The engine works with MySQL/MariaDB through the thin façade DB (a wrapper over mysqli). The class is App\Common\Db\DB, but the short global alias DB is used everywhere. The query result is returned as object DB_Result.

$doc = DB::query('SELECT * FROM ' . $t . ' WHERE Id = %i', 42)->getAssoc();

Section map

Page	What about
Table names (resolvers)	How to correctly get the table name (`ContentTables`, `SystemTables`, ...) instead of the hardcode.
Placeholders	Full analysis of `%i %s %ss %li %hc …` with examples of each.
Queries	`DB::query()` and variants (`queryAssoc`, `queryOneColumn` ...), debugging.
Read result (DB_Result)	`getAll / getAssoc / getValue / getOne …`, semantics and pitfalls.
CRUD helpers	`Insert / Update / Delete / Replace / insertUpdate`, `insertId`, `affectedRows`.
Transactions	`startTransaction / commit / rollback`.
Query cache	`setTtl / setCache / setTags / clearTags`.
Safety and Shielding	Injection protection, `escape / quote / safe`.

Connection

The connection is raised once at system/bootstrap.php (DB::getInstance($config)), therefore, there is no need to initialize anything in controllers/models - right away DB::query(...).

DB::connection('default');   // именованное соединение
DB::setPrefix('marketplace'); // префикс (обычно из настроек)
DB::mysqli();                 // «сырой» mysqli при необходимости
DB::version();                // версия сервера
DB::getDatabase();            // имя текущей БД

Quick start

use App\Content\ContentTables;
$t = ContentTables::table('documents');   // for example, 'ave_documents'

// список (массив ассоц. строк; на пустой выборке — false)
$items = DB::query('SELECT * FROM ' . $t . ' WHERE rubric_id = %i ORDER BY Id DESC', 5)->getAll() ?: array();

// одна строка
$doc = DB::query('SELECT * FROM ' . $t . ' WHERE Id = %i', 42)->getAssoc();

// один скаляр
$count = (int) DB::query('SELECT COUNT(*) FROM ' . $t)->getValue();

// вставка
DB::Insert($t, array('document_title' => 'Тест', 'rubric_id' => 5));
$id = (int) DB::insertId();

// обновление / удаление
DB::Update($t, array('document_title' => 'Новый'), 'Id = %i', $id);
DB::Delete($t, 'Id = %i', $id);

Three rules

Table name - via resolver (ContentTables::table('documents')), not a string. → tables.md
Values - only through placeholders (%i, %s, ...), never merge user input in SQL. → placeholders.md, security.md
getAll() on an empty sample returns false, and not [] - write ?: array(). → results.md