A little NodeJS package to convert OpenAPI Schema Object to JSON Schema.

Currently converts from OpenAPI 3.0 to JSON Schema Draft 4.

OpenAPI is a specification for describing RESTful APIs. OpenAPI 3.0 allows us to describe the structures of request and response payloads in a detailed manner. This would, theoretically, mean that we should be able to automatically validate request and response payloads. However, as of writing there aren't many validators around.

The good news is that there are many validators for JSON Schema for different languages. The bad news is that OpenAPI 3.0 is not entirely compatible with JSON Schema. The Schema Object of OpenAPI 3.0 is an extended subset of JSON Schema Specification Wright Draft 00 with some differences.

The purpose of this project is to fill the grap by doing the conversion between these two formats.

• converts OpenAPI 3.0 Schema Object to JSON Schema Draft 4
• converts common named data types to type and format
  • for example type: "dateTime" becomes type: "string" with format: "date-time"
• deletes nullable and adds "null" to type array if nullable is true
• supports deep structures with nested allOfs etc.
• removes OpenAPI specific properties such as discriminator, deprecated etc. unless specified otherwise
• optionally supports patternProperties with x-patternProperties in the Schema Object

NOTE: $refs are not dereferenced. Use a dereferencer such as json-schema-ref-parser prior to using this package.

npm install --save openapi-schema-to-json-schema

Here's a small example to get the idea:

var toJsonSchema = require('openapi-schema-to-json-schema');

var schema = {
  type: 'dateTime',
  nullable: true
};

var convertedSchema = toJsonSchema(schema);

console.log(convertedSchema);

The example prints out

{
  type: ['string', 'null'],
  format: 'date-time',
  '$schema': 'http://json-schema.org/draft-04/schema#'
}

Provide the function the schema object with possible options.

The function accepts options object as the second argument.

If set to false, converts the provided schema in place. If true, clones the schema by converting it to JSON and back. The overhead of the cloning is usually negligible. Defaults to true.

This is false by default and leaves date type/format as is. If set to true, sets type: "string" and format: "date-time" if

• type: "string" AND format: "date" OR
• type: "date"

For example

var schema = {
  type: 'date'
};

var convertedSchema = toJsonSchema(schema, {dateToDateTime: true});

console.log(convertedSchema);

prints

{
  type: 'string',
  format: 'date-time',
  '$schema': 'http://json-schema.org/draft-04/schema#'
}

By default, the following fields are removed from the result schema: nullable, discriminator, readOnly, writeOnly, xml, externalDocs, example and deprecated as they are not supported by JSON Schema Draft 4. Provide an array of the ones you want to keep (as strings) and they won't be removed.

If set to true and x-patternProperties property is present, change x-patternProperties to patternProperties and call patternPropertiesHandler. If patternPropertiesHandler is not defined, call the default handler. See patternPropertiesHandler for more information.

Provide a function to handle pattern properties and set supportPatternProperties to take effect. The function takes the schema where x-patternProperties is defined on the root level. At this point x-patternProperties is changed to patternProperties. It must return the modified schema.

If the handler is not provided, the default handler is used. If additionalProperties is set and is an object, the default handler sets it to false if the additionaProperties object has deep equality with a pattern object inside patternProperties. This is because we might want to define additionalProperties in OpenAPI spec file, but want to validate against a pattern. The pattern would turn out to be useless if additionalProperties of the same structure were allowed. Create you own handler to override this functionality.

See test/pattern_properties.js for examples how this works.