Spread

Transformers have a special spread "key operator": *.

When "*" is used in a transformer as a key inside an object, it will copy all the entries from the resolved object of its value before adding the keys in the spec.

Example

Input

{
  "base": {
    "language": "en"
  }
}

Definition

{
  "*": "$.base",
  "hello": "world"
}

Output

{
  "language": "en",
  "hello": "world"
}

Remove keys

The spread operation can be used to remove keys, here is an example:

Input

{
  "base": {
    "id": "short id",
    "name": "short name",
    "description": "some very long description"
  }
}

Definition

{
  "*": "$.base",
  "description": "#null"
}

Output

{
  "id": "short id",
  "name": "short name"
}

Notice we use #null to select the keys we want to remove, in this case description.

Multiple sources

You can specify more than one source by setting the value to an array:

{
  "*": ["$.base1", "$.base2"],
  "hello": "world"
}

Merge process will be operated in order of array (with the local keys set last as overrides)

This much resembles the ... spread operator in ECMAScript:

result = {
  ...base1,
  ...base2,
  hello: "world"
}