• All entities must declare a primary key/identifier
• Primary keys should be of the following types: any Java primitive type, any primitive wrapper type; java.lang.String; java.util.Date; java.sql.Date
• Do not use floating-point types!

Primary Key Example

• A primary key may be generated by the persistence provider

Auto-Generated Key Example

• The persistence provider may use a table/sequence to generate keys

Table-Generated Key Example