Loss of nested fields when using pipeline

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1

Hello. In opensearch version 2.19, we have a problem. Loss of nested fields when using pipeline. When we try to create an index with nested fields, only one element of the nested object gets into index.

In the example below, only the “descr” fields are included in the index. The name and id fields are missing. There is no such problem in version 2.18.

Example simulate query:

POST /_ingest/pipeline/_simulate
{
  "pipeline": {
    "processors": [
      {
        "text_embedding": {
          "model_id": "BeQ3O5UBwVQ2gq6gyMSO",
          "field_map": {
            "ml_text": "ml_embedding"
          }
        }
      }
    ]
  },
  "docs": [
    {
      "_index": "test_index", 
      "_source": {
        "nested_field": [
          { 
            "id": "value1", 
            "name": "value1", 
            "descr": "value1" 
            
          },
          { 
            "id": "value2", 
            "name": "value2",
            "descr": "value2" 
          }
        ],
        "categories": [
          { 
            "id": "value3", 
            "name": "value3", 
            "descr": "value3" 
            
          },
          { 
            "id": "value4", 
            "name": "value4",
            "descr": "value4" 
          }
        ]
      }
    }
  ]
}

Result:

{
  "docs": [
    {
      "doc": {
        "_index": "test_index",
        "_id": "_id",
        "_source": {
          "nested_field": [
            {
              "descr": "value1"
            },
            {
              "descr": "value2"
            }
          ],
          "categories": [
            {
              "descr": "value3"
            },
            {
              "descr": "value4"
            }
          ]
        },
        "_ingest": {
          "timestamp": "2025-03-18T12:15:00.656183009Z"
        }
      }
    }
  ]
}