These two nested aggregations produce the same result, but is one approach better than the other?

Elastic Stack Elasticsearch
1

I have two scenarios that produce identical aggregation results in the final GET order/_search query. The only difference between the two scenarios is where I choose to declare the type: nested in the mapping and what I specify in the nested.path: in the query.

SCENARIO 1 - Declare nested for order_items

PUT order

POST order/_mapping
{
  "properties": {
    "order_items": {
      "type": "nested",
      "properties": {
        "product_id": {
          "type": "long"
        },
        "product": {
          "properties": {
            "name": {
              "type": "keyword"
            },
            "product_id": {
              "type": "long"
            },
            "price": {
              "type": "long"
            }
          }
        }
      }
    }
  }
}

POST order/_bulk
{"index":{}}
{"order_items":[{"product":{"name":"book","price":10}},{"product":{"name":"pencil","price":1}}]}
{"index":{}}
{"order_items":[{"product":{"name":"pen","price":5}},{"product":{"name":"eraser","price":1}}]}


GET order/_search
{
  "size": 0,
  "aggs": {
    "order": {
      "nested": {
        "path": "order_items"
      },
      "aggs": {
        "product_name" : {
          "terms": {
            "field": "order_items.product.name"
          },
          "aggs": {
            "avg_price": {
              "avg": {
                "field": "order_items.product.price"
              }
            }
          }
        }
      }
    }
  }
}

SCENARIO 2 - Declare nested for product

PUT order

POST order/_mapping
{
  "properties": {
    "order_items": {
      "properties": {
        "product_id": {
          "type": "long"
        },
        "product": {
          "type": "nested",
          "properties": {
            "name": {
              "type": "keyword"
            },
            "product_id": {
              "type": "long"
            },
            "price": {
              "type": "long"
            }
          }
        }
      }
    }
  }
}

POST order/_bulk
{"index":{}}
{"order_items":[{"product":{"name":"book","price":10}},{"product":{"name":"pencil","price":1}}]}
{"index":{}}
{"order_items":[{"product":{"name":"pen","price":5}},{"product":{"name":"eraser","price":1}}]}


GET order/_search
{
  "size": 0,
  "aggs": {
    "order": {
      "nested": {
        "path": "order_items.product"
      },
      "aggs": {
        "product_name" : {
          "terms": {
            "field": "order_items.product.name"
          },
          "aggs": {
            "avg_price": {
              "avg": {
                "field": "order_items.product.price"
              }
            }
          }
        }
      }
    }
  }
}

My question is whether one approach is better than the other? Does this have anything to do with field map explosions or other performance concerns? Are there other things I need to be aware of between these two scenarios?

2

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