Getting started

The quickest way to start experimenting with Bmg is to create a simple script and set up a relation.

my_bmg_script.rb

require 'bundler/inline'

gemfile do
  source 'https://rubygems.org'
  gem 'bmg'
  gem 'json'
end

suppliers = Bmg::Relation.new([
  { sid: "S1", name: "Smith", status: 20, city: "London" },
  { sid: "S2", name: "Jones", status: 10, city: "Paris"  },
  { sid: "S3", name: "Blake", status: 30, city: "Paris"  },
  { sid: "S4", name: "Clark", status: 20, city: "London" },
  { sid: "S5", name: "Adams", status: 30, city: "Athens" }
])

by_city = suppliers
  .exclude(status: 30)
  .extend(upname: ->(t){ t[:name].upcase })
  .group([:sid, :name, :upname, :status], :suppliers_in)

puts JSON.pretty_generate(by_city)

This script will output:

[
  {
    "city": "London",
    "suppliers_in": [
      {
        "sid": "S1",
        "name": "Smith",
        "status": 20,
        "upname": "SMITH"
      },
      {
        "sid": "S4",
        "name": "Clark",
        "status": 20,
        "upname": "CLARK"
      }
    ]
  },
  {
    "city": "Paris",
    "suppliers_in": [
      {
        "sid": "S2",
        "name": "Jones",
        "status": 10,
        "upname": "JONES"
      }
    ]
  }
]

Here, we created a relation from an array of hashes. Relations can in fact be created using any Enumerable which yields hashes.