class GraphQL::Language::Visitor

Depth-first traversal through the tree, calling hooks at each stop.

See GraphQL::Language::StaticVisitor for a faster visitor that doesn’t support modifying the document

Examples

Example: Create a visitor counting certain field names

class NameCounter < GraphQL::Language::Visitor
  def initialize(document, field_name)
    super(document)
    @field_name = field_name
    @count = 0
  end

  attr_reader :count

  def on_field(node, parent)
    # if this field matches our search, increment the counter
    if node.name == @field_name
      @count += 1
    end
    # Continue visiting subfields:
    super
  end
end

# Initialize a visitor
visitor = NameCounter.new(document, "name")
# Run it
visitor.visit
# Check the result
visitor.count
# => 3

Constants

DELETE_NODE: When this is returned from a visitor method, Then the node passed into the method is removed from parent‘s children.

Attributes

result [R]

Returns

GraphQL::Language::Nodes::Document — The document with any modifications applied

Public Class Methods

make_visit_methods (ast_node_class)

Source

# File lib/graphql/language/visitor.rb, line 181
      def self.make_visit_methods(ast_node_class)
        node_method = ast_node_class.visit_method
        children_of_type = ast_node_class.children_of_type
        child_visit_method = :"#{node_method}_children"

        class_eval(<<-RUBY, __FILE__, __LINE__ + 1)
          # The default implementation for visiting an AST node.
          # It doesn't _do_ anything, but it continues to visiting the node's children.
          # To customize this hook, override one of its make_visit_methods (or the base method?)
          # in your subclasses.
          #
          # **Parameters**
          #
          # - `node` (`GraphQL::Language::Nodes::AbstractNode`) — the node being visited
          # - `parent` (`GraphQL::Language::Nodes::AbstractNode, nil`) — the previously-visited node, or `nil` if this is the root node.
          #
          # **Returns**
          #
          # - `Array, nil` — If there were modifications, it returns an array of new nodes, otherwise, it returns `nil`.
          #
          # :call-seq:
          #   #{node_method}(GraphQL::Language::Nodes::AbstractNode node, GraphQL::Language::Nodes::AbstractNode | nil parent) -> Array | nil
          def #{node_method}(node, parent)
            if node.equal?(DELETE_NODE)
              # This might be passed to `super(DELETE_NODE, ...)`
              # by a user hook, don't want to keep visiting in that case.
              [node, parent]
            else
              new_node = node
              #{
                if method_defined?(child_visit_method)
                  "new_node = #{child_visit_method}(new_node)"
                elsif children_of_type
                  children_of_type.map do |child_accessor, child_class|
                    "node.#{child_accessor}.each do |child_node|
                      new_child_and_node = #{child_class.visit_method}_with_modifications(child_node, new_node)
                      # Reassign `node` in case the child hook makes a modification
                      if new_child_and_node.is_a?(Array)
                        new_node = new_child_and_node[1]
                      end
                    end"
                  end.join("\n")
                else
                  ""
                end
              }

              if new_node.equal?(node)
                [node, parent]
              else
                [new_node, parent]
              end
            end
          end

          def #{node_method}_with_modifications(node, parent)
            new_node_and_new_parent = #{node_method}(node, parent)
            apply_modifications(node, parent, new_node_and_new_parent)
          end
        RUBY
      end

We don’t use alias here because it breaks super

new (document)

Source

# File lib/graphql/language/visitor.rb, line 48
def initialize(document)
  @document = document
  @result = nil
end

Public Instance Methods

on_argument_children (new_node)

