From: Ezra Zygmuntowicz <ezmobius@...>
Date: 2006-01-04T03:55:22+09:00
Subject: DSL help?

Hey rubyists-

	I was wondering if someone could help me make this small dsl I wrote  
into a little bit better syntax. The Cond class just takes a block in  
its constructor and converts what's inside the block into an sql  
where clause with ? syntax like this:

c = Cond.new do
   first_name ‘=’, ‘Ezra’
   start_date ‘between’, ‘2006-01-01′, ‘2006-01-30′
   last_name ‘like’, ‘Zyg%’
   sql ‘hosts.id = something.id'
end

p c.where
#=> ["first_name = ? and start_date between ? and ? and last_name  
LIKE ? and hosts.id = something.id", "Ezra", "2006-01-01",  
"2006-01-30", "Zyg%"]

	I would like to be able to get rid of the quotes around the  
operators '=', '<=', 'LIKE' and so on to become =, <= and LIKE . Also  
I would like to be able to get rid of the need for commas inside the  
block as well. Inside of the Cond class initialize method it justs  
uses instance_eval &block to get the block contents and then uses  
method_missing to build a nested array for each statement.

	Anyone have any better ideas to offer on how to make this interface  
a little nicer? Thanks in advance.


  class Cond
     # Uses a block to initialize the condition:
     # c = InVisible::Cond.new do
     #    month '<=', 11
     #    year '=', 2005
     #    name 'LIKE', 'ruby%'
     #  end
     #
     # c.where -> ["month <= ? and year = ? and name LIKE ?", 11,  
2005, "ruby%"]
     #
     # to include direct SQL, use like this:
     # c = InVisible::Cond.new do
     #   sql "hosts.id = logs.host_id and hosts.name", 'like',  
"123.23.45.67"
     # end
     # if a value needs to by typed (f.e. in Postgres: "ip <  
inet ?"), use a form of:
     # c = InVisible::Cond.new do
     #    ip '= inet', '123.34.56.78/24'
     # end
     #
     # to expand an existing condition, use the << method
     # c << ['age', '>', 30]

       def initialize(&block)
         @args = []
         instance_eval(&block) if block_given?
       end

       def method_missing(sym, *args)
           @args << [sym,args.flatten].flatten
       end

       def <<(*args)
          @args << [args.flatten].flatten
       end

       def where(args=@args)
           q = []
           ary = []
           args.each do |pair|
             iv = pair[1..99]
             unless iv.last.nil? || iv.last.to_s == ''
                 if pair[0].to_s =~ /^sql.*/ then
                    pair[0] = iv.shift
                 end
                 case iv.size
                 when 0:
                     q << "#{pair[0]}"   # the case when there is  
only one (sql) statements
                 when 1:
       	            q << "#{pair[0]} = ?"
       	            ary << iv.last
       	        when 2:
       	            operator = iv[0]
       	            q << "#{pair[0]} #{operator} ?"
   	                ary << iv.last
   	            when 3:
   	                op = case iv[0]
                             when 'between': "between ? and ?"
                         end
                     q << "#{pair[0]} #{op}"
                     ary << iv[-2] << iv[-1]
   	            end
       	    end
           end
           return [q.join(" and ")].concat(ary)
       end

  end


Cheers-
-Ezra