How to join product collection of magento 2 to a custom table?

Question

I have a custom table user_product_table with a field sku(this field join to product collection) and user. How can I join this table with product collection, so that I don't have to loop my custom collection to get product in each row.

My $userCollection:

 $userCollection = $this->_userProductFactory->create()
        ->getCollection()
        ->addFieldToFilter('user', 2);

My product Collection:

$productColelction = $this->_productCollectionFactory->create()
        ->addAttributeToSelect(array('name','image','short_description','sku'))

I would like to have final collection both my custom table fields and selected product attributes.

Answer 1

We can use the join like this:

            $joinConditions = 'u.sku = e.sku';

            $productColelction->getSelect()->join(
                ['u' => $productColelction->getTable('user_product_table')],
                $joinConditions,
                []
            );

Multi conditions:

        $joinConditions[] = "u.sku = e.sku";

        $joinConditions[] = "e.type_id= 'simple' ";

        $joinConditions = implode(
            ' AND ', $joinConditions
        );