Mybatis，怀疑--使用--感悟

Posted 2023-01-09 好好生活_

    正当我疯狂地学习Hibernate的时候，接到新项目的电话面试，说底层用的是Mybatis.因为只是听说过，在学习Hibernate的时候，也接触过一些理论方面的东西，因为都属于ORM框架，对两者进行过简单的比较，但都是偏向于Hibernate的角度。所以说，自己对Mybatis可以说是几乎什么都不知道。

    现在还记得那天接到面试电话时的场景，听到Mybatis，很熟悉，但其实是很陌生。关于mybatis，问 的一个问题就是：mybatis的使用方式？因为没有使用过，当然回答的是不知道了。接完面试的电话之 后，自己就开始上网寻找答案。     Mybatis的使用方式包括两种：基于传统方式statementid；基于mapper接口方式调用。答案很具体，但对自己来说，很抽象，因为没有任何接触。     那天，闲着没事，自己又查了查关于Hibernate与Mybatis的比较问题。总结如下：     1. Hibernate的真正掌握要比Mybatis来得难些。Mybatis框架相对简单很容易上手，但也相对简陋些。     2. Hibernate 与Mybatis都是流行的持久层开发框架，但Hibernate开发社区相对多热闹些，支持的工具也多，更新也快，当前最高版本4.1.8。 而Mybatis相对平静，工具较少，当前最高版本3.2。     3. Hibernate和MyBatis都有相应的代码生成工具。可以生成简单基本的DAO层方法。     4. 针对高级查询，Mybatis需要手动编写SQL语句，以及ResultMap。而Hibernate有良好的映射机 制，开发者无需关心SQL的生成与结果映射，可以更专注于业务流程。     至今，自己仍然记得当时对Mybatis有着很大的一个疑问：居然要将SQL写在配置文件里，这是多么麻 烦的一件事情，要是让我开发，我看都不想看了吧。     而如今，接触底层用mybatis的这个项目近两个月了，我对mybatis有了实践之后，不得不说一句自己很片面呀。下面就简单看看mybatis的使用：     有一个好的开发工具，真的可以节省很多工作量。使用mybatis的代码生成工具， mybatis generator, Dao层的代码都不用我们写了，并且很大程度上都能满足我们的开发需要。     每个表生成对应的文件包括：~Mapper.java文件/~.java文件/~Example.java文件以及~Mapper.xml文件。下面是某数据库表生成的对应的四个文件代码如下：

//广告地区实体，与数据库表对应
package com.gac.adv.entity;

import com.gac.core.entity.BaseEntity;
import javax.validation.constraints.*;

public class AdvertRegion extends BaseEntity 
    /**
     * 广告id
     */
    private Long advId;

    /**
     * 地区id
     */
    private Long regionId;

    /**
     * 是否删除0-否；1-是
     */
    private Boolean isDeleted;

    /**
     * nullable:false,length:19
     */
    @NotNull
    public Long getAdvId() 
        return advId;
    

    public void setAdvId(Long advId) 
        this.advId = advId;
    

    /**
     * nullable:false,length:19
     */
    @NotNull
    public Long getRegionId() 
        return regionId;
    

    public void setRegionId(Long regionId) 
        this.regionId = regionId;
    

    /**
     * nullable:false,length:0
     */
    @NotNull
    public Boolean getIsDeleted() 
        return isDeleted;
    

    public void setIsDeleted(Boolean isDeleted) 
        this.isDeleted = isDeleted;
    

//广告地区实体对应的Example
package com.gac.adv.entity.example;

import com.gac.core.entity.example.AbstractExample;
import com.gac.core.entity.example.GeneratedCriteria;
import java.util.List;

public class AdvertRegionExample extends AbstractExample 

    @Override
    public Criteria or() 
        return (Criteria)super.or();
    

    @Override
    public Criteria createCriteria() 
        return (Criteria)super.createCriteria();
    

