The @PrimaryKey annotation will mark a field as a primary key inside Realm. Only one field in a
RealmObject class can have this annotation, and the field should uniquely identify the object.
Trying to insert an object with an existing primary key will result in an
Primary keys also count as having the
It is allowed to apply this annotation on the following primitive types: byte, short, int, and long.
String, Byte, Short, Integer, and Long are also allowed, and further permitted to have
as a primary key value.