Product Reference Field (Legacy Version)
Product Reference Fields allow you to reference one or more to products in your store.
This is a legacy field type. This field type should only be used inside Field Collections or Widgets.
See also: Product Reference Field
Content Entry Form
The content entry form uses a dynamic search to allow content to be entered based on the name of the product. For technical reasons, once a product is selected, the app must save the data as the handle to the product so that it may be used in code.
The maximum number of products that can be referenced is limited to 20, due to technical limitations within Shopify.
The all_products Shopify Variable
The Related Products field type is made possible by the all_products variable in Shopify. Please refer to the additional links below for details.
Shopify: How to Use all_products in a Shopify Theme