    @Override
    protected Criteria createCriteriaInternal() 
        return new Criteria();
    

    public class Criteria extends GeneratedCriteria 

        protected Criteria() 
            super();
        

        public Criteria andAdvIdIsNull() 
            addCriterion("adv_id is null");
            return (Criteria) this;
        

        public Criteria andAdvIdIsNotNull() 
            addCriterion("adv_id is not null");
            return (Criteria) this;
        

        public Criteria andAdvIdEqualTo(Long value) 
            addCriterion("adv_id =", value, "advId");
            return (Criteria) this;
        

        public Criteria andAdvIdNotEqualTo(Long value) 
            addCriterion("adv_id <>", value, "advId");
            return (Criteria) this;
        

        public Criteria andAdvIdGreaterThan(Long value) 
            addCriterion("adv_id >", value, "advId");
            return (Criteria) this;
        

        public Criteria andAdvIdGreaterThanOrEqualTo(Long value) 
            addCriterion("adv_id >=", value, "advId");
            return (Criteria) this;
        

        public Criteria andAdvIdLessThan(Long value) 
            addCriterion("adv_id <", value, "advId");
            return (Criteria) this;
        

        public Criteria andAdvIdLessThanOrEqualTo(Long value) 
            addCriterion("adv_id <=", value, "advId");
            return (Criteria) this;
        

        public Criteria andAdvIdIn(List<Long> values) 
            addCriterion("adv_id in", values, "advId");
            return (Criteria) this;
        

        public Criteria andAdvIdNotIn(List<Long> values) 
            addCriterion("adv_id not in", values, "advId");
            return (Criteria) this;
        

        public Criteria andAdvIdBetween(Long value1, Long value2) 
            addCriterion("adv_id between", value1, value2, "advId");
            return (Criteria) this;
        

        public Criteria andAdvIdNotBetween(Long value1, Long value2) 
            addCriterion("adv_id not between", value1, value2, "advId");
            return (Criteria) this;
        

        public Criteria andRegionIdIsNull() 
            addCriterion("region_id is null");
            return (Criteria) this;
        

        public Criteria andRegionIdIsNotNull() 
            addCriterion("region_id is not null");
            return (Criteria) this;
        

        public Criteria andRegionIdEqualTo(Long value) 
            addCriterion("region_id =", value, "regionId");
            return (Criteria) this;
        

        public Criteria andRegionIdNotEqualTo(Long value) 
            addCriterion("region_id <>", value, "regionId");
            return (Criteria) this;
        

        public Criteria andRegionIdGreaterThan(Long value) 
            addCriterion("region_id >", value, "regionId");
            return (Criteria) this;
        

        public Criteria andRegionIdGreaterThanOrEqualTo(Long value) 
            addCriterion("region_id >=", value, "regionId");
            return (Criteria) this;
        

        public Criteria andRegionIdLessThan(Long value) 
            addCriterion("region_id <", value, "regionId");
            return (Criteria) this;
        

        public Criteria andRegionIdLessThanOrEqualTo(Long value) 
            addCriterion("region_id <=", value, "regionId");
            return (Criteria) this;
        

        public Criteria andRegionIdIn(List<Long> values) 
            addCriterion("region_id in", values, "regionId");
            return (Criteria) this;
        

        public Criteria andRegionIdNotIn(List<Long> values) 
            addCriterion("region_id not in", values, "regionId");
            return (Criteria) this;
        

        public Criteria andRegionIdBetween(Long value1, Long value2) 
            addCriterion("region_id between", value1, value2, "regionId");
            return (Criteria) this;
        

        public Criteria andRegionIdNotBetween(Long value1, Long value2) 
            addCriterion("region_id not between", value1, value2, "regionId");
            return (Criteria) this;
        

        public Criteria andIsDeletedIsNull() 
            addCriterion("is_deleted is null");
            return (Criteria) this;
        

