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title: Mapper XML Specification sidebar_position: 10

Contributor contributes new data tables to Apache Linkis. When writing Mapper XML, the following specifications must be followed for development.

1.Basically follow the specifications

• In mapper.xml namespace is equal to java interface address
• The method name in the java interface is the same as the id of the statement in XML
• The input parameter type of the method in the java interface is the same as the type specified by the parameterType of the statement in XML
• The return value type of the method in the java interface is the same as the type specified by the resultType of the statement in XML
• All mysql keywords in XML use lowercase uniformly
• Abstract SQL fragments for excessive query fields
• It is recommended to use Integer for the integer return value type, which can distinguish between unassigned and 0 cases. For example, if the return value is determined to be a number, int can be used. Other data types are similar.
• For placeholders, use #{name} instead of ${name}. Fuzzy query can use CONCAT(‘%’,#{sname},‘%’)
• For sql statement writing, no annotation method is used, and it is uniformly written in the XML file

2.Method name specification

Method Name	Description	Core Points	Recommendations
insert	New data	If it is an auto-incrementing primary key, it should return the primary key ID
deleteById	Delete data according to the primary key ID	sql adds limit 1 by default to prevent multiple deletion of data	This method is not recommended, it is recommended to logically delete
updateById	Modify data according to the primary key ID	sql adds limit 1 by default to prevent multiple data modification
selectById	Query data by primary key	Query a piece of data
selectByIdForUpdate	Query data according to the primary key lock	Query a piece of data by locking, for transaction processing
queryListByParam	Query data list according to input conditions	Multi-parameter query list
queryCountByParam	The total number of queries based on input conditions	The number of multi-parameter queries

3.parameterType specification

The java interface must contain @Param, and the XML can not contain parameterType

3.1 basic type

// java interface
User selectUserById(@Param("id") Integer id);
// XML file
<select id="selectUserById" resultType="userMap">
    select id, name
	from user
	where id = #{id}
</select>

3.2 Collection type

// java interface
List<User> userListByIds(@Param("ids") List<Integer> ids);
// XML file
<select id="userListByIds" resultMap="userMap">
	select id, name
	from user
	where id in
		<foreach collection="ids" separator="," open="(" close=")" item="item">
			#{item}
		</foreach>
</select>

3.3 Map type

// java interface
User queryByParams(@Param("map") Map<String, Object> parasms);
// XML file
<select id="queryByParams" resultMap="userMap">
	select id, name
	from user
	where id = #{map.id} and name = #{map.name}
</select>

3.4 Entity Type

// java interface
User queryByUser(@Param("user") User user);
// XML file
<select id="queryByUser" resultMap="userMap">
	select id, name
	from user
	where id = #{user.id} and name = #{user.name}
</select>

3.5 Multiple parameter types

// java interface
User queryByIdAndName(@Param("id") Integer id, @Param("name") String name);
// XML file
<select id="queryByIdAndName" resultMap="userMap">
	select id, name
	from user
	where id = #{id} and name = #{name}
</select>

4.XML file writing example

Use spaces and indentation reasonably to enhance readability. Examples of various types of SQL statements are as follows

<!DOCTYPE mapper PUBLIC "-//mybatis.org//DTD Mapper 3.0//EN" "http://mybatis.org/dtd/mybatis-3-mapper.dtd">
<mapper namespace="org.apache.linkins.dao.mapper.UserMapper">
	-- add a statement
	<insert id="insert">
		insert into user (id, name)
		values ​​(1, 'z3');
	</insert>

	-- delete statement
	<delete id = "deleteUserByIdAndName">
		delete from user
		where name = #{name}
			and id = #{id}
	</delete>

	-- modify the statement
	<update id="updateUserById">
		update user
		set name = #{name}
		where id = #{id}
	</update>

	-- Check for phrases
	<select id="selectUserByName" resultMap="userMap">
		select id, name
		from user
		where name = 'z3'
	</select>

	-- sql fragment
	<sql id="user">
		id,
		name
	</sql>
	-- Quote
	<include refid="user"/>

	-- resultMap
	<resultMap type="Assets" id="userMap">  
		<id property="id" column="id" />  
		<result property="name" column="name" />
	</resultMap>
	-- Quote
	<select id="queryListByParam" parameterType="map" resultMap="userMap">
		do...
	</select>

	-- conditional judgment
	<if test="name != null and name != ''">  
		name = #{name}  
	</if>

	-- sub query
	<select id="selectUserByTeacherIdAndName" resultMap="userMap">
		select u.id, u.name
		from user u
		where u.name in (
			select t.name
			from teacher t
			where t.id = 1
				and t.name = 'z3'
			)
			and u.id = 2
	</select>
</mapper>