JSONPath · lesson 10 of 13 · Filters

Existence tests

A bare path inside a filter tests whether it exists — no comparison needed. Put ! in front to test that it doesn't.

Example 1Books that have an ISBN

Document

{
  "store": {
    "book": [
      { "title": "Sayings of the Century", "author": "Nigel Rees",
        "category": "reference", "price": 8.95 },
      { "title": "Sword of Honour", "author": "Evelyn Waugh",
        "category": "fiction", "price": 12.99 },
      { "title": "Moby Dick", "author": "Herman Melville",
        "category": "fiction", "price": 8.99, "isbn": "0-553-21311-3" },
      { "title": "The Lord of the Rings", "author": "J. R. R. Tolkien",
        "category": "fiction", "price": 22.99, "isbn": "0-395-19395-8" }
    ],
    "bicycle": { "color": "red", "price": 19.95 }
  }
}

Query

$.store.book[?@.isbn].title

@.isbn True when the element has an isbn member at all.

Result

"Moby Dick"
"The Lord of the Rings"

Try it in the playground

Example 2Books without one

Document

{
  "store": {
    "book": [
      { "title": "Sayings of the Century", "author": "Nigel Rees",
        "category": "reference", "price": 8.95 },
      { "title": "Sword of Honour", "author": "Evelyn Waugh",
        "category": "fiction", "price": 12.99 },
      { "title": "Moby Dick", "author": "Herman Melville",
        "category": "fiction", "price": 8.99, "isbn": "0-553-21311-3" },
      { "title": "The Lord of the Rings", "author": "J. R. R. Tolkien",
        "category": "fiction", "price": 22.99, "isbn": "0-395-19395-8" }
    ],
    "bicycle": { "color": "red", "price": 19.95 }
  }
}

Query

$.store.book[?[email protected]].title

[email protected] The opposite: the element has no isbn member.

Result

"Sayings of the Century"
"Sword of Honour"

Try it in the playground