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=, included, #metadata

Constructor Details

#initializeField

Returns a new instance of Field.


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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>

Returns Map String argument names to their Argument implementations.

Returns:


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

#complexityNumeric, Proc

Returns The complexity for this field (default: 1), as a constant or a proc like `->(query_ctx, args, child_complexity) { } # Numeric`.

Returns:

  • (Numeric, Proc)

    The complexity for this field (default: 1), as a constant or a proc like `->(query_ctx, args, child_complexity) { } # Numeric`


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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?

Returns The mutation this field was derived from, if it was derived from a mutation.

Returns:


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

#nameString

Returns The name of this field on its ObjectType (or InterfaceType).

Returns:


# 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

Parameters:

  • new_hash_key (Symbol)

    A key to access with `#[key]` to resolve this field. Overrides the existing resolve proc.


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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

Parameters:

  • new_property (Symbol)

    A method to call to resolve this field. Overrides the existing resolve proc.


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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)

Parameters:

  • object (Object)

    The object this field belongs to

  • arguments (Hash)

    Arguments declared in the query

  • context (GraphQL::Query::Context)

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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.

Parameters:

  • new_resolve_proc (<#call(obj, args, ctx)>, nil)

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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