Implementation:Apache Druid Parameter Model

Knowledge Sources	Apache_Druid
Domains	Web_Console, Data_Visualization
Last Updated	2026-02-10 10:00 GMT

Overview

The Parameter model defines the type system and utility functions for managing configurable parameters within explore view visualization modules.

Description

This module provides the ParameterDefinition type hierarchy, which supports typed parameters including string, boolean, number, option (single selection), options (multi-selection), expression, expressions, measure, and measures. Each parameter definition can declare labels, default values, visibility conditions, sticky persistence, transfer groups for cross-module parameter migration, and validation rules -- all expressed as static values or functors that receive the current query context. The module also provides utility functions for inflating serialized parameter values, removing undefined parameters, computing effective defaults, and renaming columns within parameter values.

Usage

The Parameter model is used when registering modules in the ModuleRepository (each module declares its parameters as a Record of ParameterDefinition), by the ControlPane for rendering parameter editors, by the ModulePane for filling in defaults and managing sticky state, and by the explore state for serialization and deserialization of module configurations.

Code Reference

Source Location

• Repository: Apache Druid
• File: web-console/src/views/explore-view/models/parameter.ts
• Lines: 1-299

Signature

export type OptionValue = string | number;

export type ModuleFunctor<T> =
  | T
  | ((options: {
      querySource: QuerySource | undefined;
      where: SqlExpression;
      parameterValues: ParameterValues;
    }) => T);

export function evaluateFunctor<T>(
  functor: ModuleFunctor<T> | undefined,
  parameterValues: ParameterValues,
  querySource: QuerySource | undefined,
  where: SqlExpression,
): T | undefined;

export type TypedParameterDefinition<Type extends keyof ParameterTypes>;
export type ParameterDefinition = /* union of all TypedParameterDefinition variants */;
export type ParameterValues = Readonly<Record<string, any>>;
export type Parameters = Readonly<Record<string, ParameterDefinition>>;

export function getModuleOptionLabel(
  optionValue: OptionValue,
  parameterDefinition: ParameterDefinition,
): string;

export function inflateParameterValues(
  parameterValues: ParameterValues | undefined,
  parameters: Parameters,
): ParameterValues;

export function removeUndefinedParameterValues(
  parameterValues: ParameterValues,
  parameters: Parameters,
  querySource: QuerySource | undefined,
  where: SqlExpression,
): ParameterValues;

export function effectiveParameterDefault(
  parameter: ParameterDefinition,
  parameterValues: ParameterValues,
  querySource: QuerySource | undefined,
  where: SqlExpression,
  previousParameterValue: any,
): any;

export function renameColumnsInParameterValues(
  parameterValues: ParameterValues,
  parameters: Parameters,
  rename: Map<string, string>,
): ParameterValues;

Import

import {
  ParameterDefinition,
  ParameterValues,
  inflateParameterValues,
  effectiveParameterDefault,
} from './views/explore-view/models/parameter';

I/O Contract

Inputs

Name	Type	Required	Description
type	keyof ParameterTypes	Yes	The parameter type: 'string', 'boolean', 'number', 'option', 'options', 'expression', 'expressions', 'measure', or 'measures'
label	ModuleFunctor<string>	No	Display label for the parameter, can be a string or functor
defaultValue	ModuleFunctor<T>	No	Default value or functor that computes it from the current query context
sticky	boolean	No	Whether the parameter value should persist across module changes via localStorage
transferGroup	string	No	Group identifier used to transfer values when switching between compatible modules
required	ModuleFunctor<boolean>	No	Whether the parameter is required
important	boolean	No	Whether the parameter should be shown prominently in the compact control pane
visible	ModuleFunctor<boolean>	No	Whether the parameter should be visible in the UI
defined	ModuleFunctor<boolean>	No	Whether the parameter is defined (undefined parameters are removed from state)

Outputs

Name	Type	Description
ParameterValues	Record<string, any>	Inflated, validated, and default-filled parameter values ready for module consumption

Usage Examples

Defining parameters for a module

const parameters: Record<string, ParameterDefinition> = {
  splitColumn: {
    type: 'expression',
    label: 'Group by column',
    transferGroup: 'show',
    required: true,
    important: true,
  },
  measure: {
    type: 'measure',
    defaultValue: ({ querySource }) => querySource?.getFirstAggregateMeasure(),
    required: true,
  },
  limit: {
    type: 'number',
    defaultValue: 10,
    min: 1,
    max: 1000,
  },
};

Inflating serialized parameter values

const inflated = inflateParameterValues(savedValues, module.parameters);

Related Pages

• Environment:Apache_Druid_Web_Console_Development