基于Cowboy的Erlang服务经rebar3构建后无法访问Mnesia求助

我基于Cowboy构建Erlang服务器，使用jiffy处理JSON数据，目前遇到两个问题：

• 通过rebar3生成的二进制文件启动shell后，Cowboy可正常运行，但无法访问OTP内置的Mnesia；
• 运行rebar3时输出如下错误信息：

There are missing function calls in the release.
===> Make sure all applications needed at runtime are included in the release.
===> db_access:init_tables/0 calls undefined function mnesia:create_table/2
===> db_access:insert_apod_entries/1 calls undefined function mnesia:transaction/1
===> db_access:insert_apod_entries/1 calls undefined function mnesia:write/1

直接执行erl命令启动Erlang时可正常访问Mnesia，我的rebar.config文件内容如下：

%% -*- mode: erlang;erlang-indent-level: 4;indent-tabs-mode: nil -*-
%% ex: ts=4 sw=4 ft=erlang et

%% escript_incl_extra is for internal rebar-private use only.
%% Do not use outside rebar. Config interface is not stable.
{require_erts_vsn, ".*"}.
{require_otp_vsn, ".*"}.
{require_min_otp_vsn, ".*"}.


{escript_incl_extra, [{"priv/templates/*", "."}]}.
{include_src, false}.

{deps, [
    {jiffy, "1.1.1", "deps/"},
    {cowlib,"2.11.0", "deps/"},
    {cowboy, "2.9.0", "deps/"}
]}.

{erl_first_files, ["src/db_access.erl", 
                    "src/tar_watch_handler.erl",
                    "star_watch_server_app.erl",
                    "star_watch_server_sup.erl"
                    ]}.   

% {artifacts, ["/home/oleg/Projects/erlang_practice/star_watch_server/deps/jiffy/priv/jiffy.so"]}.
{plugins, [
    { pc, {git, "git@github.com:blt/port_compiler.git", {branch, "master"}}}
]}.
{overrides,
 [{override, jiffy, [
     {plugins, [pc]},
     {artifacts, ["priv/jiffy.so"]},
     {provider_hooks, [
         {post,
             [
             {compile, {pc, compile}},
             {clean, {pc, clean}}
             ]
          }]
      }
  ]}
]}.

{base_dir, "_build"}.
%% directory in '<base_dir>/<profile>/' where deps go
{deps_dir, "lib"}.
%% where rebar3 operates from; defaults to the current working directory
{root_dir, "."}.
%% where checkout dependencies are to be located
{checkouts_dir, "_checkouts"}.
%% where, under <base_dir>/<profile> checkout dependencies are to be built
{checkouts_out_dir, "checkouts"}.
%% directory in '<base_dir>/<profile>/' where plugins go
{plugins_dir, "plugins"}.
%% directories where OTP applications for the project can be located
{project_app_dirs, ["apps/*", "lib/*", "."]}.
%% Directories where source files for an OTP application can be found
{src_dirs, ["src"]}.
%% Paths to miscellaneous Erlang files to compile for an app
%% without including them in its modules list
{extra_src_dirs, []}.


%% Types dict:dict() and digraph:digraph() have been introduced in Erlang 17.
%% At the same time, their counterparts dict() and digraph() are to be
%% deprecated in Erlang 18. namespaced_types option is used to select proper
%% type name depending on the OTP version used.
{erl_opts,
 [
  {platform_define, "(linux|solaris|freebsd|darwin)", 'HAVE_SENDFILE'},
  {platform_define, "(linux|freebsd)", 'BACKLOG', 128},
  {platform_define, "R13", 'old_inets'},
  {src_dirs, ["src"]}
  ]}.

{minimum_otp_vsn, "25.0.4"}.
{application_resource_extensions, [
    ".app.src.script", ".app.src"
]}.

{cover_enabled, true}.
{validate_app_modules, true}.
{base_dir, "_build"}.
%% directory in '<base_dir>/<profile>/' where deps go
{deps_dir, "lib"}.
%% where rebar3 operates from; defaults to the current working directory
{root_dir, "."}.
%% where checkout dependencies are to be located
{checkouts_dir, "_checkouts"}.
%% where, under <base_dir>/<profile> checkout dependencies are to be built
{checkouts_out_dir, "checkouts"}.




{xref_checks, []}.
{xref_queries,
 [{"(XC - UC) || (XU - X - B
      -("escript":"foldl"/"3")
      -("eunit_test":"function_wrapper"/"2")
      -("eflame":"apply"/"5")
      -("abnfc":"file"/"2")
      -("erlydtl":"compile"/"3")
      -("lfe_comp":"file"/"2")
      -("neotoma":"file"/"2")
      -("protobuffs_compile":"scan_file"/"2")
      -("gpb_compile":"file"/"2")
      -("gpb_compile":"format_error"/"1")
      -("diameter_codegen":"from_dict"/"4")
      -("diameter_dict_util":"format_error"/"1")
      -("diameter_dict_util":"parse"/"2")
      -("erlang":"timestamp"/"0")
      -("rebar_rnd":"seed"/"1")
      -("rebar_rnd":"uniform"/"0"))",
         []}]}.

{dialyzer,
 [
  {plt_extra_apps, [diameter]},
  {warnings,
   [
    unmatched_returns,
    error_handling,
    race_conditions
   ]}
 ]}.

解决方案 #

1. 在应用的.app.src文件中添加Mnesia依赖 #

Rebar3构建发布版本时，只会包含应用声明依赖的OTP应用。你需要在项目的.app.src文件（通常在src目录下，比如star_watch_server.app.src）的applications列表里加入mnesia：

{application, star_watch_server,
 [{description, "Star Watch Server"},
  {vsn, "0.1.0"},
  {modules, [...],
  {registered, [...]},
  {applications, [kernel, stdlib, cowboy, jiffy, mnesia]}, % 此处添加mnesia
  {mod, {star_watch_server_app, []}},
  {env, []}
 ]}.

2. 确保Mnesia在应用启动前初始化 #

如果你的应用需要在启动时使用Mnesia，要在star_watch_server_app.erl的start/2函数中先启动Mnesia，再执行数据库初始化操作：

start(_StartType, _StartArgs) ->
    % 启动Mnesia
    mnesia:start(),
    % 初始化数据表
    db_access:init_tables(),
    % 启动应用监控树
    star_watch_server_sup:start_link().

3. 重新构建发布版本 #

修改配置后，执行以下命令清理并重新构建：

rebar3 clean
rebar3 release

启动生成的发布版本后，即可正常访问Mnesia。

内容的提问来源于stack exchange，提问作者user1553131