From Rails to Erlyweb - Part II

Updated May 2: erlweb:compile(AppDir::string(), Options::[option()]) has option: {auto_compile, Val}, where Val is 'true', or 'false'. In case of development, you can turn on {auto_compile, true}. So, you only need to run erlyweb_app:boot(myapp) once.

2. Manage project

Erlyweb provides erlyweb:compile(App, ..) to compile the source files under app directory. To start an app, you usually should erlydb:start(mysql, ....) and compile app files first. To make life easy, you can put some scripting like code under myproject\script directory. Here's my project source tree:

myproject
  + apps
  |   + myapp
  |       + ebin   
  |       + include
  |       + nbproject
  |       + src
  |           + components
  |           + lib
  |           + services
  |       + test
  |       + www
  + config
  |   * yaws.conf
  + script
      + ebin
      * erlyweb_app.erl

Where, config/yaws.conf contains the configuration that will copy/paste to your real yaws.conf file. Here's mine:

## This is the configuration of apps that will copy/paste to your yaws.conf.

ebin_dir = D:/myapp/trunk/script/ebin
ebin_dir = D:/myapp/trunk/apps/myapp/ebin

<server localhost>
  port = 8000
  listen = 0.0.0.0
  docroot = D:/myapp/trunk/apps/myapp/www
  appmods = </myapp, erlyweb>
  <opaque>
    appname = myapp
  </opaque>
</server>

You may have noticed, all beams under D:/myapp/trunk/script/ebin and D:/myapp/trunk/apps/myapp/ebin will be auto-loaded by yaws.

erlyweb_app.erl is the boot scripting code, which will be used to start db connection and compile the code. Currently I run these scripts manually. I'll talk later.

-module(erlyweb_app).

-export([main/1, boot/1, build/1, start_db/0]).

main([AppName]) ->
    boot(AppName); 
main(_) ->
    usage().

boot(AppName) ->
    build(AppName, true).

build(AppName) ->
    build(AppName, false).

build(AppName, AutoCompile) when is_atom(AppName) ->
    build(atom_to_list(AppName), AutoCompile);
build(AppName, AutoCompile) when is_list(AppName) ->
    start_db(),
    compile(AppName, [debug_info, {auto_compile, AutoCompile}]).

start_db() ->
    erlydb:start(
        mysql, 
        [{hostname, "localhost"},
         {username, "mememe"},
         {password, "uuu"},
         {database, "myapp_dev"}]).
        
compile(AppName, Options) ->
    erlyweb:compile(
        "./apps/" ++ AppName,
        [{erlydb_driver, mysql}] ++ Options).

usage() ->
    io:format("usage: erlyweb_app AppName\n"),
    halt(1).

So, I start myapp by steps:

cd \myproject
yaws -i -sname yaws
1> erlyweb_app:build(myapp).

The erlyweb_app.erl is almost escript ready, but I use it as module functions currently. It's pre-compiled and erlyweb_app.beam is placed under script/ebin

After I made changes to myapp, I run above erlyweb_app:build(myapp). again, then everything is up to date.

This is surely not the best way to handle the write-compile-run-test cycle, I'll improve the scripting to let starting yaws as a node, then hot-swap the compiled code to it.

Comparing to Rails, the Erlyweb project management needs improvement, such as store the database configuration in a plain environment file, and auto load it etc.

It's a good experience to play with Rails, I like rake db:migrate, script, config folders of Rails. And Grails also brings some good idea to manage web app project tree. I'll try to bring them into project manager of ErlyBird.

Next part, I'll talk about the magic behind Erlyweb, and why I prefer the magic of Erlang to Ruby's.