JMESPath · lesson 5 of 15 · Projections

Flatten: []

[] flattens one level of nesting — and, like [*], it starts a projection.

Example 1Before flattening

Document

{
  "team": "Platform",
  "office": { "city": "Berlin", "floor": 3 },
  "members": [
    { "name": "Ada", "age": 36, "role": "lead", "active": true,
      "email": "[email protected]", "skills": ["rust", "sql"] },
    { "name": "Linus", "age": 28, "role": "dev", "active": true,
      "email": null, "skills": ["c", "shell"] },
    { "name": "Grace", "age": 45, "role": "dev", "active": false,
      "skills": ["cobol"] },
    { "name": "Alan", "age": 41, "role": "qa", "active": true,
      "email": "[email protected]", "skills": [] }
  ]
}

Query

members[*].skills

skills Each member's own list of skills — so the result is a list of lists.

Result

[["rust","sql"],["c","shell"],["cobol"],[]]

Try it in the playground

Example 2After flattening

Document

{
  "team": "Platform",
  "office": { "city": "Berlin", "floor": 3 },
  "members": [
    { "name": "Ada", "age": 36, "role": "lead", "active": true,
      "email": "[email protected]", "skills": ["rust", "sql"] },
    { "name": "Linus", "age": 28, "role": "dev", "active": true,
      "email": null, "skills": ["c", "shell"] },
    { "name": "Grace", "age": 45, "role": "dev", "active": false,
      "skills": ["cobol"] },
    { "name": "Alan", "age": 41, "role": "qa", "active": true,
      "email": "[email protected]", "skills": [] }
  ]
}

Query

members[*].skills[]

members[*].skills A list of skill lists.
[] Flatten: merge the inner lists into one flat list (one level only).

Result

["rust","sql","c","shell","cobol"]

Try it in the playground