Gem mysql2适配器未安装

当我尝试安装

mysql2

适配器gem时，出现以下错误：

gem install mysql2 -v 0.3.21
Building native extensions.  This could take a while...
ERROR:  Error installing mysql2:
    ERROR: Failed to build gem native extension.

    /Users/jwan/.rbenv/versions/2.1.2/bin/ruby extconf.rb
checking for ruby/thread.h... yes
checking for rb_thread_call_without_gvl() in ruby/thread.h... yes
checking for rb_thread_blocking_region()... yes
checking for rb_wait_for_single_fd()... yes
checking for rb_hash_dup()... yes
checking for rb_intern3()... yes
-----
Using mysql_config at /usr/local/bin/mysql_config
-----
checking for mysql.h... yes
checking for errmsg.h... yes
checking for mysqld_error.h... yes
-----
Setting rpath to /usr/local/Cellar/mysql/8.0.12/lib
-----
creating Makefile

make "DESTDIR=" clean

make "DESTDIR="
compiling infile.c
compiling client.c
client.c:439:3: error: use of undeclared identifier 'my_bool'
  my_bool res = mysql_read_query_result(client);
  ^
client.c:441:19: error: use of undeclared identifier 'res'
  return (void *)(res == 0 ? Qtrue : Qfalse);
                  ^
client.c:762:3: error: use of undeclared identifier 'my_bool'
  my_bool boolval;
  ^
client.c:793:7: error: use of undeclared identifier 'boolval'
      boolval = (value == Qfalse ? 0 : 1);
      ^
client.c:794:17: error: use of undeclared identifier 'boolval'
      retval = &boolval;
                ^
client.c:797:10: error: use of undeclared identifier 'MYSQL_SECURE_AUTH'; did you mean 'MYSQL_DEFAULT_AUTH'?
    case MYSQL_SECURE_AUTH:
         ^~~~~~~~~~~~~~~~~
         MYSQL_DEFAULT_AUTH
/usr/local/Cellar/mysql/8.0.12/include/mysql/mysql.h:188:3: note: 'MYSQL_DEFAULT_AUTH' declared here
  MYSQL_DEFAULT_AUTH,
  ^
client.c:798:7: error: use of undeclared identifier 'boolval'
      boolval = (value == Qfalse ? 0 : 1);
      ^
client.c:799:17: error: use of undeclared identifier 'boolval'
      retval = &boolval;
                ^
client.c:830:38: error: use of undeclared identifier 'boolval'
        wrapper->reconnect_enabled = boolval;
                                     ^
client.c:1185:38: error: use of undeclared identifier 'MYSQL_SECURE_AUTH'; did you mean 'MYSQL_DEFAULT_AUTH'?
  return _mysql_client_options(self, MYSQL_SECURE_AUTH, value);
                                     ^~~~~~~~~~~~~~~~~
                                     MYSQL_DEFAULT_AUTH
/usr/local/Cellar/mysql/8.0.12/include/mysql/mysql.h:188:3: note: 'MYSQL_DEFAULT_AUTH' declared here
  MYSQL_DEFAULT_AUTH,
  ^
10 errors generated.
make: *** [client.o] Error 1

make failed, exit code 2

Gem files will remain installed in /Users/jwan/.rbenv/versions/2.1.2/lib/ruby/gems/2.1.0/gems/mysql2-0.3.21 for inspection.

这意味着什么？发生了什么

此行的作用是：

将rpath设置为/usr/local/ceral/mysql/8.0.12/lib

---

我可以试着把它指向另一个版本的mysql吗？

因为你的rails版本使用的是一个不可映射的mysql2 gem版本，你必须使gem文件中的所有gem版本正确匹配一个很好的方法是使用google rubygems（gem名称）版本，查看它的运行时依赖关系和发布日期发布日期可以与rails版本和其他gem的发布日期进行比较，这取决于您何时是新版本，这可能需要一点时间