Solr DIH: documents are not nested

Question

I'm trying to import some data as nested documents.

I've tried to simplify my problem as much as possible.

Here my parent query:

SELECT 1 AS id,
       'xxx' AS col1,
       'yyy' AS col2
UNION
SELECT 2 AS id,
       'xxx' AS col1,
       'yyy' AS col2
UNION
SELECT 3 AS id,
       'xxx' AS col1,
       'yyy' AS col2

You can see data here:

1 | xxx | yyy
2 | xxx | yyy
3 | xxx | yyy

My child query is:

SELECT 1 AS id,
       1 AS rel_id,
       'aaa' AS col1,
       'bbb' AS col2
UNION
SELECT 2 AS id,
       1 AS rel_id,
       'aaa' AS col1,
       'bbb' AS col2
UNION
SELECT 3 AS id,
       2 AS rel_id,
       'aaa' AS col1,
       'bbb' AS col2
UNION
SELECT 4 AS id,
       3 AS rel_id,
       'aaa' AS col1,
       'bbb' AS col2

Data is:

1 | 1 | aaa | bbb
2 | 1 | aaa | bbb
3 | 2 | aaa | bbb
4 | 3 | aaa | bbb

I'm trying to nest using this DIH configuration:

<entity
    name="item"
    query="select 1 as id, 'xxx' as col1, 'yyy' as col2 union select 2 as id, 'xxx' as col1, 'yyy' as col2 union select 3 as id, 'xxx' as col1, 'yyy' as col2">

        <field column="id" name="id"/>

        <field column="col1" name="column1_s" />
        <field column="col2" name="column2_s" />

    <entity
        name="autor"
        child="true"
        query="select 1 as id, 1 as rel_id, 'aaa' as col1, 'bbb' as col2 union select 2 as id, 1 as rel_id, 'aaa' as col1, 'bbb' as col2 union select 3 as id, 2 as rel_id, 'aaa' as col1, 'bbb' as col2 union select 4 as id, 3 as rel_id, 'aaa' as col1, 'bbb' as col2"
        cacheKey="rel_id" cacheLookup="item.id" cacheImpl="SortedMapBackedCache">

            <field column="node_type" template="autor"/>

            <field column="alt_code" name="id" template="${autor.id}-${autor.rel_id}"/>

            <field column="col1" name="column1_s" />
            <field column="col2" name="column2_s" />


        </entity>
</entity>

However, they are not nested:

$ curl "http://localhost:8983/solr/arxius/select?q=*%3A*"
{
  "responseHeader": {
    "status": 0,
    "QTime": 0,
    "params": {
      "q": "*:*"
    }
  },
  "response": {
    "numFound": 7,
    "start": 0,
    "numFoundExact": true,
    "docs": [
      {
        "id": "1",
        "column2_s": "bbb",
        "column1_s": "aaa",
        "_version_": 1682901366056419300
      },
      {
        "id": "2",
        "column2_s": "bbb",
        "column1_s": "aaa",
        "_version_": 1682901366056419300
      },
      {
        "id": "1",
        "column2_s": "yyy",
        "column1_s": "xxx",
        "_version_": 1682901366056419300
      },
      {
        "id": "3",
        "column2_s": "bbb",
        "column1_s": "aaa",
        "_version_": 1682901366058516500
      },
      {
        "id": "2",
        "column2_s": "yyy",
        "column1_s": "xxx",
        "_version_": 1682901366058516500
      },
      {
        "id": "4",
        "column2_s": "bbb",
        "column1_s": "aaa",
        "_version_": 1682901366058516500
      },
      {
        "id": "3",
        "column2_s": "yyy",
        "column1_s": "xxx",
        "_version_": 1682901366058516500
      }
    ]
  }
}

As you can see, documents are not nested.

I've been struggling a lot over that issue.

I've tried to strightforward the problem.

I hope I've explained so well.

Please, any ideas?