Mybatis与mysql一对多映射,以及java类编写

其他 2021-01-22 20:01:20 阅读次数: 0

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文章目录

前言

因为懒惰,在一个查询中,一个表被联查了两次,提供一种不需要再业务层进行二次调用的方式。

提示：以下是本篇文章正文内容，下面案例可供参考

一、Mybatis是什么？

各位"看官"移步官网啦!! https://mybatis.org/mybatis-3/zh/index.html。

二、使用步骤

忘记上表了,在这里插一下

部门表:
在这里插入图片描述

项目表:
在这里插入图片描述
项目阶段表:
在这里插入图片描述

1.方式一代码如下

1.1Java类 1->n(1对多,1对1)

public class Project extends BaseEntity{
    
    
    private static final long serialVersionUID = 1L;

    private Long projectId;

    /** 项目名称 */
    @Excel(name = "项目名称")
    private String projectName;

    /** 所属部门id */
    @Excel(name = "所属部门id")
    private Long deptId;

    private Long constrDeptId;

    /** 所属部门*/
    private Dept dept;

    private Dept constructionTeam;

    /**项目阶段*/
    private List<ProjectStage> projectStages = new ArrayList<>();

    /** -1:未开始,0:已开始,1:已结束 */
    @Excel(name = "-1:未开始,0:已开始,1:已结束")
    private String status;

    /** 计划开始时间 */
    @JsonFormat(pattern = "yyyy-MM-dd")
    @Excel(name = "计划开始时间", width = 30, dateFormat = "yyyy-MM-dd")
    private Date planStartTime;

    /** 实际开始时间 */
    @JsonFormat(pattern = "yyyy-MM-dd")
    @Excel(name = "实际开始时间", width = 30, dateFormat = "yyyy-MM-dd")
    private Date actualStartTime;

    /** 计划结束时间 */
    @JsonFormat(pattern = "yyyy-MM-dd")
    @Excel(name = "计划结束时间", width = 30, dateFormat = "yyyy-MM-dd")
    private Date planEndTime;

    /** 实际结束时间 */
    @JsonFormat(pattern = "yyyy-MM-dd")
    @Excel(name = "实际结束时间", width = 30, dateFormat = "yyyy-MM-dd")
    private Date actualEndTime;
   
}

1.1.1重点标注

在这里插入图片描述

1.2 xml代码

<?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.project.mapper.ProjectMapper">
    
    <resultMap type="com.project.model.Project" id="ProjectResult">
        <result property="projectId"    column="project_id"    />
        <result property="projectName"    column="project_name"    />
        <result property="deptId"    column="dept_id"    />
        <result property="constrDeptId"    column="constr_dept_id"    />
        <result property="status"    column="status"    />
        <result property="planStartTime"    column="plan_start_time"    />
        <result property="actualStartTime"    column="actual_start_time"    />
        <result property="planEndTime"    column="plan_end_time"    />
        <result property="actualEndTime"    column="actual_end_time"    />
        <result property="delFlag"    column="del_flag"    />
        <result property="createBy"    column="create_by"    />
        <result property="createTime"    column="create_time"    />
        <result property="updateBy"    column="update_by"    />
        <result property="updateTime"    column="update_time"    />
        <result property="remark"    column="remark"    />
        <association property="dept" column="dept_id" javaType="com.project.model.Project" resultMap="DeptResult1"/>
        <association property="constructionTeam" column="constr_dept_id" javaType="com.project.model.Project" resultMap="DeptResult2"/>
        <collection property="projectStages" javaType="java.util.List" resultMap="ProjectStageResult"/>
    </resultMap>
    <resultMap type="com.soldier.model.Dept" id="DeptResult1">
        <result property="deptId"    column="dept_id"    />
        <result property="parentId"    column="parent_id"    />
        <result property="ancestors"    column="ancestors"    />
        <result property="deptName"    column="dept_name"    />
        <result property="orderNum"    column="order_num"    />
        <result property="leader"    column="leader"    />
        <result property="phone"    column="phone"    />
        <result property="email"    column="email"    />
        <result property="status"    column="status"    />
    </resultMap>
    <resultMap type="com.soldier.model.Dept" id="DeptResult2">
        <result property="deptId"    column="team_dept_id"    />
        <result property="parentId"    column="team_parent_id"    />
        <result property="ancestors"    column="team_ancestors"    />
        <result property="deptName"    column="team_dept_name"    />
        <result property="orderNum"    column="team_order_num"    />
        <result property="leader"    column="team_leader"    />
        <result property="phone"    column="team_phone"    />
        <result property="email"    column="team_email"    />
        <result property="status"    column="team_status"    />
    </resultMap>
    <resultMap type="com.project.model.ProjectStage" id="ProjectStageResult">
        <result property="proStageId"    column="pro_stage_id"    />
        <result property="proStageName"    column="pro_stage_name"    />
        <result property="projectId"    column="project_id"    />
        <result property="constrDeptId"    column="constr_dept_id"    />
        <result property="status"    column="status"    />
<!--        <result property="planStartTime"    column="plan_start_time"    />
        <result property="actualStartTime"    column="actual_start_time"    />
        <result property="planEndTime"    column="plan_end_time"    />
        <result property="actualEndTime"    column="actual_end_time"    />-->
    </resultMap>

