這是個(gè)系列教程，看完這個(gè)世杀，你對(duì)JavaEE注解，包括spring肝集、hibernate瞻坝，RESTFul web service ，JAXB, 以及junit注解將會(huì)有一個(gè)全面的了解杏瞻。
英文原版網(wǎng)址在這里 我們不光是spring網(wǎng)站的搬運(yùn)工@農(nóng)夫山泉水所刀，實(shí)際上，翻譯過程中我保證準(zhǔn)確同時(shí)捞挥，加入了自己的理解浮创。

Hibernate JPA Annotations - Contents:

@Entity
import javax.persistence.Entity;

@Table
import javax.persistence.Table;

@Column
import javax.persistence.Column;

@Id
import javax.persistence.Id;

@GeneratedValue
import javax.persistence.GeneratedValue;

@Version
import javax.persistence.Version;

@OrderBy
import javax.persistence.OrderBy;

@Transient
import javax.persistence.Transient;

@Lob
import javax.persistence.Lob;

Hibernate Association Mapping Annotations

@OneToOne
import javax.persistence.OneToOne;

@ManyToOne
import javax.persistence.ManyToOne;

@OneToMany
import javax.persistence.OneToMany;

@ManyToMany
import javax.persistence.ManyToMany;

@PrimaryKeyJoinColumn
import javax.persistence.PrimaryKeyJoinColumn;

@JoinColumn
import javax.persistence.JoinColumn;

@JoinTable
import javax.persistence.JoinTable;

@MapsId
import javax.persistence.MapsId;

Hibernate Inheritance Mapping Annotations

@Inheritance
import javax.persistence.Inheritance;

@DiscriminatorColumn
import javax.persistence.DiscriminatorColumn;

@DiscriminatorValue
import javax.persistence.DiscriminatorValue;

@Entity,@Table,@Colume,@Id,@GeneratedValue略

@OrderBy（用于One-to-Many等關(guān)聯(lián)表中集合的排序）

@OrderBy("firstName asc")
private Set contacts;

@Transient 字段不會(huì)更新到數(shù)據(jù)庫

@Lob：二進(jìn)制數(shù)據(jù)

hibernate的注解就這么完了嗎？

Paste_Image.png

hibernate注解的<u>重難點(diǎn)</u>在于多表之間的關(guān)系：

栗子來了：

Paste_Image.png

company - companydetail : one-to-one砌函，共享相同主鍵
contact - contactDetail : 通過外鍵連接的one-to-one
contact-company : 外鍵連接的many-to-one, contact作為owner
company-companyStatus : 外鍵連接的many-to-one斩披，company作為owner

one-to-one tips：

共享相同主鍵的用@PrimaryKeyJoinColumn
一方持有另一方外鍵，用 @JoinColumn & @OneToOne和 mappedBy屬性
兩個(gè)Entity通過一個(gè)中間表聯(lián)系讹俊，使用@JoinTable and mappedBy
共享鍵用@MapsId

one-to-one

@Entity
@Table(name = "company")
public class Company implements Serializable {
   
  @Id
  @Column(name = "id")
  @GeneratedValue
  private int id;
   
  @OneToOne(cascade = CascadeType.MERGE)
  @PrimaryKeyJoinColumn
  private CompanyDetail companyDetail;
   
  ...
}
 
@Entity
@Table(name = "companyDetail")
public class CompanyDetail implements Serializable {
 
  @Id
  @Column(name = "id")
  private int id;
   
  ...
}



@Entity
@Table(name = "contactDetail")
public class ContactDetail implements Serializable {
 
  @Id
  @Column(name = "id")
  @GeneratedValue
  private int id;
   
  @OneToOne
  @MapsId
  @JoinColumn(name = "contactId")
  private Contact contact;
   
  ...
}
 
@Entity
@Table(name = "contact")
public class Contact implements Serializable {
 
  @Id
  @Column(name = "ID")
  @GeneratedValue
  private Integer id;
 
  @OneToOne(mappedBy = "contact", cascade = CascadeType.ALL)
  private ContactDetail contactDetail;
 
