Order of many-to-many relationship

I've come across the need for this in a scenario which is analogous to orders / products.

I've got an "order" which is linked to one or more "products". However the order (position) in which the products appear in the order is significant. Therefore I have a "position" field in the join table.

The requirement is:

• To map the order of the array to values of the "position" field in the join table upon save.
• To hydrate the array ordered by the position field when hydrating the object.