Source

# File lib/graphql/language/visitor.rb, line 156
def on_argument_children(new_node)
  new_node.children.each do |value_node|
    new_child_and_node = case value_node
    when Language::Nodes::VariableIdentifier
      on_variable_identifier_with_modifications(value_node, new_node)
    when Language::Nodes::InputObject
      on_input_object_with_modifications(value_node, new_node)
    when Language::Nodes::Enum
      on_enum_with_modifications(value_node, new_node)
    when Language::Nodes::NullValue
      on_null_value_with_modifications(value_node, new_node)
    else
      raise ArgumentError, "Invariant: unexpected argument value node #{value_node.class} (#{value_node.inspect})"
    end
    # Reassign `node` in case the child hook makes a modification
    if new_child_and_node.is_a?(Array)
      new_node = new_child_and_node[1]
    end
  end
  new_node
end

on_document_children (document_node)

Source

# File lib/graphql/language/visitor.rb, line 78
def on_document_children(document_node)
  new_node = document_node
  document_node.children.each do |child_node|
    visit_method = :"#{child_node.visit_method}_with_modifications"
    new_child_and_node = public_send(visit_method, child_node, new_node)
    # Reassign `node` in case the child hook makes a modification
    if new_child_and_node.is_a?(Array)
      new_node = new_child_and_node[1]
    end
  end
  new_node
end

on_field_children (new_node)

Source

# File lib/graphql/language/visitor.rb, line 91
def on_field_children(new_node)
  new_node.arguments.each do |arg_node| # rubocop:disable Development/ContextIsPassedCop
    new_child_and_node = on_argument_with_modifications(arg_node, new_node)
    # Reassign `node` in case the child hook makes a modification
    if new_child_and_node.is_a?(Array)
      new_node = new_child_and_node[1]
    end
  end
  new_node = visit_directives(new_node)
  new_node = visit_selections(new_node)
  new_node
end

on_fragment_definition_children (new_node)

Source

# File lib/graphql/language/visitor.rb, line 135
def on_fragment_definition_children(new_node)
  new_node = visit_directives(new_node)
  new_node = visit_selections(new_node)
  new_node
end

Also aliased as: on_inline_fragment_children

on_inline_fragment_children (new_node)

Alias for: on_fragment_definition_children

on_operation_definition_children (new_node)

Source

# File lib/graphql/language/visitor.rb, line 143
def on_operation_definition_children(new_node)
  new_node.variables.each do |arg_node|
    new_child_and_node = on_variable_definition_with_modifications(arg_node, new_node)
    # Reassign `node` in case the child hook makes a modification
    if new_child_and_node.is_a?(Array)
      new_node = new_child_and_node[1]
    end
  end
  new_node = visit_directives(new_node)
  new_node = visit_selections(new_node)
  new_node
end

visit() → void

Source

# File lib/graphql/language/visitor.rb, line 66
def visit
  # `@document` may be any kind of node:
  visit_method = :"#{@document.visit_method}_with_modifications"
  result = public_send(visit_method, @document, nil)
  @result = if result.is_a?(Array)
    result.first
  else
    # The node wasn't modified
    @document
  end
end

Visit document and all children

Returns

void

visit_directives (new_node)

Source

# File lib/graphql/language/visitor.rb, line 104
def visit_directives(new_node)
  new_node.directives.each do |dir_node|
    new_child_and_node = on_directive_with_modifications(dir_node, new_node)
    # Reassign `node` in case the child hook makes a modification
    if new_child_and_node.is_a?(Array)
      new_node = new_child_and_node[1]
    end
  end
  new_node
end

visit_selections (new_node)

Source

# File lib/graphql/language/visitor.rb, line 115
def visit_selections(new_node)
  new_node.selections.each do |selection|
    new_child_and_node = case selection
    when GraphQL::Language::Nodes::Field
      on_field_with_modifications(selection, new_node)
    when GraphQL::Language::Nodes::InlineFragment
      on_inline_fragment_with_modifications(selection, new_node)
    when GraphQL::Language::Nodes::FragmentSpread
      on_fragment_spread_with_modifications(selection, new_node)
    else
      raise ArgumentError, "Invariant: unexpected field selection #{selection.class} (#{selection.inspect})"
    end
    # Reassign `node` in case the child hook makes a modification
    if new_child_and_node.is_a?(Array)
      new_node = new_child_and_node[1]
    end
  end
  new_node
end