It's things like this that make Ruby fun :)

query.rb

class Query
  def initialize
    @hash = {}
  end

  def method_missing(name, *args)
    value = args.length > 0 ? args.first : true
    @hash.merge!(name => value)
    self
  end

  def to_hash
    @hash.dup
  end
end

puts Query.new.male.from('baltimore').age(greater_than: 21).in([21230, 21210]).to_hash.inspect
 # => {:male=>true, :from=>"baltimore", :age=>{:greater_than=>21}, :in=>[21230, 21210]}