Class: GraphQL::Language::Visitor

Inherits:
Object
  • Object
show all
Defined in:
lib/graphql/language/visitor.rb

Overview

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

Examples:

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

Defined Under Namespace

Classes: DeleteNode, NodeVisitor

Constant Summary collapse

SKIP =
Deprecated.

Use super to continue the visit; or don’t call it to halt.

If any hook returns this value, the GraphQL::Language::Visitor stops visiting this node right away

:_skip
DELETE_NODE =

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

DeleteNode.new

Instance Attribute Summary collapse

Class Method Summary collapse

Instance Method Summary collapse

Constructor Details

#initialize(document) ⇒ Visitor

Returns a new instance of Visitor.



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# File 'lib/graphql/language/visitor.rb', line 45

def initialize(document)
  @document = document
  @visitors = {}
  @result = nil
end

Instance Attribute Details

#result ⇒ GraphQL::Language::Nodes::Document (readonly)

Returns The document with any modifications applied.

Returns:



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# File 'lib/graphql/language/visitor.rb', line 52

def result
  @result
end

Class Method Details

.make_visit_methods(ast_node_class) ⇒ Object

We don’t use alias here because it breaks super



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# File 'lib/graphql/language/visitor.rb', line 80

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.
    #
    # For compatibility, it calls hook procs, too.
    # @param node [GraphQL::Language::Nodes::AbstractNode] the node being visited
    # @param parent [GraphQL::Language::Nodes::AbstractNode, nil] the previously-visited node, or `nil` if this is the root node.
    # @return [Array, nil] If there were modifications, it returns an array of new nodes, otherwise, it returns `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
        # Run hooks if there are any
        new_node = node
        no_hooks = !@visitors.key?(node.class)
        if no_hooks || begin_visit(new_node, parent)
          #{
            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
          }
        end
        end_visit(new_node, parent) unless no_hooks

        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

Instance Method Details

#[](node_class) ⇒ NodeVisitor

Deprecated.

see on_ methods, like #on_field

Get a NodeVisitor for node_class

Examples:

Run a hook whenever you enter a new Field

visitor[GraphQL::Language::Nodes::Field] << ->(node, parent) { p "Here's a field" }

Parameters:

  • node_class (Class) —

    The node class that you want to listen to

Returns:



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# File 'lib/graphql/language/visitor.rb', line 61

def [](node_class)
  @visitors[node_class] ||= NodeVisitor.new
end

#on_argument_children(new_node) ⇒ Object 



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# File 'lib/graphql/language/visitor.rb', line 218

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) ⇒ Object 



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# File 'lib/graphql/language/visitor.rb', line 140

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) ⇒ Object 



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# File 'lib/graphql/language/visitor.rb', line 153

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) ⇒ Object Also known as: on_inline_fragment_children 



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# File 'lib/graphql/language/visitor.rb', line 197

def on_fragment_definition_children(new_node)
  new_node = visit_directives(new_node)
  new_node = visit_selections(new_node)
  new_node
end

#on_operation_definition_children(new_node) ⇒ Object 



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# File 'lib/graphql/language/visitor.rb', line 205

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

This method returns an undefined value.

Visit document and all children, applying hooks as you go



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# File 'lib/graphql/language/visitor.rb', line 67

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_directives(new_node) ⇒ Object 



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# File 'lib/graphql/language/visitor.rb', line 166

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) ⇒ Object 



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# File 'lib/graphql/language/visitor.rb', line 177

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