    <sql id="selectProjectVo">
        select project_id, project_name, dept_id, constr_dept_id, status, plan_start_time, actual_start_time, plan_end_time, actual_end_time, del_flag, create_by, create_time, update_by, update_time, remark from _project
    </sql>

    <sql id="selectProjectVo2">
        select project_id, project_name, dept_id, constr_dept_id, status, plan_start_time,
        actual_start_time, plan_end_time, actual_end_time, del_flag, create_by, create_time,
        update_by, update_time, remark,
        d.dept_name,ur.dept_name as team_dept_name,r.pro_stage_name,r.pro_stage_name,r.constr_dept_id
        from _project 
        left join _dept d on dept_id = d.dept_id
        left join _dept ur on constr_dept_id = ur.dept_id
        left join _project_stage r on project_id = r.project_id
    </sql>

    <select id="selectProjectList" parameterType="com.project.model.Project" resultMap="ProjectResult">
        <include refid="selectProjectVo2"/>
        <where>  
            <if test="projectName != null  and projectName != ''"> and project_name like concat('%', #{projectName}, '%')</if>
            <if test="deptId != null "> and dept_id = #{deptId}</if>
            <if test="constrDeptId != null "> and constr_dept_id = #{constrDeptId}</if>
            <if test="status != null  and status != ''"> and status = #{status}</if>
            <if test="planStartTime != null "> and plan_start_time = #{planStartTime}</if>
            <if test="actualStartTime != null "> and actual_start_time = #{actualStartTime}</if>
            <if test="planEndTime != null "> and plan_end_time = #{planEndTime}</if>
            <if test="actualEndTime != null "> and actual_end_time = #{actualEndTime}</if>
        </where>
    </select>
    
    <select id="selectProjectById" parameterType="Long" resultMap="ProjectResult">
        <include refid="selectProjectVo"/>
        where project_id = #{projectId}
    </select>
        
    <insert id="insertProject" parameterType="com.project.model.Project">
        insert into _project
        <trim prefix="(" suffix=")" suffixOverrides=",">
            <if test="projectId != null">project_id,</if>
            <if test="projectName != null">project_name,</if>
            <if test="deptId != null">dept_id,</if>
            <if test="constrDeptId != null">constr_dept_id,</if>
            <if test="status != null">status,</if>
            <if test="planStartTime != null">plan_start_time,</if>
            <if test="actualStartTime != null">actual_start_time,</if>
            <if test="planEndTime != null">plan_end_time,</if>
            <if test="actualEndTime != null">actual_end_time,</if>
            <if test="delFlag != null">del_flag,</if>
            <if test="createBy != null">create_by,</if>
            <if test="createTime != null">create_time,</if>
            <if test="updateBy != null">update_by,</if>
            <if test="updateTime != null">update_time,</if>
            <if test="remark != null">remark,</if>
         </trim>
        <trim prefix="values (" suffix=")" suffixOverrides=",">
            <if test="projectId != null">#{projectId},</if>
            <if test="projectName != null">#{projectName},</if>
            <if test="deptId != null">#{deptId},</if>
            <if test="constrDeptId != null">#{constrDeptId},</if>
            <if test="status != null">#{status},</if>
            <if test="planStartTime != null">#{planStartTime},</if>
            <if test="actualStartTime != null">#{actualStartTime},</if>
            <if test="planEndTime != null">#{planEndTime},</if>
            <if test="actualEndTime != null">#{actualEndTime},</if>
            <if test="delFlag != null">#{delFlag},</if>
            <if test="createBy != null">#{createBy},</if>
            <if test="createTime != null">#{createTime},</if>
            <if test="updateBy != null">#{updateBy},</if>
            <if test="updateTime != null">#{updateTime},</if>
            <if test="remark != null">#{remark},</if>
         </trim>
    </insert>

    <update id="updateProject" parameterType="com.project.model.Project">
        update _project
        <trim prefix="SET" suffixOverrides=",">
            <if test="projectName != null">project_name = #{projectName},</if>
            <if test="deptId != null">dept_id = #{deptId},</if>
            <if test="constrDeptId != null">constr_dept_id = #{constrDeptId},</if>
            <if test="status != null">status = #{status},</if>
            <if test="planStartTime != null">plan_start_time = #{planStartTime},</if>
            <if test="actualStartTime != null">actual_start_time = #{actualStartTime},</if>
            <if test="planEndTime != null">plan_end_time = #{planEndTime},</if>
            <if test="actualEndTime != null">actual_end_time = #{actualEndTime},</if>
            <if test="delFlag != null">del_flag = #{delFlag},</if>
            <if test="createBy != null">create_by = #{createBy},</if>
            <if test="createTime != null">create_time = #{createTime},</if>
            <if test="updateBy != null">update_by = #{updateBy},</if>
            <if test="updateTime != null">update_time = #{updateTime},</if>
            <if test="remark != null">remark = #{remark},</if>
        </trim>
        where project_id = #{projectId}
    </update>

