MyBatis how can I generate different sql for different database backend

问题

I'm using mybatis-spring 1.2.3 together with Spring4 to create a web application. The main data storage is MySQL in production environment, but I also use in-memory database H2 in unit testing.

MyBatis works well with both of MySQL and H2 in testing and production, but I come across a problem that one day I need to use force index(idx1) in a query to MySQL, which will cause a syntax error in unit testing as H2 hasn't supported force index. As the result, the unit testing is totally broken.

I want to know is there any way that MyBatis can handle such a situation? (type of database differs in testing and production, and their support of SQL grammar are not identical.)

Here is my mapper file:

<?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="myproject.mapper.UserMapper">
  <select id="getGameUsersForDate" resultType="myproject.dao.domain.GameUser">
    select
    *
    from game_user
    force index(idx1)
    where
    game_id in
    <choose>
      <when test="gameIds.size() > 0">
        <foreach item="gameId" collection="gameIds" open="(" separator="," close=")">
          #{gameId}
        </foreach>
      </when>
      <otherwise>
        (null)
      </otherwise>
    </choose>
    and uid in
    <choose>
      <when test="uids.size() > 0">
        <foreach item="uid" collection="mids" open="(" separator="," close=")">
          #{mid}
        </foreach>
      </when>
      <otherwise>
        (null)
      </otherwise>
    </choose>
    and `date` = #{date}
  </select>
</mapper>

回答1:

MyBatis provides multi-db vendor support that allows you to structure your SQL differently depending on the database vendor that you use. So you could wrap the problematic code in a test such as:

<if test="_databaseId == 'mysql'">
   force index(idx1)
</if>

See the relevant pieces of documentation here and here.

来源：https://stackoverflow.com/questions/33627012/mybatis-how-can-i-generate-different-sql-for-different-database-backend

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java

spring-boot

MyBatis

spring-mybatis