        public Criteria andIsDeletedIsNotNull() 
            addCriterion("is_deleted is not null");
            return (Criteria) this;
        

        public Criteria andIsDeletedEqualTo(Boolean value) 
            addCriterion("is_deleted =", value, "isDeleted");
            return (Criteria) this;
        

        public Criteria andIsDeletedNotEqualTo(Boolean value) 
            addCriterion("is_deleted <>", value, "isDeleted");
            return (Criteria) this;
        

        public Criteria andIsDeletedGreaterThan(Boolean value) 
            addCriterion("is_deleted >", value, "isDeleted");
            return (Criteria) this;
        

        public Criteria andIsDeletedGreaterThanOrEqualTo(Boolean value) 
            addCriterion("is_deleted >=", value, "isDeleted");
            return (Criteria) this;
        

        public Criteria andIsDeletedLessThan(Boolean value) 
            addCriterion("is_deleted <", value, "isDeleted");
            return (Criteria) this;
        

        public Criteria andIsDeletedLessThanOrEqualTo(Boolean value) 
            addCriterion("is_deleted <=", value, "isDeleted");
            return (Criteria) this;
        

        public Criteria andIsDeletedIn(List<Boolean> values) 
            addCriterion("is_deleted in", values, "isDeleted");
            return (Criteria) this;
        

        public Criteria andIsDeletedNotIn(List<Boolean> values) 
            addCriterion("is_deleted not in", values, "isDeleted");
            return (Criteria) this;
        

        public Criteria andIsDeletedBetween(Boolean value1, Boolean value2) 
            addCriterion("is_deleted between", value1, value2, "isDeleted");
            return (Criteria) this;
        

        public Criteria andIsDeletedNotBetween(Boolean value1, Boolean value2) 
            addCriterion("is_deleted not between", value1, value2, "isDeleted");
            return (Criteria) this;
        
    

//广告地区Mapper
package com.gac.adv.dao;

import java.util.List;

import com.gac.adv.entity.AdvertRegion;
import com.gac.adv.entity.example.AdvertRegionExample;
import com.gac.core.dao.BaseMapper;

public interface AdvertRegionMapper extends BaseMapper<AdvertRegion, AdvertRegionExample> 
	//自定义的批量插入方法
	void insertBatch(List<AdvertRegion> advertRegion);

