pentaho/pentaho-kettle · error · KettleValueException

Please specify a Boolean type for field [

Error message

Please specify a Boolean type for field [

What it means

KettleValueException thrown in Formula.calcFields() when the formula evaluates to a Boolean but the output field's declared value type is not ValueMetaInterface.TYPE_BOOLEAN. The step will not coerce Boolean results to String/Number automatically.

Solutions

  1. Set the output field Type to Boolean in the Formula step dialog.
  2. Or convert the result to a non-boolean explicitly: IF([a]>10; 1; 0) with type Number, or IF([a]>10;"Y";"N") with type String.
  3. Re-run the step's field-type inference after editing formulas.

Example fix

// before
fn.setValueType(ValueMetaInterface.TYPE_STRING); // formula: [x]>0
// after
fn.setValueType(ValueMetaInterface.TYPE_BOOLEAN);
Defensive patterns

Strategy: validation

Validate before calling

if (result instanceof Boolean && fn.getValueType() != ValueMetaInterface.TYPE_BOOLEAN) {
  fn.setValueType(ValueMetaInterface.TYPE_BOOLEAN);
}

Type guard

if (result instanceof Boolean && fn.getValueType() != ValueMetaInterface.TYPE_BOOLEAN) { throw new IllegalArgumentException("Declare Boolean type for " + fn.getFieldName()); }

Prevention

When it happens

Trigger: A formula such as "[a] > 10" or a comparison returning Boolean is assigned to a field whose Type column is String, Number, Integer, etc.

Common situations: Adding a boolean filter column with output type left as default String; changing a formula from numeric to comparison without updating the declared output type.

Understand the failure class

Background: Type mismatch errors: IllegalArgumentException, TypeError and type guards across 150 open-source libraries — this error's family across 150 libraries.

Related errors

AI-assisted analysis of pentaho/pentaho-kettle@f3058517a1 (2026-09-13). Data as JSON: /api/errors/197367314d918ee1. Report an issue: GitHub.

Appendix: source

Thrown at engine/src/main/java/org/pentaho/di/trans/steps/formula/Formula.java:180

              data.returnType[i] = FormulaData.RETURN_TYPE_DATE;
              fn.setNeedDataConversion( fn.getValueType() != ValueMetaInterface.TYPE_DATE );
            } else if ( formulaResult instanceof BigDecimal ) {
              data.returnType[i] = FormulaData.RETURN_TYPE_BIGDECIMAL;
              fn.setNeedDataConversion( fn.getValueType() != ValueMetaInterface.TYPE_BIGNUMBER );
            } else if ( formulaResult instanceof Number ) {
              data.returnType[i] = FormulaData.RETURN_TYPE_NUMBER;
              fn.setNeedDataConversion( fn.getValueType() != ValueMetaInterface.TYPE_NUMBER );
            // this types we will not make attempt to auto-convert
            } else if ( formulaResult instanceof byte[] ) {
              data.returnType[i] = FormulaData.RETURN_TYPE_BYTE_ARRAY;
              if ( fn.getValueType() != ValueMetaInterface.TYPE_BINARY ) {
                throw new KettleValueException( "Please specify a Binary type for field ["
                  + fn.getFieldName() + "] as a result of formula [" + fn.getFormula() + "]" );
              }
            } else if ( formulaResult instanceof Boolean ) {
              data.returnType[i] = FormulaData.RETURN_TYPE_BOOLEAN;
              if ( fn.getValueType() != ValueMetaInterface.TYPE_BOOLEAN ) {
                throw new KettleValueException( "Please specify a Boolean type for field ["
                  + fn.getFieldName() + "] as a result of formula [" + fn.getFormula() + "]" );
              }
            } else {
              data.returnType[i] = FormulaData.RETURN_TYPE_STRING;
              fn.setNeedDataConversion( fn.getValueType() != ValueMetaInterface.TYPE_STRING );
            }
          }

          int realIndex = ( data.replaceIndex[i] < 0 ) ? tempIndex++ : data.replaceIndex[i];
          outputRowData[realIndex] = getReturnValue( formulaResult, data.returnType[i], realIndex, fn );
        }
      }

      return outputRowData;
    } catch ( Throwable e ) {
      throw new KettleValueException( e );
    }
  }

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