I´m diving in custom resource´s creation, specially in defining links. I have always used "Define specific keys to make the join" when defining joins: i select one field from every resource involved in the link and thats how resources are joined.
I see that there is also another option available: "Use the primary keys to make the join".
I would like to undertand how could i use this option to join resources. If i set this option, which field does ACS use from the source resource to link to the target resource ?(i guess that it uses target resource´s primary key)
Yes, it uses both the resources primary keys to make join. For example if you have "store review" custom resource which contains store code as primary key and another custom resource "store details" custom resource which contains store code as primary key again then if you create link with option "Use the primary keys to make join" will enable link between store review and store details resource using store code as key.