Mutations

Mutation for Creating Links

Setting up mutations is as easy as queries, following a very similar process.

All GraphQL mutations start from a root type called Mutation.

This type is auto generated in the file app/graphql/types/mutation_type.rb:

Types::MutationType = GraphQL::ObjectType.define do
  name 'Mutation'

  # TODO: Remove me
  field :testField, types.String do
    description "An example field added by the generator"
    resolve ->(obj, args, ctx) {
      "Hello World!"
    }
  end
end

This type is a placeholder for all GraphQL mutations.

To prevent any error when you first start your GraphQL project, it is generated with a dummy testField field.
You will be able to remove it as soon as you add your own mutation below.

The mutation type is automatically exposed in your schema:

GraphqlTutorialSchema = GraphQL::Schema.define do
  query(Types::QueryType)
  mutation(Types::MutationType)
end

Resolvers with Arguments

Now add a resolver for createLink.

For this purpose, you’ll use GraphQL::Function, as mentioned earlier.

Testing with Playground

To test, just restart the server again and use the new mutation with GraphiQL:

Testing with Unit Test

It’s a good practice in Ruby to unit test your resolver objects.

Here is an example of Resolvers::CreateLink test:

require 'test_helper'

class Resolvers::CreateLinkTest < ActiveSupport::TestCase
  def perform(args = {})
    Resolvers::CreateLink.new.call(nil, args, {})
  end

  test 'creating new link' do
    link = perform(
      url: 'http://example.com',
      description: 'description',
    )

    assert link.persisted?
    assert_equal link.description, 'description'
    assert_equal link.url, 'http://example.com'
  end
end