Database: Getting Started

#Introduction

Connecting to databases and running queries is a simple process, supported by using either raw SQL, the query builder or active record models. Managing database tables and populating seed data is handled by the migration and seeder process.

Raw SQL and using the query builder will perform faster and should be used for simple tasks. Active Record is an approach used by the popular framework, Ruby On Rails. It allows an easy interface for performing repetitive tasks like creating, reading, updating and deleting database records. You can learn more about the active record pattern on Wikipedia.

#Configuration

The database configuration for your application is located in the config/database.php file. In this file you may define all of your database connections, as well as specify which connection should be used by default. Examples for all of the supported database systems are provided in this file.

#Read / write connections

Sometimes you may wish to use one database connection for SELECT statements, and another for INSERT, UPDATE, and DELETE statements. It is easy to specify which connection is used whether you are using raw queries, the query builder or a model.

To see how read / write connections should be configured, let's look at this example:

'mysql' => [
    'read' => [
        'host' => '192.168.1.1',
    ],
    'write' => [
        'host' => '196.168.1.2'
    ],
    'driver'    => 'mysql',
    'database'  => 'database',
    'username'  => 'root',
    'password'  => '',
    'charset'   => 'utf8',
    'collation' => 'utf8_unicode_ci',
    'prefix'    => '',
],

Note that two keys have been added to the configuration array: read and write. Both of these keys have array values containing a single key: host. The rest of the database options for the read and write connections will be merged from the main mysql array.

We only need to place items in the read and write arrays if we wish to override the values in the main array. So, in this case, 192.168.1.1 will be used as the "read" connection, while 192.168.1.2 will be used as the "write" connection. The database credentials, prefix, character set, and all other options in the main mysql array will be shared across both connections.

#Running raw SQL queries

Once you have configured your database connection, you may run queries using the Db facade. The Db facade provides methods for each type of query: select, update, insert, delete, and statement.

#Running a select query

To run a basic query, we can use the select method on the Db facade:

$users = Db::select('select * from users where active = ?', [1]);

The first argument passed to the select method is the raw SQL query, while the second argument is any parameter bindings that need to be bound to the query. Typically, these are the values of the where clause constraints. Parameter binding provides protection against SQL injection.

The select method will always return an array of results. Each result within the array will be a PHP stdClass object, allowing you to access the values of the results:

foreach ($users as $user) {
    echo $user->name;
}

#Using named bindings

Instead of using ? to represent your parameter bindings, you may execute a query using named bindings:

$results = Db::select('select * from users where id = :id', ['id' => 1]);

#Running an insert statement

To execute an insert statement, you may use the insert method on the Db facade. Like select, this method takes the raw SQL query as its first argument and bindings as the second argument:

Db::insert('insert into users (id, name) values (?, ?)', [1, 'Joe']);

#Running an update statement

The update method should be used to update existing records in the database. The number of rows affected by the statement will be returned by the method:

$affected = Db::update('update users set votes = 100 where name = ?', ['John']);

#Running a delete statement

The delete method should be used to delete records from the database. Like update, the number of rows deleted will be returned:

$deleted = Db::delete('delete from users');

#Running a general statement

Some database statements should not return any value. For these types of operations, you may use the statement method on the Db facade:

Db::statement('drop table users');

#Multiple database connections

When using multiple connections, you may access each connection via the connection method on the Db facade. The name passed to the connection method should correspond to one of the connections listed in your config/database.php configuration file:

$users = Db::connection('foo')->select(...);

You may also access the raw, underlying PDO instance using the getPdo method on a connection instance:

$pdo = Db::connection()->getPdo();

#Database transactions

To run a set of operations within a database transaction, you may use the transaction method on the Db facade. If an exception is thrown within the transaction Closure, the transaction will automatically be rolled back. If the Closure executes successfully, the transaction will automatically be committed. You don't need to worry about manually rolling back or committing while using the transaction method:

Db::transaction(function () {
    Db::table('users')->update(['votes' => 1]);

    Db::table('posts')->delete();
});

#Manually using transactions

If you would like to begin a transaction manually and have complete control over rollbacks and commits, you may use the beginTransaction method on the Db facade:

Db::beginTransaction();

You can rollback the transaction via the rollBack method:

Db::rollBack();

Lastly, you can commit a transaction via the commit method:

Db::commit();

NOTE: Using the Db facade's transaction methods also controls transactions for the query builder and model queries.

#Database events

If you would like to receive each SQL query executed by your application, you may use the listen method. This method is useful for logging queries or debugging.

Db::listen(function ($sql, $bindings, $time) {
    //
});

Just like event registration, you may register your query listener in the boot method of a Plugin registration file. Alternatively, plugins can supply a file named init.php in the plugin directory that you can use to place this logic.

#Query logging

When query logging is enabled, a log is kept in memory of all queries that have been run for the current request. Call the enableQueryLog method to enable this feature.

Db::connection()->enableQueryLog();

To get an array of the executed queries, you may use the getQueryLog method:

$queries = Db::getQueryLog();

However, in some cases, such as when inserting a large number of rows, this can cause the application to use excess memory. To disable the log, you may use the disableQueryLog method:

Db::connection()->disableQueryLog();

NOTE: For quicker debugging it may be more useful to call the trace_sql helper function instead.