Relational Mapping: The Future of Relational Databases

In relational schemas if we want to have a table that refers like a row in this table needs it's called a foreign key. The constraint in the database make sure that you that the value you put in those columns actually exist in the remote. OrM ORMs have this concept of either making a one to many or many to many or a many to one relationship which models in I was joined in terms what that looks like in terms of collections.