CakePHP 3.x - SUM() on ManyToMany - mysql

Question

I am getting stuck on using SQL functions queries made in CakePHP 3 in combinations with associations.
The situation is as follows: I have three tables, a 'products' table, an 'orders' table and a join table called 'orders_products'.
In the index of OrdersController I would like to add the total price (= sum of relevant product prices) to the table of orders. In SQL this exactly can be done with the following query:
SELECT orders.id, SUM(products.price)
FROM orders
LEFT JOIN orders_products
ON orders.id = orders_products.order_id
LEFT JOIN products
ON orders_products.product_id = products.id
GROUP BY orders.id;
I figured to following controller code should do the trick:
$orders = $this->Orders->find('all')->contain(['Products']);
$orders
->select(['total_price' => $orders->func()->sum('Products.price')])
->group('Orders.id');
However, when the query object is executed, I get an error:
Error: SQLSTATE[42S22]: Column not found: 1054 Unknown column
'Products.price' in 'field list'
...Even though the association between orders and products is defined.
Calling only $orders = $this->Orders->find('all')->contain(['Products'])->all(); does return an array of orders with each order a number of products, the model has to be set up correctly. Any ideas what might be wrong? Thanks in advance!
From OrdersTable:
$this->belongsToMany('Products', [
'foreignKey' => 'order_id',
'targetForeignKey' => 'product_id',
'joinTable' => 'orders_products'
]);
And from ProductsTable:
$this->belongsToMany('Orders', [
'foreignKey' => 'product_id',
'targetForeignKey' => 'order_id',
'joinTable' => 'orders_products'
]);

Answer 1

One way to do it:
$orders = $this->Orders->find()
->select([
'order_id' =>'orders.id',
'price_sum' => 'SUM(products.price)'
])
->leftJoin('orders_products', 'orders.id = orders_products.order_id'),
->leftJoin('products', 'orders_products.product_id = products.id')
->group('orders.id');