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Troubleshoot type casting issues in Painless

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Follow these guidelines to avoid type conversion errors in your Painless scripts.

When you perform type casting in Painless scripts, attempting implicit conversions or casting incompatible types without proper validation leads to compilation and runtime errors.

{
  "error": {
    "root_cause": [
      {
        "type": "class_cast_exception",
        "reason": "class_cast_exception: Cannot cast from [double] to [int]."
      }
    ],
    "type": "search_phase_execution_exception",
    "reason": "all shards failed",
    "phase": "query",
    "grouped": true,
    "failed_shards": [
      {
        "shard": 0,
        "index": "products",
        "node": "CxMTEjvKSEC0k0aTr4OM3A",
        "reason": {
          "type": "script_exception",
          "reason": "compile error",
          "script_stack": [
            "...    int discountedPrice = price * discount;  // Err ...",
            "                             ^---- HERE"
          ],
          "script": """
          double price = doc['price'].value;
          double discount = 0.85;
          int discountedPrice = price * discount;
          emit(discountedPrice);
        """,
          "lang": "painless",
          "position": {
            "offset": 112,
            "start": 87,
            "end": 137
          },
          "caused_by": {
            "type": "class_cast_exception",
            "reason": "class_cast_exception: Cannot cast from [double] to [int]."
          }
        }
      }
    ],
    "caused_by": {
      "type": "class_cast_exception",
      "reason": "class_cast_exception: Cannot cast from [double] to [int]."
    }
  },
  "status": 400
}
  1. Error: implicit cast 
{
  "runtime_mappings": {
    "discounted_price": {
      "type": "long",
      "script": {
        "source": """
          double price = doc['price'].value;
          double discount = 0.85;
          int discountedPrice = price * discount;
          emit(discountedPrice);
        """
      }
    }
  }
}
  1. Error: implicit cast 
PUT products/_doc/1
{
  "name": "Laptop",
  "price": 999.99
}

PUT products/_doc/2
{
  "name": "Mouse",
  "price": 25
}

Painless has specific rules for implicit and explicit type casting between numeric types. While some numeric conversions are allowed implicitly (widening conversions such as int into double), narrowing conversions such as double to int require explicit casting. The script attempts to assign a double result to an int variable without explicit casting, which causes a compilation error since this is a narrowing conversion that could lose precision. Additionally, field values may be null or of unexpected types, requiring proper validation before casting.

Use explicit casting with proper validation:

POST products/_search
{
  "fields": [
    {
      "field": "*",
      "include_unmapped": "true"
    }
  ],
  "runtime_mappings": {
    "discounted_price": {
      "type": "long",
      "script": {
        "source": """
          if (doc['price'].size() > 0) {
            def value = doc['price'].value;

            if (value != null && value instanceof Number) {
              double price = (double) value;
              double discount = 0.85;
              long discountedPrice = (long)(price * discount);
              emit(discountedPrice);
            } else {
              emit(0L);
            }
          } else {
            emit(0L);
          }
        """
      }
    }
  }
}
		
{
  ...,
  "hits": {
    ...,
    "hits": [
      {
        "_index": "products",
        "_id": "1",
        "_score": 1,
        "_source": {
          "name": "Laptop",
          "price": 999.99
        },
        "fields": {
          "name": [
            "Laptop"
          ],
          "name.keyword": [
            "Laptop"
          ],
          "price": [
            999.99
          ],
          "discounted_price": [
            849
          ]
        }
      },
      {
        "_index": "products",
        "_id": "2",
        "_score": 1,
        "_source": {
          "name": "Mouse",
          "price": 25
        },
        "fields": {
          "name": [
            "Mouse"
          ],
          "name.keyword": [
            "Mouse"
          ],
          "price": [
            25
          ],
          "discounted_price": [
            21
          ]
        }
      }
    ]
  }
}
  • Validate the existence of a field using .size() > 0 before accessing values.
  • Check for null values using value != null before casting.
  • Use instanceof Number to verify the value is numeric before casting.
  • Handle missing fields gracefully with default values.
  • When working with Elasticsearch field values, always validate the actual field type.