Examples of common operations in the mapper.xml mapping file

The mapper.xml file is a mapping file of the mapper interface class, which is used to store database SQL operation statements

1. Insert data:

1) Insert data into a known table:

 <insert id="addCategory" useGeneratedKeys="true" keyProperty="id">
      INSERT INTO category (id,name,label,logo_type)
      VALUES (#{id},#{name},#{label},#{logoType});
 </insert>

2) Insert data into the dynamic table:

 <insert id="insertExhibitImgUrl" useGeneratedKeys="true" keyColumn="id">
        INSERT INTO ${tableName} (imgurl)
        VALUES (#{imgurl});
 </insert>

3) Notes:

2. Delete data:

1) Delete an item of matching data:

<delete id="deleteExhibitImgUrl">
       DELETE FROM ${tableName} WHERE id=#{id};
</delete>

2) Delete the records in the entire table:

<delete id="deleteExhibitContent">
        DELETE FROM ${tableName};
</delete>

3. Update data and tables

1) Update a certain data in the table according to the condition:

 <update id="updateBannerUrlById">
        UPDATE banner
        <set>
           <if test="imgUrl !=null">
               img_url=#{imgUrl}
           </if>
        </set>
        WHERE banner_id=#{bannerId};
</update>

2) create table

<update id="createExhibitImgTable" useGeneratedKeys="true" keyProperty="id">
        CREATE table ${tableName}
        (id int NOT NULL AUTO_INCREMENT,imgurl varchar(255),PRIMARY KEY (id));
</update>

4. Query data

1) Count the number of data items in the table

<select id="count" resultType="int">
       SELECT count(*) FROM banner;
</select>

2. Query qualified data

<select id="getBannerById" resultMap="GetBannersMap">
        SELECT <include refid="BannersQueryFields"></include>
        FROM banner
        WHERE banner_id=#{bannerId}
</select>

<resultMap id="GetBannersMap" type="com.example.demo.pojo.vo.BannerVO">
        <id column="banner_id" property="bannerId"></id>
        <result column="img_url" property="imgUrl"></result>
        <result column="a_href" property="abnHref"></result>
        <result column="is_use" property="isUse"></result>
        <result column="need_href" property="needHref"></result>
        <result column="need_imgurl" property="needImgUrl"></result>
        <result column="add_datetime" property="addDatetime"></result>
</resultMap>

<sql id="BannersQueryFields">
       banner_id,img_url,a_href,is_use,need_href,need_imgurl,add_datetime
</sql>

5. Notes

1) Use ${} and #{} as two variable modifiers: except for database and table names, use #, and use $ modifier for table name variables.

2) The tag id attribute value corresponds to the mapper interface method name

3) <set></set> tags are used to store updated content

4) <if></if> conditional statement, the value passed in by test

5) When creating a table, set the primary key auto-increment: (id int NOT NULL AUTO_INCREMENT, imgurl varchar(255), PRIMARY KEY (id)); not null cannot be less, note that the PRIMARY KEY (id) should be placed in the entire brackets, in An error will be reported outside, and the AUTO_INCREMENT setting will increase automatically