JMESPath · lesson 4 of 15 · Projections

Projections: [] and

[*] is JMESPath's central idea: a projection applies everything to its right to each element and gathers the results — dropping any nulls — into a list.

Example 1Project a field from every element

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[*].name

members An array.
[*] Projection: for every element of the array…
.name …read name. The results are collected into a list.

Result

["Ada","Linus","Grace","Alan"]

Try it in the playground

Example 2Project over an object's values

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

office.*

.* On an object, * projects over its values → ["Berlin",3].

Result

["Berlin",3]

Try it in the playground

Good to know

members[*].email returns only two e-mails: null results are dropped from a projection (Linus's is null, Grace's is missing).