR" property="commandId"/>
  </resultMap>
</mapper>

其他常用标签

　　定义SQL语句　　　　　　insert、delete、update、select

　　配置java与结果集映射　　resultMap

　　控制SQL拼接　　　　　　foreach、if、choose

　　格式化输出　　　　　　　where、set、trim

　　配置关联关系　　　　　　collection、association

　　定义常量　　　　　　　　sql

　　引用常量　　　　　　　　include