WP_Query Woocommerce products that belong in distinct multiple categories only tax_query

Wow, so after hours of banging my head, this is how I was able to solve this -

$args = array(    'posts_per_page' => -1,    'tax_query' => array(        'relation' => 'AND',        array(            'taxonomy' => 'product_cat',            'field' => 'slug',            'terms' => 'category-slug1'        ),        array(            'taxonomy' => 'product_cat',            'field' => 'slug',            'terms' => 'category-slug2'        )    ),    'post_type' => 'product',    'orderby' => 'title',);$the_query = new WP_Query( $args );

This takes advantage of the tax_query argument, including the relation => 'AND' to make sure the product falls under BOTH categories.

Hope this helps someone in the future.

I was also not able to figure out how to pass an ID, rather than a slug (although I'm sure there's a way), but here's the function to retrieve the slug based on an ID:

$terms = get_term($YOURID, 'product_cat'); $theslug = $terms->slug; 

To query by category_ID this is what worked for me.

// First obtain term id://...$all_categories = get_categories( $args );$cat_ids = array();foreach ($all_categories as $cat) {     array_push($cat_ids, $cat->term_id);}//Now use ids from array:$args = array(    'posts_per_page' => -1,    'post_type' => 'product',    'tax_query'     => array(        array(            'taxonomy'  => 'product_cat',            'field'     => 'id',             'terms'     => $cat_ids        )    ));

From the WordPress codex on WP_Query for Category Parameters:

equivalent of OR

$args = array( 'product_cat' => 'category-slug1,category-slug2' ) );

equivalent of AND

$args = array( 'product_cat' => 'category-slug1+category-slug2' );

e.g.

$query = new WP_Query( $args );