Class: GraphQL::Field

Inherits:
Object
  • Object
show all
Includes:
Define::InstanceDefinable
Defined in:
lib/graphql/field.rb,
lib/graphql/field/resolve.rb

Overview

Fields belong to ObjectTypes and InterfaceTypes.

They're usually created with the field helper. If you create it by hand, make sure #name is a String.

A field must have a return type, but if you want to defer the return type calculation until later, you can pass a proc for the return type. That proc will be called when the schema is defined.

For complex field definition, you can pass a block to the field helper, eg field :name do ... end. This block is equivalent to calling GraphQL::Field.define { ... }.

Resolve

Fields have resolve functions to determine their values at query-time. The default implementation is to call a method on the object based on the field name.

You can specify a custom proc with the resolve helper.

There are some shortcuts for common resolve implementations:

  • Provide property: to call a method with a different name than the field name
  • Provide hash_key: to resolve the field by doing a key lookup, eg obj[:my_hash_key]

Arguments

Fields can take inputs; they're called arguments. You can define them with the argument helper.

They can have default values which will be provided to resolve if the query doesn't include a value.

Only certain types maybe used for inputs:

  • Scalars
  • Enums
  • Input Objects
  • Lists of those types

Input types may also be non-null -- in that case, the query will fail if the input is not present.

Complexity

Fields can have complexity values which describe the computation cost of resolving the field. You can provide the complexity as a constant with complexity: or as a proc, with the complexity helper.

Examples:

Lazy type resolution

# If the field's type isn't defined yet, you can pass a proc
field :city, -> { TypeForModelName.find("City") }

Defining a field with a block

field :city, CityType do
  # field definition continues inside the block
end

Create a field which calls a method with the same name.

GraphQL::ObjectType.define do
  field :name, types.String, "The name of this thing "
end

Create a field that calls a different method on the object

GraphQL::ObjectType.define do
  # use the `property` keyword:
  field :firstName, types.String, property: :first_name
end

Create a field looks up with [hash_key]

GraphQL::ObjectType.define do
  # use the `hash_key` keyword:
  field :firstName, types.String, hash_key: :first_name
end

Create a field with an argument

field :students, types[StudentType] do
  argument :grade, types.Int
  resolve ->(obj, args, ctx) {
    Student.where(grade: args[:grade])
  }
end

Argument with a default value

field :events, types[EventType] do
  # by default, don't include past events
  argument :includePast, types.Boolean, default_value: false
  resolve ->(obj, args, ctx) {
    args[:includePast] # => false if no value was provided in the query
    # ...
  }
end

Custom complexity values

# Complexity can be a number or a proc.

# Complexity can be defined with a keyword:
field :expensive_calculation, !types.Int, complexity: 10

# Or inside the block:
field :expensive_calculation_2, !types.Int do
  complexity ->(ctx, args, child_complexity) { ctx[:current_user].staff? ? 0 : 10 }
end

Calculating the complexity of a list field

field :items, types[ItemType] do
  argument :limit, !types.Int
  # Mulitply the child complexity by the possible items on the list
  complexity ->(ctx, args, child_complexity) { child_complexity * args[:limit] }
end

Creating a field, then assigning it to a type

name_field = GraphQL::Field.define do
  name("Name")
  type(!types.String)
  description("The name of this thing")
  resolve ->(object, arguments, context) { object.name }
end

NamedType = GraphQL::ObjectType.define do
  # The second argument may be a GraphQL::Field
  field :name, name_field
end

Defined Under Namespace

Modules: Resolve

Instance Attribute Summary collapse

Instance Method Summary collapse

Methods included from Define::InstanceDefinable

#define, #definition_proc=, #metadata

Constructor Details

#initializeField


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# File 'lib/graphql/field.rb', line 147

def initialize
  @complexity = 1
  @arguments = {}
  @resolve_proc = build_default_resolver
end

Instance Attribute Details

#argumentsHash<String => GraphQL::Argument>


# File 'lib/graphql/field.rb', line 138

#complexityNumeric, Proc


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# File 'lib/graphql/field.rb', line 147

def initialize
  @complexity = 1
  @arguments = {}
  @resolve_proc = build_default_resolver
end

#mutationGraphQL::Relay::Mutation?


# File 'lib/graphql/field.rb', line 141

#nameString


# File 'lib/graphql/field.rb', line 135

#resolve_procObject (readonly)

Returns the value of attribute resolve_proc


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# File 'lib/graphql/field.rb', line 133

def resolve_proc
  @resolve_proc
end

Instance Method Details

#hash_key=(new_hash_key) ⇒ Object


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# File 'lib/graphql/field.rb', line 208

def hash_key=(new_hash_key)
  ensure_defined
  @hash_key = new_hash_key
  self.resolve = nil # reset resolve proc
end

#property=(new_property) ⇒ Object


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# File 'lib/graphql/field.rb', line 201

def property=(new_property)
  ensure_defined
  @property = new_property
  self.resolve = nil # reset resolve proc
end

#resolve(object, arguments, context) ⇒ Object

Get a value for this field

Examples:

resolving a field value

field.resolve(obj, args, ctx)

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# File 'lib/graphql/field.rb', line 160

def resolve(object, arguments, context)
  ensure_defined
  resolve_proc.call(object, arguments, context)
end

#resolve=(new_resolve_proc) ⇒ Object

Provide a new callable for this field's resolve function. If nil, a new resolve proc will be build based on its #name, #property or #hash_key.


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# File 'lib/graphql/field.rb', line 168

def resolve=(new_resolve_proc)
  ensure_defined
  @resolve_proc = new_resolve_proc || build_default_resolver
end

#to_sObject


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# File 'lib/graphql/field.rb', line 214

def to_s
  "<Field name:#{name || "not-named"} desc:#{description} resolve:#{resolve_proc}>"
end

#typeObject

Get the return type for this field.


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# File 'lib/graphql/field.rb', line 180

def type
  @clean_type ||= begin
    ensure_defined
    GraphQL::BaseType.resolve_related_type(@dirty_type)
  end
end

#type=(new_return_type) ⇒ Object


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# File 'lib/graphql/field.rb', line 173

def type=(new_return_type)
  ensure_defined
  @clean_type = nil
  @dirty_type = new_return_type
end