DB_CONNECTION=mysql
DB_HOST=127.0.0.1
DB_PORT=3306
DB_DATABASE=database_name
DB_USERNAME=root
DB_PASSWORD=root

DB_HOST_TEST=127.0.0.1
DB_PORT_TEST=3306
DB_DATABASE_TEST=database_test
DB_USERNAME_TEST=root
DB_PASSWORD_TEST=root

// 默认连接mysql
'default' => env('DB_CONNECTION', 'mysql'),

'connections' => [

 'sqlite' => [
  'driver' => 'sqlite',
  'database' => database_path('database.sqlite'),
  'prefix' => '',
 ],

 'mysql' => [
  'driver' => 'mysql',
  'host' => env('DB_HOST', '127.0.0.1'),
  'port' => env('DB_PORT', '3306'),
  'database' => env('DB_DATABASE', 'database_name'),
  'username' => env('DB_USERNAME', 'root'),
  'password' => env('DB_PASSWORD', 'root'),
  'charset' => 'utf8',
  'collation' => 'utf8_unicode_ci',
  'prefix' => '',
  'strict' => false,
 ],

 'mysql_test' => [
  'driver' => 'mysql',
  'host' => env('DB_HOST_TEST', '127.0.0.1'),
  'port' => env('DB_PORT_TEST', '3306'),
  'database' => env('DB_DATABASE_TEST', 'database_test'),
  'username' => env('DB_USERNAME_TEST', 'root'),
  'password' => env('DB_PASSWORD_TEST', 'root'),
  'charset' => 'utf8',
  'collation' => 'utf8_unicode_ci',
  'prefix' => '',
  'strict' => false,
 ],

 ],

?php

namespace App\Model;

use Illuminate\Database\Eloquent\Model;

class Test extends Model
{
 // 数据库'database_test'中的test表
 public $table = 'test';
 public $timestamps = false;
 protected $connection = 'mysql_test';

}

?php

namespace App\Model;

use Illuminate\Database\Eloquent\Model;

class Test extends Model
{
 // 数据库'database'中的test表
 public $table = 'test';
 public $timestamps = false;
 // 以下代码可有可不、默认连接mysql
 protected $connection = 'mysql';

}


a、这个model将采用默认的'mysql'连接
class UserModel extends Model
{
 // 数据库'database'中的users表
 protected $table = "users";
}

b、 

// 以下是调用方法
Test::get();
Test::where('id',1)->first();

// 连接mysql_test库
DB::connection('mysql_test')->table('test')->where('id',1)->first();
// 连接mysql库
DB::connection('mysq')->table('test')->where('id',1)->first();
// 连接mysql库
DB::table('test')->where('id',1)->first();