solr DIH: field composed by other fields

Question

Here my sql query:

select id, 'AAA' AS one, 'BBB' AS two from tableX

DIH config:

<entity
    name="item"
    query="select id, 'AAA' AS one, 'BBB' AS two from tableX"
    transformer="TemplateTransformer, RegexTransformer">

        <field column="nt1_id" name="id"/>
        <field column="one" name="oneone_s" regex="\w" replaceWith="C"/>
        <field column="two" name="twotwo_s" regex="\w" replaceWith="D"/>
        <field column="three" name="three_s" template="${item.oneone_s}-${item.twotwo_s}"/>

So, three_s is composed by oneone_s field and twotwo_s.

However, when I query documents:

{
    "id":"244027",
    "oneone_s":"CCC",
    "twotwo_s":"DDD",
    "_version_":1682634241556348928},
  {
    "id":"244029",
    "oneone_s":"CCC",
    "twotwo_s":"DDD",
    "_version_":1682634241558446080},
  {
    "id":"244031",
    "oneone_s":"CCC",
    "twotwo_s":"DDD",
    "_version_":1682634241558446081},
  {
     ...

EDIT:

I've tried setting a fixed value on three_s field:

<field column="three" name="three_s" template="fixed-value"/>

three_s value is created:

{
    "id":"244482",
    "oneone_s":"CCC",
    "twotwo_s":"DDD",
    "three_s":"fixed-value",
    "_version_":1682896666575765504},
{
   ...

Any ideas?