<!-- 广告地区表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.gac.adv.dao.AdvertRegionMapper" >
  <resultMap id="BaseResultMap" type="com.gac.adv.entity.AdvertRegion" >
    <id column="id" property="id" jdbcType="BIGINT" />
    <result column="adv_id" property="advId" jdbcType="BIGINT" />
    <result column="region_id" property="regionId" jdbcType="BIGINT" />
    <result column="is_deleted" property="isDeleted" jdbcType="BIT" />
    <result column="create_by" property="createBy" jdbcType="BIGINT" />
    <result column="create_time" property="createTime" jdbcType="TIMESTAMP" />
    <result column="update_by" property="updateBy" jdbcType="BIGINT" />
    <result column="update_time" property="updateTime" jdbcType="TIMESTAMP" />
  </resultMap>
  <sql id="Example_Where_Clause" >
    <where >
      <foreach collection="oredCriteria" item="criteria" separator="or" >
        <if test="criteria.valid" >
          <trim prefix="(" suffix=")" prefixOverrides="and" >
            <foreach collection="criteria.criteria" item="criterion" >
              <choose >
                <when test="criterion.noValue" >
                  and $criterion.condition
                </when>
                <when test="criterion.singleValue" >
                  and $criterion.condition #criterion.value
                </when>
                <when test="criterion.betweenValue" >
                  and $criterion.condition #criterion.value and #criterion.secondValue
                </when>
                <when test="criterion.listValue" >
                  and $criterion.condition
                  <foreach collection="criterion.value" item="listItem" open="(" close=")" separator="," >
                    #listItem
                  </foreach>
                </when>
              </choose>
            </foreach>
          </trim>
        </if>
      </foreach>
    </where>
  </sql>
  <sql id="Update_By_Example_Where_Clause" >
    <where >
      <foreach collection="example.oredCriteria" item="criteria" separator="or" >
        <if test="criteria.valid" >
          <trim prefix="(" suffix=")" prefixOverrides="and" >
            <foreach collection="criteria.criteria" item="criterion" >
              <choose >
                <when test="criterion.noValue" >
                  and $criterion.condition
                </when>
                <when test="criterion.singleValue" >
                  and $criterion.condition #criterion.value
                </when>
                <when test="criterion.betweenValue" >
                  and $criterion.condition #criterion.value and #criterion.secondValue
                </when>
                <when test="criterion.listValue" >
                  and $criterion.condition
                  <foreach collection="criterion.value" item="listItem" open="(" close=")" separator="," >
                    #listItem
                  </foreach>
                </when>
              </choose>
            </foreach>
          </trim>
        </if>
      </foreach>
    </where>
  </sql>
  <sql id="Base_Column_List" >
    id, adv_id, region_id, is_deleted, create_by, create_time, update_by, update_time
  </sql>
  <select id="selectByExample" resultMap="BaseResultMap" parameterType="com.gac.adv.entity.example.AdvertRegionExample" >
    select
    <if test="distinct" >
      distinct
    </if>
    <include refid="Base_Column_List" />
    from cms_adv_region
    <if test="_parameter != null" >
      <include refid="Example_Where_Clause" />
    </if>
    <if test="orderByClause != null" >
      order by $orderByClause
    </if>
    <if test="pageStart!=null and pageStart gt -1" >
       limit $pageStart,$pageSize
    </if>
  </select>
  <select id="selectByPrimaryKey" resultMap="BaseResultMap" parameterType="java.lang.Long" >
    select 
    <include refid="Base_Column_List" />
    from cms_adv_region
    where id = #id,jdbcType=BIGINT
  </select>
  <delete id="deleteByPrimaryKey" parameterType="java.lang.Long" >
    delete from cms_adv_region
    where id = #id,jdbcType=BIGINT
  </delete>
  <delete id="deleteByExample" parameterType="com.gac.adv.entity.example.AdvertRegionExample" >
    delete from cms_adv_region
    <if test="_parameter != null" >
      <include refid="Example_Where_Clause" />
    </if>
  </delete>
  <insert id="insert" parameterType="com.gac.adv.entity.AdvertRegion">
    insert into cms_adv_region (id, adv_id, region_id, 
      is_deleted, create_by, create_time, 
      update_by, update_time)
    values (#id,jdbcType=BIGINT, #advId,jdbcType=BIGINT, #regionId,jdbcType=BIGINT, 
      #isDeleted,jdbcType=BIT, #createBy,jdbcType=BIGINT, #createTime,jdbcType=TIMESTAMP, 
      #updateBy,jdbcType=BIGINT, #updateTime,jdbcType=TIMESTAMP)
  </insert>
  <insert id="insertSelective" parameterType="com.gac.adv.entity.AdvertRegion" >
    insert into cms_adv_region
    <trim prefix="(" suffix=")" suffixOverrides="," >
      <if test="id != null" >
        id,
      </if>
      <if test="advId != null" >
        adv_id,
      </if>
      <if test="regionId != null" >
        region_id,
      </if>
      <if test="isDeleted != null" >
        is_deleted,
      </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>
    </trim>
    <trim prefix="values (" suffix=")" suffixOverrides="," >
      <if test="id != null" >
        #id,jdbcType=BIGINT,
      </if>
      <if test="advId != null" >
        #advId,jdbcType=BIGINT,
      </if>
      <if test="regionId != null" >
        #regionId,jdbcType=BIGINT,
      </if>
      <if test="isDeleted != null" >
        #isDeleted,jdbcType=BIT,
      </if>
      <if test="createBy != null" >
        #createBy,jdbcType=BIGINT,
      </if>
      <if test="createTime != null" >
        #createTime,jdbcType=TIMESTAMP,
      </if>
      <if test="updateBy != null" >
        #updateBy,jdbcType=BIGINT,
      </if>
      <if test="updateTime != null" >
        #updateTime,jdbcType=TIMESTAMP,
      </if>
    </trim>
  </insert>
  
