Erlang boss_db hello world?

Question

Recently I tried to install and run a demo of boss_db ORM for Erlang.

Here is what I did:

• clone the repository
• cd boss_db/
• rebar get-deps

• put a simple mydb.erl file into src/:

  -module(mydb).
  
  -compile(export_all).
  
  start() ->
  

  DBOptions = [{adapter, pgsql}, {db_host, "localhost"}, {db_port, 5432}, {db_username, "postgres"}, {db_password, "mypass"},
  {cache_enable, false}, {cache_exp_time, 0}],

  boss_db:start(DBOptions).

• rebar compile

• cd ebin/
• run erl
• mydb:start()

Here is what I get:

** exception exit: shutdown

Whatam I doing wrong here? How is it supposed to be run?

P.S. I tried to run application:start(boss_db) as well, but the result is the same.

P.P.S. I have read the documentation twice, but I still have no idea how to run the whole thing.

Answer 1

git clone git://github.com/evanmiller/boss_db.git
cd boss_db/
rebar get-deps
emacs src/mydb.erl
rebar compile
erl -pa ./ebin ./deps/*/ebin

These steps worked for me. code:is_loaded() will not work right after you run erl. Only when the module is invoked, the code is loaded.

I do get an application shutdown, but it is because the code is trying to connect to a Postgres DB and can't connect to it.

Erlang R15B02 (erts-5.9.2) [source] [smp:8:8] [async-threads:0] [hipe] [kernel-poll:false]

Eshell V5.9.2  (abort with ^G)
1> mydb:start().
** exception exit: shutdown
=ERROR REPORT==== 9-Oct-2012::12:13:07 ===
** Generic server <0.35.0> terminating 
** Last message in was {'EXIT',<0.34.0>,
                        {{badmatch,
                          {error,
                           {{badmatch,
                             {error,
                              {{badmatch,{error,econnrefused}},
                               [{pgsql_sock,init,1,
                                 [{file,"src/pgsql_sock.erl"},{line,51}]},
                                {gen_server,init_it,6,
                                 [{file,"gen_server.erl"},{line,304}]},
                                {proc_lib,init_p_do_apply,3,
                                 [{file,"proc_lib.erl"},{line,227}]}]}}},
                            [{boss_db_controller,init,1,
                              [{file,"src/boss_db_controller.erl"},{line,31}]},
                             {gen_server,init_it,6,
                              [{file,"gen_server.erl"},{line,304}]},
                             {proc_lib,init_p_do_apply,3,
                              [{file,"proc_lib.erl"},{line,227}]}]}}},
                         [{poolboy,new_worker,2,
                           [{file,"src/poolboy.erl"},{line,348}]},
                          {poolboy,prepopulate,4,
                           [{file,"src/poolboy.erl"},{line,370}]},
                          {poolboy,init,2,
                           [{file,"src/poolboy.erl"},{line,74}]},
                          {gen_fsm,init_it,6,
                           [{file,"gen_fsm.erl"},{line,361}]},
                          {proc_lib,init_p_do_apply,3,
                           [{file,"proc_lib.erl"},{line,227}]}]}}
** When Server state == {state,
                            {<0.35.0>,poolboy_sup},
                            simple_one_for_one,
                            [{child,undefined,boss_db_controller,
                                 {boss_db_controller,start_link,
                                     [[{size,5},
                                       {max_overflow,10},
                                       {adapter,pgsql},
                                       {db_host,"localhost"},
                                       {db_port,5432},
                                       {db_username,"postgres"},
                                       {db_password,"mypass"},
                                       {cache_enable,false},
                                       {cache_exp_time,0}]]},
                                 temporary,brutal_kill,worker,
                                 [boss_db_controller]}],
                            {set,0,16,16,8,80,48,
                                {[],[],[],[],[],[],[],[],[],[],[],[],[],[],[],
                                 []},
                                {{[],[],[],[],[],[],[],[],[],[],[],[],[],[],
                                  [],[]}}},
                            0,1,[],poolboy_sup,
                            {boss_db_controller,
                                [{size,5},
                                 {max_overflow,10},
                                 {adapter,pgsql},
                                 {db_host,"localhost"},
                                 {db_port,5432},
                                 {db_username,"postgres"},
                                 {db_password,"mypass"},
                                 {cache_enable,false},
                                 {cache_exp_time,0}]}}
** Reason for termination == 
** {{badmatch,
        {error,
            {{badmatch,
                 {error,
                     {{badmatch,{error,econnrefused}},
                      [{pgsql_sock,init,1,
                           [{file,"src/pgsql_sock.erl"},{line,51}]},
                       {gen_server,init_it,6,
                           [{file,"gen_server.erl"},{line,304}]},
                       {proc_lib,init_p_do_apply,3,
                           [{file,"proc_lib.erl"},{line,227}]}]}}},
             [{boss_db_controller,init,1,
                  [{file,"src/boss_db_controller.erl"},{line,31}]},
              {gen_server,init_it,6,[{file,"gen_server.erl"},{line,304}]},
              {proc_lib,init_p_do_apply,3,
                  [{file,"proc_lib.erl"},{line,227}]}]}}},
    [{poolboy,new_worker,2,[{file,"src/poolboy.erl"},{line,348}]},
     {poolboy,prepopulate,4,[{file,"src/poolboy.erl"},{line,370}]},
     {poolboy,init,2,[{file,"src/poolboy.erl"},{line,74}]},
     {gen_fsm,init_it,6,[{file,"gen_fsm.erl"},{line,361}]},
     {proc_lib,init_p_do_apply,3,[{file,"proc_lib.erl"},{line,227}]}]}

Answer 2

You are not adding dependencies to the code path. That's why an exception is thrown when they are not found. Don't cd into ebin and erl. Instead run

erl -pa ebin -pa deps/*/ebin

from the current directory.

Btw this is not a good way to do this kind of stuff. Instead create a new empty app using rebar. Add boss_db as a dependency to your app in rebar.config. Put your own source files under src. And then

rebar get-deps compile
erl -pa ebin -pa deps/*/ebin