@type complexity_t() ::
  (%{required(atom()) => any()}, non_neg_integer() -> non_neg_integer())
  | (%{required(atom()) => any()}, non_neg_integer(), Absinthe.Complexity.t() ->
       non_neg_integer())
  | {module(), atom()}
  | non_neg_integer()

A complexity function.

See the Absinthe.Type.Field/t explanation of :complexity for more information.

@type custom_error() ::
  %{:message => error_message(), optional(atom()) => serializable()}
  | Keyword.t()

A custom error may be a map or a Keyword.t, but must contain a :message key.

Note that the values that make up a custom error must be serializable.

@type error_message() :: String.t()

An error message is a human-readable string describing the error that occurred.

@type error_value() ::
  error_message()
  | custom_error()
  | [error_message() | custom_error()]
  | serializable()

An error value is a simple error message, a custom error, or a list of either/both of them.

@type resolver_t() ::
  (Absinthe.Resolution.arguments(), Absinthe.Resolution.t() -> result())
  | (Absinthe.Resolution.source(),
     Absinthe.Resolution.arguments(),
     Absinthe.Resolution.t() ->
       result())
  | {module(), atom()}

A resolver function.

See the Absinthe.Type.Field.t explanation of :resolve for more information.

@type result() :: ok_result() | error_result() | middleware_result()

The result of a resolver.

@type serializable() :: any()

Any serializable value.

@type t() :: %Absinthe.Type.Field{
  __private__: Keyword.t(),
  __reference__: Absinthe.Type.Reference.t(),
  args: %{required(binary() | atom()) => Absinthe.Type.Argument.t()} | nil,
  complexity: complexity_t() | nil,
  config: term(),
  default_value: any(),
  definition: module(),
  deprecation: Absinthe.Type.Deprecation.t() | nil,
  description: binary() | nil,
  identifier: atom(),
  middleware: [],
  name: binary(),
  triggers: term(),
  type: Absinthe.Type.identifier_t()
}

The configuration for a field.

• :name - The name of the field, usually assigned automatically by the Absinthe.Schema.Notation.field/4. Including this option will bypass the snake_case to camelCase conversion.
• :description - Description of a field, useful for introspection.
• :deprecation - Deprecation information for a field, usually set-up using Absinthe.Schema.Notation.deprecate/1.
• :type - The type the value of the field should resolve to
• :args - The arguments of the field, usually created by using Absinthe.Schema.Notation.arg/2.
• :resolve - The resolution function. See below for more information.
• :complexity - The complexity function. See below for more information.
• :default_value - The default value of a field. Note this is not used during resolution; only fields that are part of an Absinthe.Type.InputObject should set this value.

Resolution Functions

Default

If no resolution function is given, the default resolution function is used, which is roughly equivalent to this:

{:ok, Map.get(parent_object, field_name)}

This is commonly use when listing the available fields on a Absinthe.Type.Object that models a data record. For instance:

object :person do
  description "A person"

  field :first_name, :string
  field :last_name, :string
end

Custom Resolution

When accepting arguments, however, you probably need to use them for something. Here's an example of defining a field that looks up a list of users for a given location_id:

query do
  field :users, :person do
    arg :location_id, non_null(:id)

    resolve fn %{location_id: id}, _ ->
      {:ok, MyApp.users_for_location_id(id)}
    end
  end
end

Custom resolution functions are passed two arguments:

1. A map of the arguments for the field, filled in with values from the provided query document/variables.
2. An Absinthe.Resolution struct, containing the execution environment for the field (and useful for complex resolutions using the resolved source object, etc)

Complexity function

Default

If no complexity function is given, the default complexity function is used, which is equivalent to:

fn(_, child_complexity) -> 1 + child_complexity end

Custom Complexity

When accepting arguments, however, you probably need to use them for something. Here's an example of defining a field that looks up at most limit users:

query do
  field :users, :person do
    arg :limit, :integer

    complexity fn %{limit: limit}, child_complexity ->
      10 + limit * child_complexity
    end
  end
end

An optional third argument, Absinthe.Complexity struct, provides extra information. Here's an example of changing the complexity using the context:

query do
  field :users, :person do
    arg :limit, :integer

    complexity fn _, child_complexity, %{context: %{admin: admin?}} ->
      if admin?, do: 0, else: 10 + limit * child_complexity
    end
  end
end

Custom complexity functions are passed two or three arguments:

1. A map of the arguments for the field, filled in with values from the provided query document/variables.
2. A non negative integer, which is total complexity of the child fields.
3. An Absinthe.Complexity struct with information about the context of the field. This argument is optional when using an anonymous function.

Alternatively complexity can be an integer greater than or equal to 0:

query do
  field :users, :person do
    complexity 10
  end
end