  ....
}

cascade(級(jí)聯(lián))級(jí)聯(lián)在編寫觸發(fā)器時(shí)經(jīng)常用到垦沉，觸發(fā)器的作用是當(dāng) 主控表信息改變時(shí)，用來保證其關(guān)聯(lián)表中數(shù)據(jù)同步更新仍劈。若對(duì)觸發(fā)器來修改或刪除關(guān)聯(lián)表相記錄厕倍，必須要?jiǎng)h除對(duì)應(yīng)的關(guān)聯(lián)表信息，否則贩疙，會(huì)存有臟數(shù)據(jù)讹弯。所以，適當(dāng)?shù)淖龇ㄊ钦饨Γ瑒h除主表的同時(shí)组民，關(guān)聯(lián)表的信息也要同時(shí)刪除，在hibernate中芍躏，只需設(shè)置cascade屬性值即可邪乍。

CascadeType.PERSIST：級(jí)聯(lián)新增（又稱級(jí)聯(lián)保存）：對(duì)order對(duì)象保存時(shí)也對(duì)items里的對(duì)象也會(huì)保存。對(duì)應(yīng)EntityManager的presist方法

例子：只有A類新增時(shí)，會(huì)級(jí)聯(lián)B對(duì)象新增庇楞。若B對(duì)象在數(shù)據(jù)庫存（跟新）在則拋異常（讓B變?yōu)槌志脩B(tài)）

CascadeType.MERGE:級(jí)聯(lián)合并（級(jí)聯(lián)更新）：若items屬性修改了那么order對(duì)象保存時(shí)同時(shí)修改items里的對(duì)象榜配。對(duì)應(yīng)EntityManager的merge方法

例子：指A類新增或者變化，會(huì)級(jí)聯(lián)B對(duì)象（新增或者變化）

CascadeType.REMOVE:級(jí)聯(lián)刪除：對(duì)order對(duì)象刪除也對(duì)items里的對(duì)象也會(huì)刪除吕晌。對(duì)應(yīng)EntityManager的remove方法

例子：REMOVE只有A類刪除時(shí)蛋褥，會(huì)級(jí)聯(lián)刪除B類；

CascadeType.REFRESH:級(jí)聯(lián)刷新：獲取order對(duì)象里也同時(shí)也重新獲取最新的items時(shí)的對(duì)象睛驳。對(duì)應(yīng)EntityManager的refresh(object)方法有效烙心。即會(huì)重新查詢數(shù)據(jù)庫里的最新數(shù)據(jù) （用的比較少）

CascadeType.ALL:以上四種都是

綜上所述：一般的，用CascadeType.MERGE:級(jí)聯(lián)合并（級(jí)聯(lián)更新）就能達(dá)到級(jí)更新同時(shí)又穩(wěn)定不報(bào)錯(cuò)乏沸。

@ManyToOne

tips:
Use @JoinColumn when foreign key is held by one of the entities.
Use @JoinTable for entities linked through an association table.

@Entity
@Table(name = "contact")
public class Contact implements Serializable {
 
  @ManyToOne
  @JoinColumn(name = "companyId")
  private Company company;
   
  ...
   
 }
 
@Entity
@Table(name = "company")
public class Company implements Serializable {
 
  @ManyToOne
  @JoinColumn(name = "statusId")
  private CompanyStatus status;
   
  ...
   
 }

@OneToMany

tips:
Use mappedBy attribute for bi-directional associations with ManyToOne being the owner.
OneToMany being the owner or unidirectional with foreign key - try to avoid such associations but can be achieved with @JoinColumn
@JoinTable for Unidirectional with association table

//Please see the many-to-one relationship between Contact and Company above. Company to Contact will be a one-to-many relationship. The owner of this relationship is Contact and hence we will use 'mappedBy' attribute in Company to make it bi-directional relationship.
@Entity
@Table(name = "company")
public class Company implements Serializable {
 
  @OneToMany(mappedBy = "company", fetch = FetchType.EAGER)
  @OrderBy("firstName asc")
  private Set contacts;
     
  ...
   
 }

@ManyToMany

tips:
Use @JoinTable for entities linked through an association table.
Use mappedBy attribute for bi-directional association.