Introduction

Object fields expose data about that object or connect the object to other objects. You can add fields to your object types with the field(...) class method, for example:

field :name, String, "The unique name of this list", null: false

Objects and Interfaces have fields.

The different elements of field definition are addressed below:

Field Return Type

The second argument to field(...) is the return type. This can be:

Nullability is expressed with the required null: keyword:

Additionally, list types maybe nullable by adding [..., null: true] to the definition.

Here are some examples:

field :name, String, null: true # `String`, may return a `String` or `nil`
field :id, ID, null: false # `ID!`, always returns an `ID`, never `nil`
field :teammates, [Types::User], null: false # `[User!]!`, always returns a list containing `User`s
field :scores, [Integer, null: true], null: true # `[Int]`, may return a list or `nil`, the list may contain a mix of `Integer`s and `nil`s

Field Documentation

Fields maybe documented with a description and may be deprecated.

Descriptions can be added with the field(...) method as a positional argument, a keyword argument, or inside the block:

# 3rd positional argument
field :name, String, "The name of this thing", null: false

# `description:` keyword
field :name, String, null: false,
  description: "The name of this thing"

# inside the block
field :name, String, null: false do
  description "The name of this thing"
end

Deprecated fields can be marked by adding a deprecation_reason: keyword argument:

field :email, String, null: true,
  deprecation_reason: "Users may have multiple emails, use `User.emails` instead."

Fields with a deprecation_reason: will appear as “deprecated” in GraphiQL.

Field Resolution

In general, fields return Ruby values corresponding to their GraphQL return types. For example, a field with the return type String should return a Ruby string, and a field with the return type [User!]! should return a Ruby array with zero or more User objects in it.

By default, fields return values by:

The method name or hash key corresponds to the field name, so in this example:

field :top_score, Integer, null: false

The default behavior is to look for a #top_score method, or lookup a Hash key, :top_score (symbol) or "top_score" (string).

You can override the method name with the method: keyword, or override the hash key with the hash_key: keyword, for example:

# Use the `#best_score` method to resolve this field
field :top_score, Integer, null: false,
  method: :best_score

# Lookup `hash["allPlayers"]` to resolve this field
field :players, [User], null: false,
  hash_key: "allPlayers"

If you don’t want to delegate to the underlying object, you can define a method for each field:

# Use the custom method below to resolve this field
field :total_games_played, Integer, null: false

def total_games_played
  object.games.count
end

Inside the method, you can access some helper methods:

Additionally, when you define arguments (see below), they’re passed to the method definition, for example:

# Call the custom method with incoming arguments
field :current_winning_streak, Integer, null: false do
  argument :include_ties, Boolean, required: false, default_value: false
end

def current_winning_streak(include_ties:)
  # Business logic goes here
end

Field Arguments

Arguments allow fields to take input to their resolution. For example:

Read more in the Arguments guide

Extra Field Metadata

Inside a field method, you can access some low-level objects from the GraphQL-Ruby runtime. Be warned, these APIs are subject to change, so check the changelog when updating.

A few extras are available:

To inject them into your field method, first, add the extras: option to the field definition:

field :my_field, String, null: false, extras: [:ast_node]

Then add ast_node: keyword to the method signature:

def my_field(ast_node:)
  # ...
end

At runtime, the requested runtime object will be passed to the field.

Custom extras are also possible. Any method on your field class can be passed to extras: [...], and the value will be injected into the method. For example, extras: [:owner] will inject the object type who owns the field. Any new methods on your custom field class may be used, too.

Field Parameter Default Values

The field method requires you to pass null: keyword argument to determine whether the field is nullable or not. Another field you may want to overrid is camelize, which is true by default. You can override this behavior by adding a custom field.

class CustomField < GraphQL::Schema::Field
  # Add `null: false` and `camelize: false` which provide default values
  # in case the caller doesn't pass anything for those arguments.
  # **kwargs is a catch-all that will get everything else
  def initialize(*args, null: false, camelize: false, **kwargs, &block)
    # Then, call super _without_ any args, where Ruby will take
    # _all_ the args originally passed to this method and pass it to the super method.
    super
  end
end