Linqr - Query Comprehensions for Ruby

Linq ( http://msdn.microsoft.com/en-us/vcsharp/aa336746 )like sytax for ruby.

Linq in C# is a great example of bringing a uniform query model to different sources of Data. Different providers can be hooked into the model so developers can still use the familiar sytax to query the data source instead of learning a whole new api.

Usage

Querying enumerable

• Quering an array

  numbers = [ 5, 4, 1, 3, 9, 8, 6, 7, 2, 0 ]
  output =  _{ 
  from x
  in_ numbers
  where (x == 3 ||  x == 5 || x == 8) && ( x % 2) == 0
  select x * 3
  }
  output.should == [24]
  

• Quering a hash

  hash = {:a => 1 , :b => 2 , :c => 3}
  output = _{
  from k,v
  in_ hash
  where v == 3
  select k
  }
  

  output.should == [:c]

• Grouping(select can select into anonymous types)

  numbers = [ 5, 4, 1, 3, 9, 8, 6, 7, 2, 0 ]
  number_groups = _{
  from n 
  in_ numbers
  where n > 3 && n < 100
  group_by n % 5  => :g
  select :remainder => g.key , :values => g.values
  }
  number_groups.collect(&:remainder).should == [0, 4, 1, 3, 2]
  

• Ordering

  words = [ "cherry", "apple", "blueberry" ]
  sorted_words = _{
  from word 
  in_ words
  order_by word.length
  select word
  }
  sorted_words.should == ["apple", "cherry", "blueberry"]
  

• Selecting into anonymous types

  products = [Product.new("shoes", 1.75), Product.new("glasses", 55.55), Product.new("pencil", 5.20)]
  
  cheap_product_names = _{
  from p
  in_ products 
  where p.price < 10
  select :name => "Cheap - #{p.name}" , :new_price => p.price + 10
  }
  
  cheap_product_names.collect(&:name).should == ["Cheap - shoes","Cheap - pencil"]
  cheap_product_names.collect(&:new_price).should == [11.75, 15.20]
  

Querying ActiveRecord Models

All the examples listed for enumerable should work with activerecord models too

grouped_by_name = _{
    from o 
    in_ Order
    order_by o.name
    group_by o.name   => :g
    select :name => g.key , :orders => g.values
  }

Querying Groupon Api

output =  _{·
  from deal
  in_  GrouponDeals
  where deal.lat == 38.8339 && deal.lng == -104.821·
  select deal
}