Как выполнить операцию sum (sum a field) в ассоциированной таблице модели с помощью cakephp 3.2

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I want to sum up a field in cakephp 3.2. But the field is present in hasOne model association.



I want to do it in the bind query .

I have a order table and i am doing model bind with collection table .

Here i want to sum up all the due_amount in collections table

 

I have tried but its not working.

Please check my code,Is there any thing wrong with it.?

 $this->Orders->hasOne('Collections', [
                'className' => 'Collections',
                'foreignKey' => 'order_id',
                'strategy' => 'select',
                'conditions' => function (\Cake\Database\Expression\QueryExpression $exp, \Cake\ORM\Query $query) {
                    $query->order(['Collections.id' => 'ASC']);
                    return [];
                }
                    ]);
            $get_total_sales = $this->Orders->find('all')->where($condition)->select(['id', 'region_id', 'net_total'])->contain(['Collections' => ['queryBuilder' => function ($q) {
                                return $q->select(['id', 'order_id', 'total_sale_amount', 'due_amount']);
                            }]])->order(['Orders.due_date DESC']);


$res2 = $get_total_sales->select(['total_due' =>$get_total_sales->func()->sum('collection.due_amount')])->first(); 

 echo  $due = $res2->total_due;//its showing column not find error.
Is it working in order table instead of collections table?
How can i do it for collection table using the $get_total_sales listing results?



Below some out put 

[
    {
        "id": 40,
        "region_id": 2,
        "net_total": 2899.12,
        "collection": {
            "id": 182,
            "order_id": 40,
            "total_sale_amount": 2899.12,
            "due_amount": 1990
        },

    },
    {
        "id": 38,
        "region_id": 2,
        "net_total": 110,
        "collection": {
            "id": 181,
            "order_id": 38,
            "total_sale_amount": 110,
            "due_amount": 10
        },

    },
    {
        "id": 39,
        "region_id": 2,
        "net_total": 16670,
        "collection": {
            "id": 190,
            "order_id": 39,
            "total_sale_amount": 16670,
            "due_amount": 16630.99
        },

    },

Here i want to sum up all the due_amount in collections table

Thank you

Что я уже пробовал:

$res2 = $get_total_sales-и GT;выберите(['total_due' =&ГТ;$get_total_sales-&ГТ;кнопку func()-&ГТ;взыскание сумм ('.due_amount')])-&ГТ;первый();

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