This module creates a mapper function using JMESPath to convert an object to a JSON the schema defines. You can write a JMESPath expression in description to extract the defined data against the input data. Code blocks in Markdown with th prefix "query:" allow you to define the JMESPath expression in description. Thus, the body of the expression must be wrapped with backtick quotes (`).

The JSON schema example:

{
  "type": "object",
  "properties": {
    "ProductID": {
      "description": "query:`prod.id`",
      "type": "string"
    },
    "Price": {
      "description": "The price of the product (query:```prod.price[0]```)",
      "type": "number"
    },
    "NumOfParts": {
      "description": "query:```prod.parts[] | length(@)``` is the number of the parts",
      "type": "integer"
    }
  }
}

To create a mapper function and execute the mapper against the input object:

const mapper = require('json-schema-defined-mapper');

try {
  const product = await mapper(schema);
} catch (e) {
  console.log(e);
}

console.log(product(
{
  prod: {
    id: 'R2D2',
    price: [ 1000000, 2000000, 3000000 ],
    parts: [
      { name: 'head' },
      { name: 'legs' },
      { name: 'body' },
    ]
  }
}
));
/*
{
  "ProductID": "R2D2",
  "Price": 1000000,
  "NumOfParts": 3
}
*/

Note that the mapper does not validate the output. If you want to validate the output, please use ajv or other validators.

If there exists queries at the different layers in a schema, the JMESPath expressions of the children must be relative.

The JSON schema example:

{
  "title": "The house number list for my pets",
  "description": "query:```[*]```",
  "type": "array",
  "items": {
    "description": "query:`pet.house`",
    "type": "number"
  }
}

The mapper from the above schema:

const mapper = require('json-schema-defined-mapper');

const houseList = await mapper(schema);
console.log(houseList(
[
  { pet: { name: 'Adele', house: 5 } },
  { pet: { name: 'Joli', house: 2 } },
]
));
// [ 5, 2 ]

In the above example, the expression [*] at the first layer extracts each element from the input array. The expression pet.house at the second layer is evaluated for each element (object) from the first layer.

A result of oneOf, anyOf, or allOf is extracted as follows:

• oneOf: returns the first non-null value in the condition array.
• anyOf and allOf: returns the composite object if an object type is found in the condition array; otherwise, returns a first non-null value in the array.

• Object:
  • Property names and Pattern Properties
  • Property dependencie and Schema dependencies
• Combining schemas:
  • not

Please see the samples:

• *.schema.json: the JSON schema file.
• *.input.json: an input for the mapper which the schema creates.
• *.expected.json: the expected mapper output against the input.

MIT