 <insert id="insertBatch" parameterType="java.util.ArrayList" >
    insert into cms_adv_region (adv_id, region_id, is_deleted, create_by, create_time, update_by, update_time)
      values       
     <foreach collection="list" index = "index" item = "item" separator="," >     
      <trim prefix="(" suffix=")" suffixOverrides="," >
	  <choose>
      <when test="item.advId != null" >
        #item.advId,jdbcType=BIGINT,
      </when>
	  <otherwise>
		  '',
		</otherwise>
	  </choose>
	  <choose>
      <when test="item.regionId != null" >
        #item.regionId,jdbcType=BIGINT,
      </when>
	   <otherwise>
		  0,
		</otherwise>
	  </choose>
	  <choose>
      <when test="item.isDeleted != null" >
        #item.isDeleted,jdbcType=BIT,
      </when>
	   <otherwise>
		  0,
		</otherwise>
	  </choose>
	  <choose>
      <when test="item.createBy != null" >
        #item.createBy,jdbcType=BIGINT,
      </when>
	  <otherwise>
		  0,
		</otherwise>
	  </choose>
	  <choose>
      <when test="item.createTime != null" >
        #item.createTime,jdbcType=TIMESTAMP,
      </when>
	   <otherwise>
		 now(),
		</otherwise>
	  </choose>
	  <choose>
      <when test="item.updateBy != null" >
        #item.updateBy,jdbcType=BIGINT,
      </when>
	   <otherwise>
		  0,
		</otherwise>
	  </choose>
	  <choose>
      <when test="item.updateTime != null" >
        #item.updateTime,jdbcType=TIMESTAMP,
      </when>
	   <otherwise>
		 now(),
		</otherwise>
	  </choose>
	  </trim>    
     </foreach>        
  </insert>
  
