graphql-gateway-tools

A set of tools to help you build a GraphQL Gateway using remote schemas and schema stitching.

SchemaGenerator

A higher order helper for creating a merged schema. It makes it easy to compose a schema, by providing methods to add remote schema endpoints, local GraphQL schemas, partial type definitions, and multiple resolver functions.

const schemaGenerator = new SchemaGenerator()

// Create a remoteExecutableSchema by specifying the endpoint address
await schemaGenerator.registerEndpoint({uri: 'http://myendpointaddress/graphql'})

// Create a remoteExecutableSchema by specifying endpoint adddress and introspection schema:
await schemaGenerator.registerEndpoint({uri: 'http://myendpointaddress/graphql', introspectionSchema: myIntrospectionSchema})

// Create a remoteExecutableSchema by passing in an ApolloLink instance
await schemaGenerator.registerEndpoint({link: myApolloLink})

// Create a remoteExecutableSchema that uses an Authorization bearer token
await schemaGenerator.registerEndpoint({uri: 'http://myendpointaddress/graphql', authenticationToken: 'ey.......'})

// Add a schema 
schemaGenerator.registerSchema(schema: myGraphQLSchema)

// Add a type definition
schemaGenerator.registerTypeDefinition(typeDefs: myTypeDefinitionString)
    
// Add a resolver function
schemaGenerator.registerResolver(resolverFunction: myResolverFunction)

// Generate the merged schema
const mySchema = schemaGenerator.generateSchema()

See the examples folder for a complete example (coming soon).

addTypeNameField

If you add an Interface Types to your merged schema, you have to manually add the __typeName field to your resolvers. This helper function makes it easy to do so.

// Assuming you have created a remote schema mySchema with types Car and Boat

const typeDefs = `
    interface Verhicle {
        maxSpeed: Float
    }

    extend type Car implements Vehicle { }

    extend type Boat implements Vehicle { }
    
    extend type Query {
        allVehicles: [Verhicle]
    }`

const schema = mergeSchemas({
    schemas: [mySchema],
    resolvers: mergeInfo => ({
        Query: {
            allVehicles: {
                async resolve(parent, args, context, info){
                    const newInfo = addTypeNameField(info)

                    const cars = mergeInfo.delegate('query', 'allCars', args, context, info)
                    const boats = mergeInfo.delgate('query', 'allBoats', args, context, info)

                    return [...cars, ...boats]
                }
            }
        }
    })
})

addFields(mergeInfo: MergeInfo, fields: Array<FieldNode | string>)

A generic helper for adding fields to the resolveInfo, by passing in a fieldName, or a complete FieldNode.

const myField: FieldNode = { kind: 'Field', name: { kind: 'Name', value: 'myField' } }
const anotherField: 'anotherField'

addFields(mergeInfo, [myField, anotherField])