    <delete id="deleteProjectById" parameterType="Long">
        delete from _project where project_id = #{projectId}
    </delete>

    <delete id="deleteProjectByIds" parameterType="String">
        delete from _project where project_id in 
        <foreach item="projectId" collection="array" open="(" separator="," close=")">
            #{projectId}
        </foreach>
    </delete>
    
</mapper>

1.2.1重点标注

在这里插入图片描述

在这里插入图片描述在这里插入图片描述
在这里插入图片描述

要将你所需要的字段清楚的写出来,并且名相同&&值不同的字段要起别名;

如果你只想要某个表的name/特殊字段,不想用对象封装,也可以用这种方式:

2.方式二代码如下:

代码如下（示例）：

2.1java:

public class Project extends BaseEntity{
    
    
    private static final long serialVersionUID = 1L;

    /** $column.columnComment */
    private Long projectId;

    /** 项目名称 */
    @Excel(name = "项目名称")
    private String projectName;

    /** 所属部门id */
    @Excel(name = "所属部门id")
    private Long deptId;

    private Long constrDeptId;

    private String deptName;
    private String teamDeptName;

    /** 所属部门*/
    private Dept dept;

    private Dept constructionTeam;

    /**项目阶段*/
    private List<ProjectStage> projectStages = new ArrayList<>();

    /** -1:未开始,0:已开始,1:已结束 */
    @Excel(name = "-1:未开始,0:已开始,1:已结束")
    private String status;

    /** 计划开始时间 */
    @JsonFormat(pattern = "yyyy-MM-dd")
    @Excel(name = "计划开始时间", width = 30, dateFormat = "yyyy-MM-dd")
    private Date planStartTime;

    /** 实际开始时间 */
    @JsonFormat(pattern = "yyyy-MM-dd")
    @Excel(name = "实际开始时间", width = 30, dateFormat = "yyyy-MM-dd")
    private Date actualStartTime;

    /** 计划结束时间 */
    @JsonFormat(pattern = "yyyy-MM-dd")
    @Excel(name = "计划结束时间", width = 30, dateFormat = "yyyy-MM-dd")
    private Date planEndTime;

    /** 实际结束时间 */
    @JsonFormat(pattern = "yyyy-MM-dd")
    @Excel(name = "实际结束时间", width = 30, dateFormat = "yyyy-MM-dd")
    private Date actualEndTime;
}

2.2 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.project.mapper.ProjectMapper">
    
    <resultMap type="com.project.model.Project" id="ProjectResult">
        <result property="projectId"    column="project_id"    />
        <result property="projectName"    column="project_name"    />
        <result property="deptId"    column="dept_id"    />
        <result property="constrDeptId"    column="constr_dept_id"    />
        <result property="status"    column="status"    />
        <result property="planStartTime"    column="plan_start_time"    />
        <result property="actualStartTime"    column="actual_start_time"    />
        <result property="planEndTime"    column="plan_end_time"    />
        <result property="actualEndTime"    column="actual_end_time"    />
        <result property="delFlag"    column="del_flag"    />
        <result property="createBy"    column="create_by"    />
        <result property="createTime"    column="create_time"    />
        <result property="updateBy"    column="update_by"    />
        <result property="updateTime"    column="update_time"    />
        <result property="deptName"    column="dept_name"    />
        <result property="teamDeptName"    column="team_dept_name"    />
        <collection property="projectStages" javaType="java.util.List" resultMap="ProjectStageResult"/>
    </resultMap>
    <resultMap type="com.project.model.ProjectStage" id="ProjectStageResult">
        <result property="proStageId"    column="pro_stage_id"    />
        <result property="proStageName"    column="pro_stage_name"    />
        <result property="projectId"    column="project_id"    />
        <result property="constrDeptId"    column="constr_dept_id"    />
        <result property="status"    column="status"    />
    </resultMap>

    <sql id="selectProjectVo">
        select project_id, project_name, dept_id, constr_dept_id, status, plan_start_time,
        actual_start_time, plan_end_time, actual_end_time, del_flag, create_by, create_time,
        update_by, update_time,
        d.dept_name, ur.dept_name as team_dept_name
        from _project 
        left join _dept d on dept_id = d.dept_id
        left join _dept ur on constr_dept_id = ur.dept_id
        left join _project_stage r on project_id = r.project_id
    </sql>
</mapper>

在这里插入图片描述
在这里插入图片描述

总结

  1. 一对一/一对多可以将对象封装到对象中,直接通过多表联查查询;
  2. 也可以将需要的属性拿出来,通过< resultMap > 映射出来
  3. 您也可以构造一个VO对象,然后在业务层多次调用数据库,构造出前端需要的数据;
  4. 尽量不要懒惰哦!

注:

我的方式可能不规范,还请大家多多指正;谢谢大家啦!!!

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