hibernate one to one Annotation

1. 外键单向(unidirectional with foreign key )

create table USERS(
	PK_USER_ID	INT IDENTITY NOT NULL,
	USER_ID		VARCHAR(50)	NOT NULL,
	FK_GROUP_ID	INT	NOT NULL

)

create table USER_GROUP(
	PK_GROUP_ID	INT IDENTITY NOT NULL,
	GROUP_NAME		VARCHAR(50)	NOT NULL,
	LAST_UPDATED_BY	VARCHAR(50)	NOT NULL,
	LAST_UPDATED_DATE DATETIME NOT NULL
)

@Entity
@Table(name = "USERS")
public class User {
	private int pkUserId;
	private String userId;
	private Group group;

	public User(){}

	@Id
	@GeneratedValue(strategy = IDENTITY)
	@Column(name = "PK_USER_ID", unique = true, nullable = false)
	public int getPkUserId() {
		return pkUserId;
	}

	public void setPkUserId(int pkUserId) {
		this.pkUserId = pkUserId;
	}

	@Column(name = "USER_ID", unique = true, nullable = false)
	public String getUserId() {
		return userId;
	}

	public void setUserId(String userId) {
		this.userId = userId;
	}

	@OneToOne(fetch = FetchType.EAGER)
	@JoinColumn(name = "FK_GROUP_ID")
	public Group getGroup() {
		return group;
	}
}

@Entity
@Table(name = "USER_GROUP")
public class Group {
	private int groupId;
	private String groupName;
	private String lastUpdatedBy;
	private Date lastUpdatedDate;

	public Group()
	{
	}

	@Id
	@GeneratedValue(strategy = IDENTITY)
	@Column(name = "PK_GROUP_ID", unique = true, nullable = false)
	public int getGroupId() {
		return groupId;
	}

	public void setGroupId(int groupId) {
		this.groupId = groupId;
	}

	@Column(name = "GROUP_NAME", nullable = true)
	public String getGroupName() {
		return groupName;
	}

	public void setGroupName(String groupName) {
		this.groupName = groupName;
	}

	@Column(name = "LAST_UPDATED_BY", nullable = false)
	public String getLastUpdatedBy() {
		return lastUpdatedBy;
	}

	public void setLastUpdatedBy(String lastUpdatedBy) {
		this.lastUpdatedBy = lastUpdatedBy;
	}

	@Column(name = "LAST_UPDATED_DATE", nullable = false)
	public Date getLastUpdatedDate() {
		return lastUpdatedDate;
	}

	public void setLastUpdatedDate(Date lastUpdatedDate) {
		this.lastUpdatedDate = lastUpdatedDate;
	}

	public String toString() {
		return this.groupId + "\t" + this.groupName + "\t\t" + this.lastUpdatedBy + "\t\t" + this.lastUpdatedDate;
	}


}

2. 外键双向(bidirectional with foreign key )
为Group 增加　User 变量

public class Group {
	...........
	private User user;


	................
	@OneToOne(mappedBy = "group")
	public User getUser() {
		return user;
	}

	public void setUser(User user) {
		this.user = user;
	}
	....................

}

group 是User类中的成员变量名。
mappedBy 作用如下：
[quote]
In a bidirectional relationship, one of the sides (and only one)
has to be the owner: the owner is responsible for
the association column(s) update.
To declare a side as not responsible
for the relationship,
the attribute mappedBy is used.
mappedBy refers to the property name of
the association on the owner side.
[/quote]
参考：[url]http://docs.jboss.org/ejb3/app-server/HibernateAnnotations/reference/en/html_single/index.html#d0e1517[/url]


3. 主键双向(bidirectional with primary key)

create table BODY(
	PK_BODY_ID	INT IDENTITY NOT NULL,
	LAST_UPDATED_BY	VARCHAR(50)	NOT NULL,
	LAST_UPDATED_DATE DATETIME NOT NULL
)

create table HEART(
	PK_HEART_ID	INT NOT NULL,
	HEART_TYPE		VARCHAR(50)	NOT NULL,
	LAST_UPDATED_BY	VARCHAR(50)	NOT NULL,
	LAST_UPDATED_DATE DATETIME NOT NULL
)

@Entity
@Table(name = "BODY")
public class Body {
	private Long id;
	private String lastUpdatedBy;
	private Date lastUpdatedDate;
	private Heart heart;

	public Body(){
	}

	@Id
	@GeneratedValue(strategy = GenerationType.IDENTITY)
	@Column(name = "PK_BODY_ID", unique = true, nullable = false)
	public Long getId() {
		return id;
	}

	public void setId(Long id) {
		this.id = id;
	}

	@OneToOne(cascade = CascadeType.ALL)
	@PrimaryKeyJoinColumn
	public Heart getHeart() {
		return heart;
	}

	public void setHeart(Heart heart) {
		this.heart = heart;
	}

	@Column(name = "LAST_UPDATED_BY", nullable = false)
	public String getLastUpdatedBy() {
		return lastUpdatedBy;
	}

	public void setLastUpdatedBy(String lastUpdatedBy) {
		this.lastUpdatedBy = lastUpdatedBy;
	}

	@Column(name = "LAST_UPDATED_DATE", nullable = false)
	public Date getLastUpdatedDate() {
		return lastUpdatedDate;
	}

	public void setLastUpdatedDate(Date lastUpdatedDate) {
		this.lastUpdatedDate = lastUpdatedDate;
	}

	public String toString() {
		return this.getId() + "\t" + this.getLastUpdatedBy() + "\t" + this.getLastUpdatedDate() + "\t" + this.getHeart().getId();
	}
}

@Entity
@Table(name = "HEART")
public class Heart {
	private Long id;
	private String type;
	private String lastUpdatedBy;
	private Date lastUpdatedDate;
	private Body body;

	public Heart() {
	}

	@Id
	@GenericGenerator(
name = "generator", 
strategy = "foreign", 
parameters = @Parameter(
   name = "property", 
   value = "body"))
	@GeneratedValue(generator="generator")
	@Column(name = "PK_HEART_ID", unique = true, nullable = false)
	public Long getId() {
		return id;
	}

	public void setId(Long id) {
		this.id = id;
	}

	@Column(name = "HEART_TYPE", nullable = false)
	public String getType() {
		return type;
	}

	public void setType(String type) {
		this.type = type;
	}

	@Column(name = "LAST_UPDATED_BY", nullable = false)
	public String getLastUpdatedBy() {
		return lastUpdatedBy;
	}

	public void setLastUpdatedBy(String lastUpdatedBy) {
		this.lastUpdatedBy = lastUpdatedBy;
	}

	@Column(name = "LAST_UPDATED_DATE", nullable = false)
	public Date getLastUpdatedDate() {
		return lastUpdatedDate;
	}

	public void setLastUpdatedDate(Date lastUpdatedDate) {
		this.lastUpdatedDate = lastUpdatedDate;
	}

	@OneToOne(cascade = CascadeType.ALL, mappedBy="heart")
	public Body getBody() {
		return body;
	}

	public void setBody(Body body) {
		this.body = body;
	}

	@Override
	public String toString() {
		return this.getId() + "\t" + this.getType();
	}
}

save时，　须调用

b.setHeart(h);
h.setBody(b);

否则会报错

Exception in thread "main" [size=xx-small]org.hibernate.id.IdentifierGenerationException: 
attempted to assign id from null one-to-one property: body[/size]

4. 主键单向没成功