One-to-many relationships

Object relationships are defined by the Linkable interface. All Para objects are linkable, meaning that they can be related to other Para objects.

Para supports one-to-many relationships between objects with the parentid field. It contains the id of the parent object. For example a user might be linked to their father like this:

+--------+
| Darth  |
| id: 5  |  Parent
+---+----+
    |
+---+---------+
| Luke        |
| id: 10      |  Child
| parentid: 5 |
+-------------+

This allows us to have a parent objects with many children which have the same parentid set. Now we can get all children for a given object by calling parent.getChildren(Class<P> clazz). This will return the list of objects that have a parentid equal to that object’s id. For example:

// assuming we have the parent object...
User luke = parent.getChildren(User.class).get(0);
User darth = dao.read(luke.getParentid());