We have a school work, and we make a website with yii2 framework.

What is the problem? We cant use migration, what is the best way; we must to use an oracle database. We made it, tables, etc, but we dont know, how to connect this oracle ,,server,, with yii2.

You should go through the docs for Yii2.

You have to add the configuration in the common/config/main.php or config/db.php, depending upon the version of Yii2 (Advanced or Basic), and under the components you have to add the database component settings which are same for all databases, the only thing that differs is the dsn string below are all supported strings, that might help you or others landing on this question.

`For Advanced App`

Add the following under components

'db' => [
           'class' => 'yii\db\Connection',
           //'dsn' => 'mysql:host=localhost;dbname=mydatabase', // MySQL, MariaDB
           //'dsn' => 'sqlite:/path/to/database/file', // SQLite
           //'dsn' => 'pgsql:host=localhost;port=5432;dbname=mydatabase', // PostgreSQL
           //'dsn' => 'cubrid:dbname=demodb;host=localhost;port=33000', // CUBRID
           //'dsn' => 'sqlsrv:Server=localhost;Database=mydatabase', // MS SQL Server, sqlsrv driver
           //'dsn' => 'dblib:host=localhost;dbname=mydatabase', // MS SQL Server, dblib driver
           //'dsn' => 'mssql:host=localhost;dbname=mydatabase', // MS SQL Server, mssql driver
           'dsn' => 'oci:dbname=//localhost:1521/mydatabase', // Oracle
          'username' => 'DB_USERNAME',
          'password' => 'DB_PASSWORD',
          'charset' => 'utf8',
]

`For Basic App`

Just note that if you are using basic-app for Yii2 you should copy below inside the db.php

<?php 
return [
    'class' => 'yii\db\Connection' ,
    'dsn' => 'oci:dbname=//localhost:1521/mydatabase', // Oracle
    'username' => 'DB_USERNAME',
    'password' => 'DB_PASSWORD',
    'charset' => 'utf8' ,
];

and make sure you have