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, #metadata, #redefine

Constructor Details

#initializeField

Returns a new instance of Field


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# File 'lib/graphql/field.rb', line 151

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:


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# File 'lib/graphql/field.rb', line 142

def arguments
  @arguments
end

#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 151

def complexity
  @complexity
end

#deprecation_reasonObject

Returns the value of attribute deprecation_reason


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# File 'lib/graphql/field.rb', line 129

def deprecation_reason
  @deprecation_reason
end

#descriptionObject

Returns the value of attribute description


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# File 'lib/graphql/field.rb', line 129

def description
  @description
end

#hash_keyObject

Returns the value of attribute hash_key


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# File 'lib/graphql/field.rb', line 129

def hash_key
  @hash_key
end

#mutationGraphQL::Relay::Mutation?

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

Returns:


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# File 'lib/graphql/field.rb', line 145

def mutation
  @mutation
end

#nameString

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

Returns:


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# File 'lib/graphql/field.rb', line 139

def name
  @name
end

#propertyObject

Returns the value of attribute property


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# File 'lib/graphql/field.rb', line 129

def property
  @property
end

#resolve_procObject (readonly)

Returns the value of attribute resolve_proc


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# File 'lib/graphql/field.rb', line 137

def resolve_proc
  @resolve_proc
end

Instance Method Details

#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 164

def resolve(object, arguments, context)
  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 171

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

#to_sObject


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# File 'lib/graphql/field.rb', line 209

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 181

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

#type=(new_return_type) ⇒ Object


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# File 'lib/graphql/field.rb', line 175

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