Moving legacy fields to a GraphQL::Enterprise::Changeset

legacy_changesets.rb

require "bundler/inline"

gemfile do
  gem "graphql", path: "./"
  gem "graphql-enterprise", source: "https://gems.graphql.pro"
end

class BaseField < GraphQL::Schema::Field
  include GraphQL::Enterprise::Changeset::FieldIntegration
end

class Thing < GraphQL::Schema::Object
  field_class BaseField
end

class Query < GraphQL::Schema::Object
  field :thing, Thing

  def thing
    { legacy_message: "Ye Olde Message", new_message: "Yo!" }
  end
end

# Make a changeset which includes legacy fields, and choose a long-past date for this version
class LegacyFields < GraphQL::Enterprise::Changeset
  release "1900-01-01"
  modifies Thing do
    field :legacy_message, String
  end
end

class ModernFields < GraphQL::Enterprise::Changeset
  release "2022-12-01"
  modifies Thing do
    field :new_message, String
    remove_field :legacy_message
  end
end

class Schema < GraphQL::Schema
  query(Query)
  use GraphQL::Enterprise::Changeset::Release, changesets: [LegacyFields, ModernFields]
end

# Here's the catch: `changeset_version: nil` won't work as a default, because it will 
# go back to _before_ the legacy changeset above. So instead, update your application to 
# use a default `changeset_version` which is between the long-past legacy changeset 
# and the first "real," new-feature changeset. 
pp Schema.execute("{ thing { legacyMessage } }", context: { changeset_version: "2000-01-01" }).to_h
# {"data"=>{"thing"=>{"legacyMessage"=>"Ye Olde Message"}}}
puts Schema.to_definition(context: { changeset_version: "2000-01-01" })
# type Query {
#   thing: Thing
# }
#
# type Thing {
#   legacyMessage: String
# }

# Then, future changeset won't see legacy fields:
pp Schema.execute("{ thing { newMessage } }", context: { changeset_version: "2023-12-01" }).to_h
# {"data"=>{"thing"=>{"newMessage"=>"Yo!"}}}
puts Schema.to_definition(context: { changeset_version: "2023-01-01" })
# type Query {
#   thing: Thing
# }

# type Thing {
#   newMesssage: String
# }

# { changeset_version: nil } won't work, since the legacy fields won't be on the type:
pp Schema.execute("{ thing { legacyMessage } }", context: { changeset_version: nil }).to_h
# {"errors"=>
#   [{"message"=>"Field 'legacyMessage' doesn't exist on type 'Thing'",
#     "locations"=>[{"line"=>1, "column"=>11}],
#     "path"=>["query", "thing", "legacyMessage"],
#     "extensions"=>{"code"=>"undefinedField", "typeName"=>"Thing", "fieldName"=>"legacyMessage"}}]}