How to dynamically select a resultMap and append an incrementing integer value to a “non-existent” column in MyBatis?

Question

I have a certain resultset in MYSQL database using the sakila database on actors and its related tables:

actor_id first_name last_name title
1        PENELOPE   GUINESS   ANACONDA CONFESSIONS
1        PENELOPE   GUINESS   ANGELS LIFE

I have successfully map the following data in MyBatis Plus using the following result map:

    <resultMap id="actor" type="java.util.TreeMap">    
            <result property="id"       column="id" />      
            <result property="firstname"        column="first_name"  />   
            <result property="lastname"         column="last_name"  /> 
           <collection property="movies" javaType="ArrayList" resultMap="movies" />    
    </resultMap>

 <resultMap id="movies" type="java.util.TreeMap">
        <result property="title"    column="title" />      
    </resultMap>

The SQL query looked like this:

<select id="getActors" parameterType="ActorDetailsDTO" resultMap="actor">
select 
    a.actor_id,
    first_name,
    last_name,
    title
from actor a left join
film_actor fa on a.actor_id = fa.actor_id left join
film f on fa.film_id = f.film_id
where a.actor_id = #{id}
</select>

This, in turn achieve the following result:

result :{
    "id" : 1,
    "movies":[
      {
          title : "ANACONDA CONFESSIONS"          
      },
      {
          title : "ANGELS LIFE"          
      },
    ],
    "firstname" : "PENELOPE",
    "lastname"  : "GUINESS"
 }

But I find it difficult to add a "non-existent" column name "movielist" with a value of "blockbuster X" where X is an incrementing number from 1 to N.

I hope to achieve this result:

  result :{
        "id" : 1,
        "movies":[
          {
              "movielist" : "blockbuster 1",
              "title" : "ANACONDA CONFESSIONS"          
          },
          {
              "movielist" : "blockbuster 2",
              "title" : "ANGELS LIFE"          
          },
        ],
        "firstname" : "PENELOPE",
        "lastname"  : "GUINESS"
     }

And, of course, if I have two or more actors, the "blockbuster X" will rest back to 1 to the second actor.

What I've done in the SQL query is I add a variable counter, but the count just continues on counting, not resetting for a new actor.

Thank you for any help you could give.

Answer 1

It should be possible with variables, but here is another approach using a subquery.

<select id="getActors" resultMap="actor">
  select
    a.actor_id,
    first_name,
    last_name,
    fa.film_id,
    concat('blockbuster ', (select count(*) from film_actor fa2
      where a.actor_id = fa2.actor_id and fa2.film_id <= fa.film_id)) movielist,
    title
  from actor a
  left join film_actor fa on a.actor_id = fa.actor_id
  left join film f on fa.film_id = f.film_id
  order by a.actor_id, fa.film_id;
</select>

And here are the result maps.
<id /> elements are added to improve efficiency.

<resultMap id="actor" type="java.util.TreeMap">
  <id property="id" column="actor_id" />
  <result property="firstname" column="first_name" />
  <result property="lastname" column="last_name" />
  <collection property="movies" javaType="list"
    resultMap="movies" />
</resultMap>

<resultMap id="movies" type="java.util.TreeMap">
  <id column="film_id" /><!-- not stored in map -->
  <result property="movielist" column="movielist"
    javaType="string" /><!-- CONCAT returns VARBINARY -->
  <result property="title" column="title" />
</resultMap>