Creates an object as an instance of the given schema using its default properties.
npm install @lukalabs/json-schema-default-instance
Creates an object as an instance of the given schema using its default properties.
- Accepts multiple schemas, referenced by id.
- Resolves $ref and allOf.
- Instantiates all properties that have a default.
- If requiredOnly = true, ignores properties that are not listed in the required array (see example below).
- If resolveDefaultRefs = true, also resolves references within defaults.
Install with npm install --save json-schema-default-instance
See test/test.js for an example with $ref and allOf.
Simple example below:
``js
const {Instantiator} = require('json-schema-default-instance');
const mySchemas = [
{
"$schema": "http://json-schema.org/draft-04/schema#",
"id": "theSchemaId",
"type": "object",
"required": [
"firstName",
"lastName"
],
"properties": {
"firstName": {
"type": "string",
"default": "Foo"
},
"lastName": {
"type": "string",
"default": "Bar"
},
"optionalProperty": {
"type": "string",
"default": "Hello"
}
}
}
]
/ Instantiate with all properties /
let ins = new Instantiator(mySchemas);
let myDefaultInstance = ins.instantiate('theSchemaId');
console.log(myDefaultInstance);
// => { firstName: 'Foo', lastName: 'Bar', optionalProperty: 'Hello' }
/ This time, only with required properties /
ins.requiredOnly = true;
let myRequiredInstance = ins.instantiate('theSchemaId');
console.log(myRequiredInstance);
// => { firstName: 'Foo', lastName: 'Bar' }
`
Relies heavily on Ajv for caching and lookup by ref, even though no validation is done here.
Ajv: Another JSON Schema Validator
Ajv does have its own useDefaults option which can be used instead of this package,default
but it does not support keywords in subschemas or allOf.allOf
If you don't need , just use Ajv` directly (see Ajv assigning-defaults and related discussion).
Performance: this code recursively walks through the schema on each call, which can negatively impact performance.
Depending on the use case, it may make sense to precompute the defaults and cache them to an object or module.
Need help understanding JSON Schema? I would recommend the Space Telescope Science Institute's Understanding JSON Schema
Public Domain