Enum field in JPA Entity

Question

I feel a little dumb asking this but I can't find any simple answer to the question.

Take this simple entity as example:

@Entity @Table( name="clienti" ) public class Cliente implements Serializable {      private static final long serialVersionUID = 1L;      @Id     @GeneratedValue(strategy = GenerationType.IDENTITY)     @Column(name = "id")     private Long id;      private String nome;      private String cognome;  //... } 

It represents a person, so I want to add a "gender" property.

It will be "male" or "female". So what?

I can use a String, and keep in mind that "m" stands for male and "f" for female.

Or I can use a boolean "isMale", true or false.

However, I don't think in either case Hibernate purists would be happy :)

Googling a little bit I found that the best practice is using an enum.

I am a little confused on how to use it. Can you help me with an example?

Answer 1

You can map your enum to a String or to an ordinal number. Mapping to String is the more portable approach as the mapping will survive changing the enumeration order.

Using your example:

@Entity @Table( name="clienti" ) public class Cliente implements Serializable {  ...     @Enumerated(EnumType.STRING)     private Gender gender; ... } 

The string mapping will use the simple name of the enumeration type, so you would have two possible values in the DB - 'Male' and 'Female'

public enum Gender { MALE, FEMALE } 

The persistence provider takes care of the mapping, so in your code, you can continue using the Gender enum and not worry about Strings or ordinals.

Answer 2

public enum Gender{      MALE, FEMALE  }    @Entity @Table( name="clienti" ) public class Cliente implements Serializable { ...  // **1 case** - If database column type is number (integer)  // (some time for better search performance)  -> we should use  // EnumType.ORDINAL as @O.Badr noticed. e.g. inserted number will // index of constant starting from 0... in our example for MALE - 0, FEMALE - 1. // **Possible issue (advice)**: you have to add the new values at the end of // your enum, in order to keep the ordinal correct for future values.  @Enumerated(EnumType.ORDINAL)     private Gender gender;   // **2 case** - If database column type is character (varchar)  // and you want to save it as String constant then ->  @Enumerated(EnumType.STRING)     private Gender gender;  ... }  // in all case on code level you will interact with defined  // type of Enum constant but in Database level 

first case (EnumType.ORDINAL)

╔════╦══════════════╦════════╗ ║ ID ║    NAME      ║ GENDER ║ ╠════╬══════════════╬════════╣ ║  1 ║ Jeff Atwood  ║    0   ║ ║  2 ║ Geoff Dalgas ║    0   ║ ║  3 ║Jarrod Jesica ║    1   ║ ║  4 ║ Joel Lucy    ║    1   ║ ╚════╩══════════════╩════════╝ 

second case (EnumType.STRING)

╔════╦══════════════╦════════╗ ║ ID ║    NAME      ║ GENDER ║ ╠════╬══════════════╬════════╣ ║  1 ║ Jeff Atwood  ║  MALE  ║ ║  2 ║ Geoff Dalgas ║  MALE  ║ ║  3 ║Jarrod Jesica ║ FEMALE ║ ║  4 ║ Joel Lucy    ║ FEMALE ║ ╚════╩══════════════╩════════╝