rgviz: A Ruby repository from bradseefeld

Rgviz¶ ↑

This library implements the query language for the Google Visualization API wire protocol.

It can generate an AST of the query from a string. The AST nodes implement the Visitor Pattern so you can easily work with it.

Installation¶ ↑

gem install rgviz

Ruby on Rails¶ ↑

There is a separate project on top of this library called rgviz-rails, check it out!

Usage¶ ↑

First you must require the library:

require 'rubygems'
require 'rgviz'

To parse a query:

query = Rgviz::Parser.parse 'select name where age > 20'

Extensions¶ ↑

If you pass :extensions => true to the parse method these new scalar functions will be available:

concat: converts each of its arguments to a string and then concatenates them. For example: concat(1, '-', '2') returns '1-2'. Can also receive just a single argument to convert it to a string.

So to have this function parsed you need to do:

query = Rgviz::Parser.parse 'select concat(name, age)', :extensions => true

These new functions are not part of Google’s query language, but they are very handy so we added them. These functions are also supported by rgviz-rails.

Using the Visitor Pattern¶ ↑

class MyVisitor < Rgviz::Visitor
  def visit_select(node)
    # do something with the node
    puts 'before select'
    puts node.columns.length

    # returning true means visiting this node children
    true
  end

  def end_visit_select(node)
    # This will be invoked after visiting the node
    puts "after select"
  end

  def visit_id_column(node)
    puts node.name
  end
end

query = Rgviz::Parser.parse 'select name, age'
query.accept MyVisitor.new

# outputs:
# before select
# 2
# name
# age
# after select

There is a visit_XXX and end_visit_XXX for every node in the language.

Wrappers for Google DataTable and others¶ ↑

Their source code is here. You can use them to generate the javascript code to implement the wire protocol.

Output Formatters¶ ↑

You can use Rgviz::HtmlRenderer.render(table) and Rgviz::CsvRenderer.render(table) to get a string to render in html or csv output format.

bradseefeld/rgviz