A stored Painless script example for Elasticsearch Ingest node pipeline to extract certain time unit from a timestamp value.

ReusableTimeUnitExtractionPainlessScript.md

# Create a stored script
PUT _scripts/getTimestampUnitValue
{
  "script": {
    "lang": "painless", 
    "source": """
    def value = ctx[params['field']];
    if (value == null) {
      return;
    }
    
    def timestamp = ZonedDateTime.parse(value);
    def localTimestamp = timestamp.withZoneSameInstant(ZoneId.of(params['timezone'])).toLocalDateTime();
    def get = params['get'];
    def target = params['target_field'];
    
    if (get == 'month') {
      ctx[target] = localTimestamp.getMonthValue();
      
    } else if (get == 'dayOfMonth') {
      ctx[target] = localTimestamp.getDayOfMonth();

    } else if (get == 'dayOfYear') {
      ctx[target] = localTimestamp.getDayOfYear();

    }
    """
  }
}

# Reuse the script from ingest pipelines
POST _ingest/pipeline/_simulate
{
  "pipeline": {
    "processors": [
      {
        "script": {
          "id": "getTimestampUnitValue",
          "params": {
            "field": "order_date",
            "get": "month",
            "target_field": "month",
            "timezone": "Asia/Tokyo"
          }
        }
      },
      {
        "script": {
          "id": "getTimestampUnitValue",
          "params": {
            "field": "order_date",
            "get": "dayOfMonth",
            "target_field": "day_of_month",
            "timezone": "Asia/Tokyo"
          }
        }
      },
            {
        "script": {
          "id": "getTimestampUnitValue",
          "params": {
            "field": "order_date",
            "get": "dayOfYear",
            "target_field": "day_of_year",
            "timezone": "Asia/Tokyo"
          }
        }
      }
    ]
  },
  "docs": [
    {
      "_source": {
        "description": "Does not have order_date"
      }
    },
    {
      "_source": {
        "description": "If parsed as UTC, it fill be Feb 28 instead of Mar 1.",
        "order_date": "2022-03-01T00:01:23.456+09:00"
      }
    }
  ]
}

Result:

{
  "docs" : [
    {
      "doc" : {
        "_index" : "_index",
        "_id" : "_id",
        "_source" : {
          "description" : "Does not have order_date"
        },
        "_ingest" : {
          "timestamp" : "2022-03-11T09:33:24.588671723Z"
        }
      }
    },
    {
      "doc" : {
        "_index" : "_index",
        "_id" : "_id",
        "_source" : {
          "order_date" : "2022-03-01T00:01:23.456+09:00",
          "month" : 3,
          "day_of_year" : 60,
          "description" : "If parsed as UTC, it fill be Feb 28 instead of Mar 1.",
          "day_of_month" : 1
        },
        "_ingest" : {
          "timestamp" : "2022-03-11T09:33:24.588678409Z"
        }
      }
    }
  ]
}