Class: Pbbuilder

Inherits:
BasicObject
Defined in:
lib/pbbuilder.rb,
lib/pbbuilder/errors.rb,
lib/pbbuilder/railtie.rb,
lib/pbbuilder/collection_renderer.rb

Overview

Pbbuilder makes it easy to create a protobuf message using the builder pattern. It is heavily inspired by jbuilder

Given this example message definition: message Person 

string name = 1;
repeated Person friends = 2;

You can use Pbbuilder as follows:

person = RPC::Person.new

Pbbuilder.new(person) do |pb|

pb.name "Hello"
pb.friends [1, 2, 3] do |number|
  pb.name "Friend ##{number}"
end

end

message.name => “Hello”

It basically works exactly like jbuilder. The main difference is that it can use introspection to figure out what kind of protobuf message it needs to create.

Direct Known Subclasses

PbbuilderTemplate

Defined Under Namespace

Classes: CollectionRenderer, MergeError, Railtie

Instance Method Summary collapse

Constructor Details

#initialize(message) {|_self| ... } ⇒ Pbbuilder

Returns a new instance of Pbbuilder.

Yields:

  • (_self)

Yield Parameters:

  • _self (Pbbuilder) —

    the object that the method was called on



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# File 'lib/pbbuilder.rb', line 33

def initialize(message)
  @message = message

  yield self if ::Kernel.block_given?
end

Dynamic Method Handling

This class handles dynamic methods through the method_missing method

#method_missing ⇒ Object 



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# File 'lib/pbbuilder.rb', line 39

def method_missing(...)
  set!(...)
end

Instance Method Details

#attributes! ⇒ Object 



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# File 'lib/pbbuilder.rb', line 43

def attributes!
  @message.to_h
end

#extract!(element, *args) ⇒ Object

Shorthand command for getting a few attributes from an object.

pb.extract! racer, :name, :id, :age



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# File 'lib/pbbuilder.rb', line 139

def extract!(element, *args)
  args.each { |arg| @message[arg.to_s] = element.send(arg) }
end

#merge!(object) ⇒ Object

Merges object into a protobuf message, mainly used for caching.

Parameters:

  • object (Hash) 


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# File 'lib/pbbuilder.rb', line 146

def merge!(object)
  ::Kernel.raise Pbbuilder::MergeError.build(target!, object) unless object.class == ::Hash

  object.each do |key, value|
    next if value.respond_to?(:empty?) && value.empty?

    descriptor = _descriptor_for_field(key)
    ::Kernel.raise ::ArgumentError, "Unknown field #{key}" if descriptor.nil?

    if descriptor.label == :repeated
      # optional empty fields don't show up in @message object,
      # we recreate empty message, so we can fill it with values
      if @message[key.to_s].nil?
        @message[key.to_s] = _new_message_from_descriptor(descriptor)
      end

      if value.respond_to?(:to_hash)
        value.to_hash.each {|k, v| @message[key.to_s][k] = v}
      elsif value.respond_to?(:to_ary)
        elements = value.map do |obj|
          descriptor.subtype ? descriptor.subtype.msgclass.new(obj) : obj
        end

        @message[key.to_s].replace(elements)
      end
    else
      if descriptor.type == :message
        @message[key.to_s] = descriptor.subtype.msgclass.new(value)
      else
        # pb.fields {"one" => "two"}
        # pb.boolean true || false
        # pb.field_name do
        #    pb.tags ["ok", "cool"]
        # end

        @message[key.to_s] = value
      end
    end
  end
end

#new_message_for(field) ⇒ Object

Parameters:

  • field —

    string



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# File 'lib/pbbuilder.rb', line 193

def new_message_for(field)
  descriptor = _descriptor_for_field(field)
  ::Kernel.raise ::ArgumentError, "Unknown field #{field}" if descriptor.nil?

  _new_message_from_descriptor(descriptor)
end

#respond_to_missing?(field) ⇒ Boolean

Returns:

  • (Boolean) 


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# File 'lib/pbbuilder.rb', line 47

def respond_to_missing?(field)
  !!_descriptor_for_field(field)
end

#set!(field, *args, &block) ⇒ Object

When calling for ex: response.drivers, where response is a Google::Protobuf object, ‘drivers’ is not a method on that. These methods (or messages in our case) get added here. This is of course based on what kind of message it is. Singular, an array (repeated) etc. with their arguments.



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# File 'lib/pbbuilder.rb', line 54

def set!(field, *args, &block)
  name = field.to_s
  descriptor = _descriptor_for_field(name)
  ::Kernel.raise ::ArgumentError, "Unknown field: #{name}" if descriptor.nil?

  # An block is used to pass on it's children
  if ::Kernel.block_given?
    ::Kernel.raise ::ArgumentError, "can't pass block to non-message field" unless descriptor.type == :message

    if descriptor.label == :repeated
      # example syntax that should end up here:
      #    pb.field @array { |element| pb.name element.name }
      ::Kernel.raise ::ArgumentError, "wrong number of arguments #{args.length} (expected 1)" unless args.length == 1
      collection = args.first
      _append_repeated(name, descriptor, collection, &block)
    else
      # example syntax that should end up here:
      #   pb.field { pb.name "hello" }
      ::Kernel.raise ::ArgumentError, "wrong number of arguments (expected 0)" unless args.empty?

      message = (@message[name] ||= _new_message_from_descriptor(descriptor))
      _scope(message, &block)
    end
  # No block given, but with 1 argument
  elsif args.length == 1
    arg = args.first
    if descriptor.label == :repeated
      if arg.respond_to?(:to_hash)
        # example syntax that should end up here:
        #   pb.fields {"one" => "two"}

        arg.to_hash.each { |k, v| @message[name][k] = v }
      elsif arg.respond_to?(:to_ary) && !descriptor.type.eql?(:message)
        # pb.fields ["one", "two"]

        @message[name].replace arg.to_ary
      elsif arg.respond_to?(:to_ary) && descriptor.type.eql?(:message)
        # pb.friends [Person.new(name: "Johnny Test"), Person.new(name: "Max Verstappen")]
        #
        # Accepts both objects that can be to_hash-translated into keyword arguments
        # for creating a nested proto message object and actual proto message objects
        # which can be assigned "as is". With "as-is" assignment the proto message can be stored
        # in memory and reused
        nested_messages = arg.map do |arg_member_message_or_hash|
          # If the arg passed already is a proto message and is the same as the
          # field expects - just use it as-is
          if arg_member_message_or_hash.is_a?(descriptor.subtype.msgclass)
            arg_member_message_or_hash
          else
            descriptor.subtype.msgclass.new(arg_member_message_or_hash)
          end
        end
        @message[name].replace(nested_messages)
      else
        # example syntax that should end up here:
        #   pb.fields "one"
        @message[name].replace [arg]
      end
    else
      # example syntax that should end up here:
      #   pb.field "value"

      @message[name] = arg
    end
  else
    # example syntax that should end up here:
    #   pb.field @value, :id, :name, :url
    element = args.shift
    if descriptor.label == :repeated
      # If the message field that's being assigned is a repeated field, then we assume that `element` is enumerable.
      # This way you can do something like pb.repeated_field @array, :id, :name
      # This will create a message out of every object in @array, copying over the :id and :name values.
      set!(name, element) do |item|
        extract!(item, *args)
      end
    else
      set!(name) do
        extract!(element, *args)
      end
    end
  end
end

#target! ⇒ Object

Returns Initialized message object.

Returns:

  • Initialized message object



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# File 'lib/pbbuilder.rb', line 188

def target!
  @message
end