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.
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 Types::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 = object.comments.featured
if since
comments = comments.where("created_at >= ?", since)
end
# Return an Array or ActiveRecord::Relation
comments
end
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
You can customize connection and edge types by using the class-based API:
# Make an edge class for use in the connection below:
class Types::PostEdgeType < GraphQL::Types::Relay::BaseEdge
node_type(PostType)
end
# Make a customized connection type
class Types::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
Note: If you use classes for an object’s connection or edge types, then all of that object’s connection and edge types should be classes. Otherwise, the auto-generated types from the .edge_type or .connection_type helpers will conflict with the class-based types.
Now, you can use PostConnectionWithTotalCountType to define a connection with the “totalCount” field:
class Types::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.
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.
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 Types::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 Types::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 Types::TeamMembershipsConnectionType < GraphQL::Types::Relay::BaseConnection
# Here, hook up your custom class with `edge_class:`
edge_type(MembershipSinceEdgeType, edge_class: MembershipSinceEdge)
end
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
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.
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