get-graphql-from-jsonschema gets a GraphQL schema from a JSON schema.

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$ npm install get-graphql-from-jsonschema

First you need to add a reference to get-graphql-from-jsonschema to your application:

import { getGraphqlFromJsonSchema } from 'get-graphql-from-jsonschema';

To get a GraphQL schema from a JSON schema, call the getGraphqlFromJsonSchema function and hand over the root name of the schema you want to convert as well as the schema itself. As a result, you get back the root GraphQL type name and, if needed, additional GraphQL type definitions:

It is discouraged to use this library without TypeScript. Not the entire json-schema specification can be translated to graphql and that is why we only support a really specific subset of json-schema. This subset is enforced at compile time using typescript types and not at run time using checks. This means using unsupported parts of json-schema can lead to silent misbehaviour in javascript.

const { typeName, typeDefinitions } = getGraphqlFromJsonSchema({
  rootName: 'person',
  schema: {
    type: 'object',
    properties: {
      firstName: { type: 'string' },
      lastName: { type: 'string' },
      coordinates: {
        type: 'object',
        properties: {
          latitude: { type: 'number' },
          longitude: { type: 'number' }
        },
        required: [ 'latitude', 'longitude' ],
        additionalProperties: false
      },
      tags: {
        type: 'array',
        items: {
          type: 'object',
          properties: {
            key: { type: 'string' },
            value: { type: 'string' }
          },
          required: [ 'key', 'value' ],
          additionalProperties: false
        }
      }
    },
    required: [ 'firstName', 'tags' ],
    additionalProperties: false
  }
});

console.log(typeName);
// => PersonT0

console.log(typeDefinitions);
// => [
//      'type PersonT0CoordinatesT0 {
//        latitude: Float!
//        longitude: Float!
//      }',
//      'type PersonT0TagsT0T0 {
//        key: String!
//        value: String!
//      }',
//      'type PersonT0 {
//        firstName: String!
//        lastName: String
//        coordinates: PersonT0CoordinatesT0
//        tags: [PersonT0TagsT0T0]!
//      }'
//    ]

The T0 suffixes are due to enumerating the types in each schema. If a schema has multiple types, they are noted with increasing indexes, to differentiate them in resulting union types. This also happens with oneOf or anyOf constructs.

If you want to use the generated types as input types for a mutation, additionally provide the direction option to the call to getGraphqlFromJsonSchema and set its value to input:

const { typeName, typeDefinitions } = getGraphqlFromJsonSchema({
  rootName: 'person',
  schema: {
    // ...
  },
  direction: 'input'
});

The oneOf and anyOf keywords are supported with a limitation on their usage: There must be no other properties on the same level as either of them.

const { typeName, typeDefinitions } = getGraphqlFromJsonSchema({
  rootName: 'foobar',
  schema: {
    oneOf: [
      {
        type: 'number'
      },
      {
        type: 'object',
        properties: {
          foo: { type: 'string' },
          bar: { type: 'number' }
        },
        required: [ 'foo' ],
        additionalProperties: false
      }
    ]
  }
});

console.log(typeName);
// => Foobar

console.log(typeDefinitions);
// => [
//     'type FoobarI1T0 {
//       foo: String!
//       bar: Float
//     }',
//     'union Foobar = Float | FoobarI1T0'
// ]

Unfortunately, it is not possible to map every aspect of a JSON schema to a GraphQL schema. When using getGraphqlFromJsonSchema, the following limitations apply:

• The null type is not allowed as there is no type comparable to null in GraphQL.
• The keyword allOf is not allowed, because it is not possible to construct a GraphQl type that correctly catches the constraints of allOf in all cases.
• The keywords if, then, else and format are not allowed as well.
• The patternProperties, maxProperties, minProperties, dependencies and propertyNames fields are not allowed. The additionalProperties field must be set to false because GraphQL demands precisely defined types.
• Even though the $ref and definitions properties might be able to be implemented in GraphQl they are currently NOT supported.
• Most of the json-schema fields cannot be mapped to GraphQL in the sense that is still possible to store values that do not match the json schema. You will still need to validate the values using this schema before interacting with GraphQL. It just means that any value that matches this schema will fit the generated GraphQL type.

To run quality assurance for this module use roboter:

$ npx roboter