Mybatis: How can I get the first element from the passed parameter? - sql

Question

Given that my parameterType is an ArrayList, is it possible to get the first element from that list and use it in the where clause ?
<?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="db">
<select id="selectFlag" resultType="java.lang.Boolean" parameterType="java.util.ArrayList">
select TOP 1 'true' from customers where id = ???
</select>
</mapper>

Answer 1

If your query uses one id, why are you sending a list and then picking the first one for the query?
Change your parameterType to an int (or whatever type the id has), don't send a list. This is a simple approach that also conveys the information that you are only retrieving data based on a single id. Your condition then changes to something like:
where id = #{id}
If you must absolutely send an ArrayList (for whatever reason) then MyBatis supports OGNL expressions so something like this should work:
where id = #{list[0]}
Unfortunately MyBatis lacks on the documentation side, so you can find out about things like this only by looking at the source code.