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ref: work-0 tags: ocaml mysql programming functional date: 07-03-2009 19:16 gmt revision:2 [1] [0] [head]

Foe my work I store a lot of analyzed data in SQL databases. In one of these, I have stored the anatomical target that the data was recorded from - namely, STN or VIM thalamus. After updating the analysis programs, I needed to copy the anatomical target data over to the new SQL tables. Where perl may have been my previous go-to language for this task, I've had enuogh of its strange quiks, hence decided to try it in Ruby (worked, but was not so elegant, as I don't actually know Ruby!) and then Ocaml.

ocaml
#use "topfind"
#require "mysql"

(* this function takes a query and a function that converts entries 
in a row to Ocaml tuples *)
let read_table db query rowfunc =
	let r = Mysql.exec db query in
	let col = Mysql.column r in
	let rec loop = function
		| None      -> []
		| Some x    -> rowfunc col x :: loop (Mysql.fetch r)
	in
	loop (Mysql.fetch r)
	;;
	

let _ = 
	let db = Mysql.quick_connect ~host:"crispy" ~database:"turner" ~password:"" ~user:"" () in
	let nn = Mysql.not_null in
	(* this function builds a table of files (recording sessions) from a given target, then 
	uses the mysql UPDATE command to propagate to the new SQL database. *)
	let propagate targ = 
		let t = read_table db 
			("SELECT file, COUNT(file) FROM `xcor2` WHERE target='"^targ^"' GROUP BY file")
			(fun col row -> (
				nn Mysql.str2ml (col ~key:"file" ~row), 
				nn Mysql.int2ml (col ~key:"COUNT(file)" ~row) )
			)
		in
		List.iter (fun (fname,_) -> 
			let query = "UPDATE `xcor3` SET `target`='"^targ^
				"' WHERE STRCMP(`file`,'"^fname^"')=0" in
			print_endline query ;
			ignore( Mysql.exec db query )
		) t ;
	in
	propagate "STN" ; 
	propagate "VIM" ; 
	propagate "CTX" ; 
	Mysql.disconnect db ;;

Interacting with MySQL is quite easy with Ocaml - though the type system adds a certain overhead, it's not too bad.