淺析Hibernate集合映射inverse和cascade
作者：佚名
在Hibernate annotation 中inverse 默認值是"true" 當配置了mappedBy="…"時就相當于inverse="false"了。CascadeType類中有這樣幾個常量，ALL、PERSIST、MERGE、REFRESH、REMOVE 。
Hibernate有很多值得學習的地方，這里我們主要了解和測試Hibernate cascade和Hibernate inverse，希望對大家的學習有所幫助。
1: Hibernate inverse
在Hibernate annotation 中inverse 默認值是"true" 當配置了mappedBy="…"時就相當于inverse="false"了。
2: Hibernate cascade
CascadeType類中有這樣幾個常量，ALL、PERSIST、MERGE、REFRESH、REMOVE 。
讓代碼說話吧：
- @Entity
- @Table(name = "Users")
- public class User implements java.io.Serializable {
- private String id;
- private Rose rose;
- public User() {
- }
- @Id
- @Column(name = "Id", unique = true, nullable = false, insertable = true, updatable = true, length = 5)
- public String getId() {
- return this.id;
- }
- public void setId(String id) {
- this.id = id;
- }
- @ManyToOne(cascade = { CascadeType.PERSIST, CascadeType.MERGE }, fetch = FetchType.LAZY)
- @JoinColumn(name = "Roseid", unique = false, nullable = false, insertable = true, updatable = true)
- public Rose getRose() {
- return this.rose;
- }
- public void setRose(Rose rose) {
- this.rose = rose;
- }
- }
- @Entity
- @Table(name = "Rose")
- public class Rose implements java.io.Serializable {
- private String id;
- private Set<User> users = new HashSet<User>(0);
- public Rose() {
- }
- @Id
- @Column(name = "Id", unique = true, nullable = false, insertable = true, updatable = true, length = 3)
- public String getId() {
- return this.id;
- }
- public void setId(String id) {
- this.id = id;
- }
- @OneToMany(cascade = { CascadeType.ALL }, fetch = FetchType.EAGER )
- @JoinColumn(name="RoseId")
- public Set<User> getUsers() {
- return this.users;
- }
- public void setUsers(Set<User> userses) {
- this.users = userses;
- }
- public void addUser(User user) {
- user.setRose(this);
- users.add(user);
- }
當在user類中配置成cascade = { CascadeType.PERSIST, CascadeType.MERGE } 時，更新和刪除兩個級聯時:
- Hibernate: select user_.Id, user_.Enabledel as Enabledel1_, user_.Name as Name1_, user_.Password as Password1_, user_.Roseid as Roseid1_ from ERP.dbo.Users user_ where user_.Id=?
- Hibernate: select rose_.Id, rose_.Enabledel as Enabledel0_, rose_.Name as Name0_, rose_.Parent as Parent0_ from ERP.dbo.Rose rose_ where rose_.Id=?
- Hibernate: delete from ERP.dbo.Users where Id=?
可以正常刪除！但是代碼要這樣寫：
- User user =new User("adm");
- user.setRose(new Rose("adm")); //這句不加就不能刪除，提示錯誤。除非數據庫不加級聯限制
- userDao.delete(user);
當在user類中配置成cascade = { CascadeType.ALL } or cascade={} 時，無法刪除。更新時也類似于這種情況，注意rose類中的addUser(User user)方法。再有fetch = FetchType.EAGER。在這里不是延時加載，如果設置成LAZY,在取得數據時怎么做好呢？看其他論壇的方法各有好處也有不好的地方，在找一個更方法。。。
【編輯推薦】
責任編輯：仲衡
來源：
blogjava
