Connections

Relay expresses one-to-many relationships with connections. Connections support pagination, filtering and metadata in a robust way.

graphql-ruby includes built-in connection support for Array, ActiveRecord::Relations, Sequel::Datasets, and Mongoid::Criterias. You can define custom connection classes to expose other collections with GraphQL.

Connection fields

To define a connection field, use the field method. For a return type, get a type’s .connection_type. The field’s method or resolver: should return a collection (eg, Array or ActiveRecord::Relation) without pagination. (The connection will paginate the collection).

For example:

class PostType < GraphQL::Schema::Object
  # `Post#comments` returns an ActiveRecord::Relation
  # The GraphQL field returns a Connection
  field :comments, CommentType.connection_type, null: false
  # `Post#similar_posts` returns an Array
  field :similar_posts, PostType.connection_type, null: false

  # ...
end

(GraphQL-Ruby applies connection logic because the return type’s name ends in Connection. You can manually override this with connection: true or connection: false.)

You can also define custom arguments and a custom resolve function for connections, just like other fields:

field :featured_comments, CommentType.connection_type do
  # Add an argument:
  argument :since, String, required: false
end

def featured_comments(since: nil)
  comments = post.comments.featured
  if since
    comments = comments.where("created_at >= ?", since)
  end
  # Return an Array or ActiveRecord::Relation
  comments
end

Maximum Page Size

You can limit the number of results with max_page_size::

field :featured_comments, CommentType.connection_type, null: false, max_page_size: 50

In addition, you can set a global default for all connection that do not specify a max_page_size:

class MySchema < GraphQL::Schema
  default_max_page_size 100
end

Connection types

You can customize connection and edge types by using the class-based API:

# Make an edge class for use in the connection below:
class PostEdgeType < GraphQL::Types::Relay::BaseEdge
  node_type(PostType)
end

# Make a customized connection type
class PostConnectionWithTotalCountType < GraphQL::Types::Relay::BaseConnection
  edge_type(PostEdgeType)

  field :total_count, Integer, null: false
  def total_count
    # - `object` is the Connection
    # - `object.nodes` is the collection of Posts
    object.nodes.size
  end
end

Now, you can use PostConnectionWithTotalCountType to define a connection with the “totalCount” field:

class AuthorType < GraphQL::Schema::Object
  # Use the custom connection type:
  field :posts, PostConnectionWithTotalCountType, null: false, connection: true
end

(It uses connection: true because the type name doesn’t end in "Connection".)

This way, you can query your custom fields, for example:

{
  author(id: 1) {
    posts {
      totalCount    # <= Your custom field
    }
  }
}

In the same vein, you can extend your *Edge classes with extra fields.

Customizing Base Classes

The provided classes in GraphQL::Types::Relay extend Schema::Object, but if you want to add your own extensions, you can build your own type system using the built-in ones for inspiration.

For example, to make your connection classes extend your own base object, you could add a base connection class to your app:

class Types::BaseConnection < Types::BaseObject
  # ... copy-paste here
end

Then take code from GraphQL::Types::Relay::BaseConnection and adapt it to your app.

You can mix-and-match customized and built-in types. For example, if you customize the base Edge class, you can still use the built-in Types::Relay::PageInfo class.

Custom Edge classes

For more robust custom edges, you can define a custom edge class. It will be obj in the edge type’s resolve function. For example, to define a membership edge:

# Make sure to familiarize yourself with GraphQL::Relay::Edge --
# you have to avoid naming conflicts here!
class MembershipSinceEdge < GraphQL::Relay::Edge
  # Cache `membership` to avoid multiple DB queries
  def membership
    @membership ||= begin
      # "parent" and "node" are passed in from the surrounding Connection,
      # See `Edge#initialize` for details
      person = self.parent
      team = self.node
      Membership.where(person: person, team: team).first
    end
  end

  def member_since
    membership.created_at.to_i
  end

  def leader?
    membership.leader?
  end
end

Then, hook it up with custom edge type and custom connection type:

# Person => Membership => Team
class MembershipSinceEdgeType < GraphQL::Types::Relay::BaseEdge
  node_type(TeamType)

  field :member_since, Integer, null: false,
    description: "The date that this person joined this team"
  field :is_primary, Boolean, null: false,
    description: "Is this person the team leader?",
    method: :primary?
end

class TeamMembershipsConnectionType < GraphQL::Types::Relay::BaseConnection
  # Here, hook up your custom class with `edge_class:`
  edge_type(MembershipSinceEdgeType, edge_class: MembershipSinceEdge)
end

Connection objects

Maybe you need to make a connection object yourself (for example, to return a connection type from a mutation). You can create a connection object like this:

items = [...]     # your collection objects
args = {}         # stub out arguments for this connection object
connection_class = GraphQL::Relay::BaseConnection.connection_for_nodes(items)
connection_class.new(items, args)

.connection_for_nodes will return RelationConnection or ArrayConnection depending on items, then you can make a new connection

For specifying a connection based on an ActiveRecord::Relation or Sequel::Dataset:

object = {}       # your newly created object
items = [...]     # your AR or Sequel collection
args = {}         # stub out arguments for this connection object
items_connection = GraphQL::Relay::RelationConnection.new(
  items,
  args
)
edge = GraphQL::Relay::Edge.new(object, items_connection)

Additionally, connections may be provided with the GraphQL::Field that created them. This may be used for custom introspection or instrumentation. For example,

  Schema.get_field(TodoListType, "todos")
  # => #<GraphQL::Field name="todos">
  context.irep_node.definitions[TodoListType]
  # => #<GraphQL::Field name="todos">
  # although this one may not work with fields on interfaces

Custom connections

You can define a custom connection class and add it to GraphQL::Relay.

First, define the custom connection:

require "set" # From Ruby's standard library
class SetConnection < BaseConnection
  # derive a cursor from `item`
  def cursor_from_node(item)
    # ...
  end

  private
  # apply `#first` & `#last` to limit results
  def paged_nodes
    # ...
  end

  # apply cursor, order, filters, etc
  # to get a subset of matching objects
  def sliced_nodes
    # ...
  end
end

Then, register the new connection with GraphQL::Relay::BaseConnection:

# When exposing a `Set`, use `SetConnection`:
GraphQL::Relay::BaseConnection.register_connection_implementation(Set, SetConnection)

At runtime, GraphQL::Relay will use SetConnection to expose Sets.

Creating connection fields by hand

If you need lower-level access to Connection fields, you can create them programmatically. Given a GraphQL::Field which returns a collection of items, you can turn it into a connection field with ConnectionField.create.

For example, to wrap a field with a connection field:

field = GraphQL::Field.new
# ... define the field
connection_field = GraphQL::Relay::ConnectionField.create(field)

Cursors

By default, cursors are encoded in base64 to make them opaque to a human client. You can specify a custom encoder with Schema#cursor_encoder. The value should be an object which responds to .encode(plain_text, nonce:) and .decode(encoded_text, nonce: false).

For example, to use URL-safe base-64 encoding:

module URLSafeBase64Encoder
  def self.encode(txt, nonce: false)
    Base64.urlsafe_encode64(txt)
  end

  def self.decode(txt, nonce: false)
    Base64.urlsafe_decode64(txt)
  end
end

MySchema = GraphQL::Schema.define do
  # ...
  cursor_encoder(URLSafeBase64Encoder)
end

Now, all connections will use URL-safe base-64 encoding.

From a connection instance, the cursor_encoders methods available via GraphQL::Relay::BaseConnection#encode and GraphQL::Relay::BaseConnection#decode