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Database basics

Note: This section is under development.

Yii has a database access layer built on top of PHP's PDO. It provides uniform API and solves some inconsistencies between different DBMS. By default Yii supports the following DBMS:

MySQL
MariaDB
SQLite
PostgreSQL
CUBRID: version 9.1.0 or higher.
Oracle
MSSQL: version 2012 or above is required if you want to use LIMIT/OFFSET.

Configuration

In order to start using database you need to configure database connection component first by adding db component to application configuration (for "basic" web application it's config/web.php) like the following:

return [
    // ...
    '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' => 'root',
            'password' => '',
            'charset' => 'utf8',
        ],
    ],
    // ...
];

There is a peculiarity when you want to work with the database through the ODBC layer. When using ODBC, connection DSN doesn't indicate uniquely what database type is being used. That's why you have to override driverName property of yii\db\Connection class to disambiguate that:

'db' => [
	'class' => 'yii\db\Connection',
	'driverName' => 'mysql',
	'dsn' => 'odbc:Driver={MySQL};Server=localhost;Database=test',
	'username' => 'root',
	'password' => '',
],

Please refer to the PHP manual for more details on the format of the DSN string.

After the connection component is configured you can access it using the following syntax:

$connection = \Yii::$app->db;

You can refer to yii\db\Connection for a list of properties you can configure. Also note that you can define more than one connection component and use both at the same time if needed:

$primaryConnection = \Yii::$app->db;
$secondaryConnection = \Yii::$app->secondDb;

If you don't want to define the connection as an application component you can instantiate it directly:

$connection = new \yii\db\Connection([
    'dsn' => $dsn,
     'username' => $username,
     'password' => $password,
]);
$connection->open();

Tip: if you need to execute additional SQL queries right after establishing a connection you can add the following to your application configuration file:

return [
    // ...
    'components' => [
        // ...
        'db' => [
            'class' => 'yii\db\Connection',
            // ...
            'on afterOpen' => function($event) {
                $event->sender->createCommand("SET time_zone = 'UTC'")->execute();
            }
        ],
    ],
    // ...
];

Basic SQL queries

Once you have a connection instance you can execute SQL queries using yii\db\Command.

SELECT

When query returns a set of rows:

$command = $connection->createCommand('SELECT * FROM post');
$posts = $command->queryAll();

When only a single row is returned:

$command = $connection->createCommand('SELECT * FROM post WHERE id=1');
$post = $command->queryOne();

When there are multiple values from the same column:

$command = $connection->createCommand('SELECT title FROM post');
$titles = $command->queryColumn();

When there's a scalar value:

$command = $connection->createCommand('SELECT COUNT(*) FROM post');
$postCount = $command->queryScalar();

UPDATE, INSERT, DELETE etc.

If SQL executed doesn't return any data you can use command's execute method:

$command = $connection->createCommand('UPDATE post SET status=1 WHERE id=1');
$command->execute();

Alternatively the following syntax that takes care of proper table and column names quoting is possible:

// INSERT
$connection->createCommand()->insert('user', [
    'name' => 'Sam',
    'age' => 30,
])->execute();

// INSERT multiple rows at once
$connection->createCommand()->batchInsert('user', ['name', 'age'], [
    ['Tom', 30],
    ['Jane', 20],
    ['Linda', 25],
])->execute();

// UPDATE
$connection->createCommand()->update('user', ['status' => 1], 'age > 30')->execute();

// DELETE
$connection->createCommand()->delete('user', 'status = 0')->execute();

Quoting table and column names

Most of the time you would use the following syntax for quoting table and column names:

$sql = "SELECT COUNT([[$column]]) FROM {{table}}";
$rowCount = $connection->createCommand($sql)->queryScalar();

In the code above [[X]] will be converted to properly quoted column name while {{Y}} will be converted to properly quoted table name.

For table names there's a special variant {{%Y}} that allows you to automatically appending table prefix if it is set:

$sql = "SELECT COUNT([[$column]]) FROM {{%table}}";
$rowCount = $connection->createCommand($sql)->queryScalar();

The code above will result in selecting from tbl_table if you have table prefix configured like the following in your config file:

return [
    // ...
    'components' => [
        // ...
        'db' => [
            // ...
            'tablePrefix' => 'tbl_',
        ],
    ],
];

The alternative is to quote table and column names manually using yii\db\Connection::quoteTableName() and yii\db\Connection::quoteColumnName():

$column = $connection->quoteColumnName($column);
$table = $connection->quoteTableName($table);
$sql = "SELECT COUNT($column) FROM $table";
$rowCount = $connection->createCommand($sql)->queryScalar();

Prepared statements

In order to securely pass query parameters you can use prepared statements:

$command = $connection->createCommand('SELECT * FROM post WHERE id=:id');
$command->bindValue(':id', $_GET['id']);
$post = $command->query();

Another usage is performing a query multiple times while preparing it only once:

$command = $connection->createCommand('DELETE FROM post WHERE id=:id');
$command->bindParam(':id', $id);

$id = 1;
$command->execute();

$id = 2;
$command->execute();

Transactions

You can perform transactional SQL queries like the following:

$transaction = $connection->beginTransaction();
try {
    $connection->createCommand($sql1)->execute();
     $connection->createCommand($sql2)->execute();
    // ... executing other SQL statements ...
    $transaction->commit();
} catch(Exception $e) {
    $transaction->rollBack();
}

You can also nest multiple transactions, if needed:

// outer transaction
$transaction1 = $connection->beginTransaction();
try {
    $connection->createCommand($sql1)->execute();

    // inner transaction
    $transaction2 = $connection->beginTransaction();
    try {
        $connection->createCommand($sql2)->execute();
        $transaction2->commit();
    } catch (Exception $e) {
        $transaction2->rollBack();
    }

    $transaction1->commit();
} catch (Exception $e) {
    $transaction1->rollBack();
}

Working with database schema

Getting schema information

You can get a yii\db\Schema instance like the following:

$schema = $connection->getSchema();

It contains a set of methods allowing you to retrieve various information about the database:

$tables = $schema->getTableNames();

For the full reference check yii\db\Schema.

Modifying schema

Aside from basic SQL queries yii\db\Command contains a set of methods allowing to modify database schema:

createTable, renameTable, dropTable, truncateTable
addColumn, renameColumn, dropColumn, alterColumn
addPrimaryKey, dropPrimaryKey
addForeignKey, dropForeignKey
createIndex, dropIndex

These can be used as follows:

// CREATE TABLE
$connection->createCommand()->createTable('post', [
    'id' => 'pk',
    'title' => 'string',
    'text' => 'text',
]);

For the full reference check yii\db\Command.

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