class DbtngExampleRepository

class DbtngExampleRepository {
    use MessengerTrait;
    use StringTranslationTrait;
    
    /**
     * The database connection.
     *
     * @var \Drupal\Core\Database\Connection
     */
    protected $connection;
    
    /**
     * Construct a repository object.
     *
     * @param \Drupal\Core\Database\Connection $connection
     *   The database connection.
     * @param \Drupal\Core\StringTranslation\TranslationInterface $translation
     *   The translation service.
     * @param \Drupal\Core\Messenger\MessengerInterface $messenger
     *   The messenger service.
     */
    public function __construct(Connection $connection, TranslationInterface $translation, MessengerInterface $messenger) {
        $this->connection = $connection;
        $this->setStringTranslation($translation);
        $this->setMessenger($messenger);
    }
    
    /**
     * Save an entry in the database.
     *
     * Exception handling is shown in this example. It could be simplified
     * without the try/catch blocks, but since an insert will throw an exception
     * and terminate your application if the exception is not handled, it is best
     * to employ try/catch.
     *
     * @param array $entry
     *   An array containing all the fields of the database record.
     *
     * @return int
     *   The number of updated rows.
     *
     * @throws \Exception
     *   When the database insert fails.
     */
    public function insert(array $entry) {
        try {
            $return_value = $this->connection
                ->insert('dbtng_example')
                ->fields($entry)
                ->execute();
        } catch (\Exception $e) {
            $this->messenger()
                ->addMessage($this->t('Insert failed. Message = %message', [
                '%message' => $e->getMessage(),
            ]), 'error');
        }
        return $return_value ?? NULL;
    }
    
    /**
     * Update an entry in the database.
     *
     * @param array $entry
     *   An array containing all the fields of the item to be updated.
     *
     * @return int
     *   The number of updated rows.
     */
    public function update(array $entry) {
        try {
            // Connection->update()...->execute() returns the number of rows updated.
            $count = $this->connection
                ->update('dbtng_example')
                ->fields($entry)
                ->condition('pid', $entry['pid'])
                ->execute();
        } catch (\Exception $e) {
            $this->messenger()
                ->addMessage($this->t('Update failed. Message = %message, query= %query', [
                '%message' => $e->getMessage(),
                '%query' => $e->query_string,
            ]), 'error');
        }
        return $count ?? 0;
    }
    
    /**
     * Delete an entry from the database.
     *
     * @param array $entry
     *   An array containing at least the person identifier 'pid' element of the
     *   entry to delete.
     *
     * @see Drupal\Core\Database\Connection::delete()
     */
    public function delete(array $entry) {
        $this->connection
            ->delete('dbtng_example')
            ->condition('pid', $entry['pid'])
            ->execute();
    }
    
    /**
     * Read from the database using a filter array.
     *
     * The standard function to perform reads for static queries is
     * Connection::query().
     *
     * Connection::query() uses an SQL query with placeholders and arguments as
     * parameters.
     *
     * Drupal DBTNG provides an abstracted interface that will work with a wide
     * variety of database engines.
     *
     * The following is a query which uses a string literal SQL query. The
     * placeholders will be substituted with the values in the array. Placeholders
     * are marked with a colon ':'. Table names are marked with braces, so that
     * Drupal's' multisite feature can add prefixes as needed.
     *
     * @code
     *   // SELECT * FROM {dbtng_example} WHERE uid = 0 AND name = 'John'
     *   \Drupal::database()->query(
     *     "SELECT * FROM {dbtng_example} WHERE uid = :uid and name = :name",
     *     [':uid' => 0, ':name' => 'John']
     *   )->execute();
     * @endcode
     *
     * For more dynamic queries, Drupal provides Connection::select() API method,
     * so there are several ways to perform the same SQL query. See the
     * @link http://drupal.org/node/310075 handbook page on dynamic queries. @endlink
     * @code
     *   // SELECT * FROM {dbtng_example} WHERE uid = 0 AND name = 'John'
     *   \Drupal::database()->select('dbtng_example')
     *     ->fields('dbtng_example')
     *     ->condition('uid', 0)
     *     ->condition('name', 'John')
     *     ->execute();
     * @endcode
     *
     * Here is select() with named placeholders:
     * @code
     *   // SELECT * FROM {dbtng_example} WHERE uid = 0 AND name = 'John'
     *   $arguments = array(':name' => 'John', ':uid' => 0);
     *   \Drupal::database()->select('dbtng_example')
     *     ->fields('dbtng_example')
     *     ->where('uid = :uid AND name = :name', $arguments)
     *     ->execute();
     * @endcode
     *
     * Conditions are stacked and evaluated as AND and OR depending on the type of
     * query. For more information, read the conditional queries handbook page at:
     * http://drupal.org/node/310086
     *
     * The condition argument is an 'equal' evaluation by default, but this can be
     * altered:
     * @code
     *   // SELECT * FROM {dbtng_example} WHERE age > 18
     *   \Drupal::database()->select('dbtng_example')
     *     ->fields('dbtng_example')
     *     ->condition('age', 18, '>')
     *     ->execute();
     * @endcode
     *
     * @param array $entry
     *   An array containing all the fields used to search the entries in the
     *   table.
     *
     * @return object
     *   An object containing the loaded entries if found.
     *
     * @see Drupal\Core\Database\Connection::select()
     */
    public function load(array $entry = []) {
        // Read all the fields from the dbtng_example table.
        $select = $this->connection
            ->select('dbtng_example')
            ->fields('dbtng_example');
        // Add each field and value as a condition to this query.
        foreach ($entry as $field => $value) {
            $select->condition($field, $value);
        }
        // Return the result in object format.
        return $select->execute()
            ->fetchAll();
    }
    
    /**
     * Load dbtng_example records joined with user records.
     *
     * DBTNG also helps processing queries that return several rows, providing the
     * found objects in the same query execution call.
     *
     * This function queries the database using a JOIN between users table and the
     * example entries, to provide the username that created the entry, and
     * creates a table with the results, processing each row.
     *
     * SELECT
     *  e.pid as pid, e.name as name, e.surname as surname, e.age as age
     *  u.name as username
     * FROM
     *  {dbtng_example} e
     * JOIN
     *  users u ON e.uid = u.uid
     * WHERE
     *  e.name = 'John' AND e.age > 18
     *
     * @see Drupal\Core\Database\Connection::select()
     * @see http://drupal.org/node/310075
     */
    public function advancedLoad() {
        // Get a select query for our dbtng_example table. We supply an alias of e
        // (for 'example').
        $select = $this->connection
            ->select('dbtng_example', 'e');
        // Join the users table, so we can get the entry creator's username.
        $select->join('users_field_data', 'u', 'e.uid = u.uid');
        // Select these specific fields for the output.
        $select->addField('e', 'pid');
        $select->addField('u', 'name', 'username');
        $select->addField('e', 'name');
        $select->addField('e', 'surname');
        $select->addField('e', 'age');
        // Filter only persons named "John".
        $select->condition('e.name', 'John');
        // Filter only persons older than 18 years.
        $select->condition('e.age', 18, '>');
        // Make sure we only get items 0-49, for scalability reasons.
        $select->range(0, 50);
        $entries = $select->execute()
            ->fetchAll(\PDO::FETCH_ASSOC);
        return $entries;
    }

}