JSONPath Exists Check — Filter by Property Existence

Exists Check in JSONPath

An exists check filters array elements based on whether a specific property is present, regardless of its value. Simply referencing a property inside [?()] without a comparison operator performs an existence test.

Syntax

$.array[?(@.property)]       // elements where property exists
$.array[?(!@.property)]      // elements where property does NOT exist (some implementations)

How It Works

Given:

{
  "items": [
    { "name": "Widget", "price": 9.99, "discount": 0.10 },
    { "name": "Gadget", "price": 24.99 },
    { "name": "Doohickey", "price": 4.99, "discount": 0.05 },
    { "name": "Thingamajig", "price": 14.99 }
  ]
}

• $.items[?(@.discount)] returns Widget and Doohickey — the items that have a discount property.
• $.items[?(@.discount)].name returns ["Widget", "Doohickey"].

What Counts as "Exists"?

The exists check verifies that the property is defined on the object. Important nuances:

Value	Exists?	Notes
"hello"	Yes	Non-empty string
0	Yes	Zero is a valid value
false	Yes*	Boolean false — behavior varies by implementation
null	Yes*	Null means defined but empty — varies by implementation
(missing)	No	Property not in the object

Some implementations treat null and false as "not existing" because they are falsy. Always test with your specific JSONPath library.

Practical Patterns

1. Find incomplete records: $.users[?(!@.email)] — users without email addresses.
2. Find enriched data: $.products[?(@.metadata)] — products that have metadata attached.
3. Conditional processing: check for optional fields before accessing them.

Combining Exists with Other Conditions

$.items[?(@.discount && @.price > 10)]

This selects items that both have a discount property AND a price greater than 10.