Erlang 无法连接到 mysql/mariadb

Question

我无法使用 erlang 连接到 mysql/mariadb。

根据此 github 页的要求： https://github.com/mysql-otp/mysql-otp

要求：

Erlang/OTP version R16B or later
MySQL database version 4.1 or later or MariaDB
GNU Make or Rebar or any other tool for building Erlang/OTP applications

版本：

14> erlang:system_info(otp_release).
"22"

我不确定是否还需要这个要求，但我添加了这个：

[mysqld] default_authentication_plugin=mysql_native_password

到我的 /etc/my.cnf。但这可能无关紧要，因为错误是未定义的函数。我可以编译代码，但我不能运行。非常感谢任何有助于使这项工作正常进行的帮助。

代码：

-module(mydatabase).
-compile(export_all).

connect_to_database() -> 
Conn = mysql:start_link([{host, "localhost"}, {user, "user"},
                       {password, "password"}, {database, "MyDatabase"}]) ,
           
  case Conn of
      {ok, Pid} -> io:fwrite("~w~w~n", [ok,Pid]);
      {error, ConnErr}  -> io:fwrite("error : ~p ~n", [ConnErr])
    end.
              
 start() -> connect_to_database().

mariadb 是运行宁:

sudo systemctl status mariadb
[sudo] password for user: 
● mariadb.service - MariaDB 10.4.13 database server
   Loaded: loaded (/usr/lib/systemd/system/mariadb.service; disabled; vendor >
   Active: active (running) since Sun 2020-06-28 15:33:50 CEST; 1h 4min ago

错误信息：

12> c(mydatabase).     
mydatabase.erl:2: Warning: export_all flag enabled - all functions will be exported
{ok,mydatabase}
13> mydatabase:start().
** exception error: undefined function mysql:start_link/1
 in function  mydatabase:connect_to_database/0 (mydatabase.erl, line 1

Answer 1

您忘记了这个要求：

GNU Make or Rebar or any other tool for building Erlang/OTP applications

根据 mysql-otp docs:

MySQL/OTP is a driver for connecting Erlang/OTP applications to MySQL and MariaDB databases.

OTP application 需要特定的体系结构，mysql 驱动程序需要在应用程序中列为依赖项。您的错误是由于 Erlang 中没有名为 mysql:start_link/1 的函数。相反，这是您的代码必须以某种方式访问的第三方功能，因此文档中的 Usage as a Dependency 部分。

可以使用以下步骤创建一个 OTP application，它使用 mysql/mariaDB 作为依赖项：

Install rebar3.

创建一个 rebar3 app:

~/erlang_programs/mysql1$ rebar3 new app myapp
===> Writing myapp/src/myapp_app.erl
===> Writing myapp/src/myapp_sup.erl
===> Writing myapp/src/myapp.app.src
===> Writing myapp/rebar.config
===> Writing myapp/.gitignore
===> Writing myapp/LICENSE
===> Writing myapp/README.md

在rebar.config文件中添加mysql-otp作为依赖：

  ~/erlang_programs/mysql1$ cd myapp
  ~/erlang_programs/mysql1/myapp$ ls
  LICENSE       rebar.config
  README.md src

像这样：

    {erl_opts, [debug_info]}.
    {deps, [

      {mysql, ".*", {
                      git, "https://github.com/mysql-otp/mysql-otp",
                      {tag, "1.6.0"}
                    }
      }

    ]}.

    {shell, [
      % {config, "config/sys.config"},
        {apps, [myapp]}
    ]}.

将您的源代码放在 src 目录中：

 ~/erlang_programs/mysql1/myapp$ cd src
 ~/erlang_programs/mysql1/myapp/src$ ls
 my_mysql.erl    myapp_app.erl
 myapp.app.src   myapp_sup.erl

my_mysql.erl:

-module(my_mysql).
-compile(export_all).

do_mysql(Name, Info) ->
    {ok, MysqlPid} = mysql:start_link(
                  [{host, "localhost"}, 
                   {user, "root"},
                   {password, ""}, 
                   {database, "mydb"}
                  ]
                ),

     ok = mysql:query(
           MysqlPid, 
           "INSERT INTO people (name, info) VALUES (?, ?)", [Name, Info]
        ),

     {ok, ColumnNames, Rows} = mysql:query(
                MysqlPid, 
                <<"SELECT * FROM people">>),

     io:format("ColumnNames: ~p~nRows: ~p~n", [ColumnNames, Rows]).

获取依赖项并编译所有源代码：

 ~/erlang_programs/mysql1/myapp$ rebar3 compile
 ===> Verifying dependencies...
 ===> Fetching mysql ({git,"https://github.com/mysql-otp/mysql-otp",
                                  {tag,"1.6.0"}})
 ===> Compiling mysql
 ===> Compiling myapp
 src/my_mysql.erl:2: Warning: export_all flag enabled - all functions will be exported

启动 shell 并自动构建所有 .beam 文件的路径（在 rebar3 放置它们的深层嵌套目录中）：

 ~/erlang_programs/mysql1/myapp$ rebar3 shell
 ===> Verifying dependencies...
 ===> Compiling myapp
 Erlang/OTP 20 [erts-9.3] [source] [64-bit] [smp:4:4] [ds:4:4:10] [async-threads:1] [hipe] [kernel-poll:false]

 ===> The rebar3 shell is a development tool; to deploy applications in production, consider using releases (http://www.rebar3.org/docs/releases)
 ===> Booted myapp
 Eshell V9.3  (abort with ^G)

执行你的函数：

 1> my_mysql:do_mysql("Jeffsy", "2.0").
 ColumnNames: [<<"id">>,<<"name">>,<<"info">>]
 Rows: [[1,<<"7stud">>,<<"abc">>],
        [2,<<"Beth">>,<<"xxx">>],
        [3,<<"Diane">>,<<"xyz">>],
        [4,<<"Kathy">>,<<"xyz">>],
        [5,<<"Kathy">>,<<"xyz">>],
        [6,<<"Dave">>,<<"efg">>],
        [7,<<"Tom">>,<<"zzz">>],
        [8,<<"David">>,<<"abc">>],
        [9,<<"Eloise">>,<<"abc">>],
        [10,<<"Jess">>,<<"xyz">>],
        [11,<<"Jeffsy">>,<<"2.0">>]]
 ok

Erlang 无法连接到 mysql/mariadb

Erlang failing to connect to mysql/mariadb

mysql

erlang

mariadb

erlang-shell