‘is undefined’

The unary postfix operator ‘is not undefined’ is used to check whether a value exists and is defined in JsonQL expressions. It returns a boolean result (true or false).

Note

This operator verifies that a value exists and is accessible. To check specifically that a value is not JSON null, use the ‘is not null’ operator instead.

Operator Priority: 300

Operator Operands

  • Operand 1:

    • Type: any valid JsonQL expression (including invalid path).

    • Description: The value or expression to be checked for defined status.

Evaluation Rules

The is not undefined operator follows these evaluation rules:

  • Invalid paths: Returns false for paths that don’t exist in the JSON structure

  • Empty query results: Returns false when a query returns no results (e.g., First() with no matching items)

  • Valid values: Returns true for any existing value, including:

    • JSON null values

    • Numbers, strings, booleans

    • Objects and arrays

    • Empty collections

Important

The is not undefined operator is the logical inverse of is undefined:

  • Returns true when a value or path exists and is accessible

  • Returns false when a value is missing or a path is invalid

This operator is useful for:

  • Validating that a JSON path exists before using it

  • Checking if a query produced any results

  • Ensuring a value is available for further operations

Note that JSON null values are considered “defined” and will return true.

Examples

{
  "Comment_Operator_is_undefined_1": "(invalid.path is undefined) evaluates to true.",
  "Operator_is_undefined_1": "$value(invalid.path is undefined)",
  "Operator_is_undefined_2": "$value(NullValue is undefined == false)",
  "Operator_is_undefined_3": "$value(Int1 is undefined == true)",
  "Operator_is_undefined_5": "$value(Companies.Select(c => c.Employees).First() is undefined == false)",
  "Operator_is_undefined_6": "$value(Companies.Select(c => c.Employees).First(e => e.Age > 200) is undefined)"
}