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枚举类型规定了取值的数量和内容，这对于需要限定取值的属性非常有帮助。比如性别有三种，男、女、未知，是否打印有两种，是，否。
package com.gxz.entities;
public enum Color {
RED,
GREEN,
BLUE
}
CREATE TABLE MyClothes (
MyClothesId BIGINT UNSIGNED PRIMARY KEY AUTO_INCREMENT,
Brand VARCHAR(255) NOT NULL,
Colour ENUM('RED','GREEN','BLUE'),
INDEX MyClothesBrand(Brand)
) ENGINE = InnoDB;DBMS使用MySQL，字段Colour是枚举类型，只能取值‘RED‘,‘GREEN‘,‘BLUE‘，若是插入其他值，报出异常。Operation failed: There was an error while applying the SQL script to the database.
Executing:
INSERT INTO `entitymappings`.`myclothes` (`MyClothesId`, `Brand`, `Colour`) VALUES ('1', '佐丹奴', 'BLANK');
ERROR 1265: 1265: Data truncated for column 'Colour' at row 1
SQL Statement:
INSERT INTO `entitymappings`.`myclothes` (`MyClothesId`, `Brand`, `Colour`) VALUES ('1', '佐丹奴', 'BLANK')
package com.gxz.entities;
import javax.persistence.Column;
import javax.persistence.Entity;
import javax.persistence.GeneratedValue;
import javax.persistence.GenerationType;
import javax.persistence.Id;
import javax.persistence.Table;
@Entity
@Table(name="myclothes")
public class Clothes {
private long id;
private Colour colour;
private String brand;
@Id
@GeneratedValue(strategy = GenerationType.IDENTITY)
@Column(name = "MyClothesId")
public long getId() {
return id;
}
public void setId(long id) {
this.id = id;
}
public Colour getColour() {
return colour;
}
public void setColour(Colour colour) {
this.colour = colour;
}
public String getBrand() {
return brand;
}
public void setBrand(String brand) {
this.brand = brand;
}
}
Clothes clothes = new Clothes();
clothes.setBrand("佐丹奴");
clothes.setColour(Colour.RED);
manager.persist(clothes);此时，报出异常。javax.persistence.PersistenceException: org.hibernate.exception.GenericJDBCException: could not execute statement Caused by: org.hibernate.exception.GenericJDBCException: could not execute statement Caused by: java.sql.SQLException: Data truncated for column 'Colour' at row 1默认情况，JPA实现者使用整数顺序值持久化枚举类型。枚举类型Colour定义取值的顺序是RED、GREEN、BLUE，因此，当这三个取值持久化到数据库表时，取值分别是0、1、2。然而，MySQL数据库表字段Colour是个枚举ENUM类型，只允许存放数值RED、GREEN、BLUE。所以持久化时，就会报出异常。为了印证以上的阐述，修改数据库表，让字段Colour的类型修改为varchar(1)，此时，该字段可以存放数值1、2、3。
CREATE TABLE MyClothes (
MyClothesId BIGINT UNSIGNED PRIMARY KEY AUTO_INCREMENT,
Brand VARCHAR(255) NOT NULL,
Colour VARCHAR(1) NOT NULL,
INDEX MyClothesBrand(Brand)
) ENGINE = InnoDB;执行持久化。Clothes clothes = new Clothes();
clothes.setBrand("佐丹奴");
clothes.setColour(Colour.RED);
manager.persist(clothes);
Clothes clothes2 = new Clothes();
clothes2.setBrand("真维斯");
clothes2.setColour(Colour.GREEN);
manager.persist(clothes2);
Clothes clothes3 = new Clothes();
clothes3.setBrand("以纯");
clothes3.setColour(Colour.BLUE);
manager.persist(clothes3);查看数据库表myclothes，如下所述。
package com.gxz.entities;
public enum Colour {
BLUE,
GREEN,
RED
}清空数据库表myclothes，执行持久化，查看数据，如下所述。
首先，我们把数据库表MyClothes的字段Colour修改回枚举型，接着，使用注解@Enumerated定义实体类。
package com.gxz.entities;
import javax.persistence.Column;
import javax.persistence.Entity;
import javax.persistence.EnumType;
import javax.persistence.Enumerated;
import javax.persistence.GeneratedValue;
import javax.persistence.GenerationType;
import javax.persistence.Id;
import javax.persistence.Table;
@Entity
@Table(name="myclothes")
public class Clothes {
private long id;
private Colour colour;
private String brand;
@Id
@GeneratedValue(strategy = GenerationType.IDENTITY)
@Column(name = "MyClothesId")
public long getId() {
return id;
}
public void setId(long id) {
this.id = id;
}
@Enumerated(EnumType.STRING)
public Colour getColour() {
return colour;
}
public void setColour(Colour colour) {
this.colour = colour;
}
public String getBrand() {
return brand;
}
public void setBrand(String brand) {
this.brand = brand;
}
}
执行持久化，查询数据库表MyClothes，结果如下所述。
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原文地址：http://blog.csdn.net/seedshome/article/details/52313417
