首先需要添加ConnectionManager:

First you need to add the ConnectionManager:

use CakeDatasourceConnectionManager;

然后你需要像这样获得你的连接:

Then you need to get your connection like so:

// my_connection is defined in your database config
$conn = ConnectionManager::get('my_connection');

更多信息:http://book.cakephp.org/3.0/en/orm/database-basics.html#creating-connections-at-runtime

之后，您可以像这样运行自定义查询:

After that you can run a custom query like this:

$stmt = $conn->execute('UPDATE posts SET published = ? WHERE id = ?', [1, 2]);

更多信息:http://book.cakephp.org/3.0/en/orm/database-basics.html#executing-queries

然后您就可以像这样获取行了:

And then you are ready to fetch the row(s) like this:

// Read one row.
$row = $stmt->fetch('assoc');

// Read all rows.
$rows = $stmt->fetchAll('assoc');

// Read rows through iteration.
foreach ($rows as $row) {
    // Do work
}

更多信息:http://book.cakephp.org/3.0/en/orm/database-basics.html#executing-fetching-rows