  <select id="countByExample" parameterType="com.gac.adv.entity.example.AdvertRegionExample" resultType="java.lang.Integer" >
    select count(*) from cms_adv_region
    <if test="_parameter != null" >
      <include refid="Example_Where_Clause" />
    </if>
  </select>
  <update id="updateByExampleSelective" parameterType="map" >
    update cms_adv_region
    <set >
      <if test="record.id != null" >
        id = #record.id,jdbcType=BIGINT,
      </if>
      <if test="record.advId != null" >
        adv_id = #record.advId,jdbcType=BIGINT,
      </if>
      <if test="record.regionId != null" >
        region_id = #record.regionId,jdbcType=BIGINT,
      </if>
      <if test="record.isDeleted != null" >
        is_deleted = #record.isDeleted,jdbcType=BIT,
      </if>
      <if test="record.createBy != null" >
        create_by = #record.createBy,jdbcType=BIGINT,
      </if>
      <if test="record.createTime != null" >
        create_time = #record.createTime,jdbcType=TIMESTAMP,
      </if>
      <if test="record.updateBy != null" >
        update_by = #record.updateBy,jdbcType=BIGINT,
      </if>
      <if test="record.updateTime != null" >
        update_time = #record.updateTime,jdbcType=TIMESTAMP,
      </if>
    </set>
    <if test="_parameter != null" >
      <include refid="Update_By_Example_Where_Clause" />
    </if>
  </update>
  <update id="updateByExample" parameterType="map" >
    update cms_adv_region
    set id = #record.id,jdbcType=BIGINT,
      adv_id = #record.advId,jdbcType=BIGINT,
      region_id = #record.regionId,jdbcType=BIGINT,
      is_deleted = #record.isDeleted,jdbcType=BIT,
      create_by = #record.createBy,jdbcType=BIGINT,
      create_time = #record.createTime,jdbcType=TIMESTAMP,
      update_by = #record.updateBy,jdbcType=BIGINT,
      update_time = #record.updateTime,jdbcType=TIMESTAMP
    <if test="_parameter != null" >
      <include refid="Update_By_Example_Where_Clause" />
    </if>
  </update>
  <update id="updateByPrimaryKeySelective" parameterType="com.gac.adv.entity.AdvertRegion" >
    update cms_adv_region
    <set >
      <if test="advId != null" >
        adv_id = #advId,jdbcType=BIGINT,
      </if>
      <if test="regionId != null" >
        region_id = #regionId,jdbcType=BIGINT,
      </if>
      <if test="isDeleted != null" >
        is_deleted = #isDeleted,jdbcType=BIT,
      </if>
      <if test="createBy != null" >
        create_by = #createBy,jdbcType=BIGINT,
      </if>
      <if test="createTime != null" >
        create_time = #createTime,jdbcType=TIMESTAMP,
      </if>
      <if test="updateBy != null" >
        update_by = #updateBy,jdbcType=BIGINT,
      </if>
      <if test="updateTime != null" >
        update_time = #updateTime,jdbcType=TIMESTAMP,
      </if>
    </set>
    where id = #id,jdbcType=BIGINT
  </update>
  <update id="updateByPrimaryKey" parameterType="com.gac.adv.entity.AdvertRegion" >
    update cms_adv_region
    set adv_id = #advId,jdbcType=BIGINT,
      region_id = #regionId,jdbcType=BIGINT,
      is_deleted = #isDeleted,jdbcType=BIT,
      create_by = #createBy,jdbcType=BIGINT,
      create_time = #createTime,jdbcType=TIMESTAMP,
      update_by = #updateBy,jdbcType=BIGINT,
      update_time = #updateTime,jdbcType=TIMESTAMP
    where id = #id,jdbcType=BIGINT
  </update>
</mapper>

    有了这些代码，我们就可以直接在业务逻辑层直接写增删改查数据表的代码，如新增一条记录：

	/**
	 * 增加广告投放城市
	 * @param userId
	 * @param advId
	 * @param regionIds
	 */
	@Transactional(rollbackFor = Exception.class)
	public void addAdvertRegion(Long userId,Long advId,List<Long> regionIds)
		List<AdvertRegion> advertRegions=new ArrayList<AdvertRegion>();
		for (Long regionId : regionIds) 
			AdvertRegion advertRegion=new AdvertRegion();
			advertRegion.setCreateBy(userId);
			advertRegion.setCreateTime(new Date());
			advertRegion.setRegionId(regionId);
			advertRegion.setAdvId(advId);
			advertRegion.setUpdateBy(userId);
			advertRegion.setUpdateTime(new Date());
			advertRegions.add(advertRegion);
		
		advertRegionMapper.insertBatch(advertRegions);		
	

    上面生成的代码，可以满足基本的增删改查，如果是比较复杂的一些操作，如批量更新/插入/复杂的sql等，我们可以自己在Xml中定义一个新的方法即可，也是非常方便的。     在项目的使用过程中，也遇到过一些问题，比如想要获取新插入记录的id，想要按某个字段去排序，想要返回分页的数据，这些都可以从mybatis着手去解决，而且非常简单，并不需要繁琐的代码，繁琐的程序。     现在想想，当你不知道某个东西的时候，真的不能妄下定论，因为，你还不知道等到你了解了接触了它之后，会产生怎样的火花。但我们可以怀疑，可以猜想，这样最后你得到的答案也一定会带给自己更深 刻的感受，就好像当初我对Mybatis的怀疑一样。