CakePHP - add custom SQL to a Query object - orm

Question

I'm using CakePHP 3.5.13 to build an application which has 4 separate databases.
The main database (Datasource default in config/app.php) for the application has been baked. It was a legacy database, and the naming conventions are not written according to the way CakePHP specifies. Nonetheless it works, after going through the Models and editing things.
In a controller I have the following:
$substances = TableRegistry::get('Substances');
$query = $substances->find()->limit(250)->offset(0);
$query->select(['id', 'app_id', 'name']);
$query->contain([
'Cas' => [
'sort' => ['Cas.id' => 'ASC']
]
]);
$query->contain([
'Ecs' => [
'sort' => ['Ecs.id' => 'ASC']
]
]);
If I var_dump($query) I get an SQL string as follows:
SELECT Substances.id AS `Substances__id`,
Substances.app_id AS `Substances__app_id`,
Substances.name AS `Substances__name`
FROM substances Substances LIMIT 250 OFFSET 0
I need to modify this so the query contains an INNER JOIN to a table which is stored in one of the other databases (Datasource sdb5_tmpdata in config/app.php). The SQL I need is as follows:
SELECT Substances.id AS `Substances__id`,
Substances.app_id AS `Substances__app_id`,
Substances.name AS `Substances__name`,
Substances.date AS `Substances__date`
FROM substances Substances
INNER JOIN `sdb5_tmpdata`.`searching_1745` AS tf
ON tf.id = Substances.id LIMIT 250 OFFSET 0;
The difference between the above query and original is the following SQL:
INNER JOIN `sdb5_tmpdata`.`searching_1745` AS tf
ON tf.id = Substances.id
I don't have a corresponding Model for the table 'searching_1745' because these tables are dynamically created (and later dropped) on a database which holds "temporary" user data.
Is it possible to modify the query object, $query, such that I can introduce the custom SQL that does the inner join?
I have tried $query = $query->newExpr()->add('INNER JOIN 'sdb5_tmpdata'.'searching_1745' AS tf ON tf.id = Substances.id'); but it doesn't work.

Answer 1

the query builder let you build the query as you like it. It does not matter if you don't have a Table Object for that table
$query->join([
'tf ' => [
'table' => 'sdb5_tmpdata.searching_1745',
'type' => 'INNER',
'conditions' => 'tf.id = Substances.id',
]);
see here

Answer 2

I don't know if you can modify the query object, but tou can always write your own custom queries:
use Cake\Datasource\ConnectionManager;
$conn = ConnectionManager::get('default');
$query = $conn->query('query goes here');
for more info, read: https://book.cakephp.org/3.0/en/orm/database-basics.html#executing-queries