今天又深入了了解和測試了一下Hibernate cascade 和 inverse 。

Inverse

在Hibernate annotation 中inverse 默認(rèn)值是"true" 當(dāng)配置了mappedBy="…"時就相當(dāng)于inverse="false"了。

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 {

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????private String id;

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????private Rose rose;

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????public User() {

????}

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????@Id

????@Column(name = "Id", unique = true, nullable = false, insertable = true, updatable = true, length = 5)

????public String getId() {

????????return this.id;

????}

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????public void setId(String id) {

????????this.id = id;

????}

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????@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;

????}

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????public void setRose(Rose rose) {

????????this.rose = rose;

????}

}

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@Entity

@Table(name = "Rose")

public class Rose implements java.io.Serializable {

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????private String id;

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????private Set<User> users = new HashSet<User>(0);

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????public Rose() {

????}

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????@Id

????@Column(name = "Id", unique = true, nullable = false, insertable = true, updatable = true, length = 3)

????public String getId() {

????????return this.id;

????}

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????public void setId(String id) {

????????this.id = id;

????}

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????@OneToMany(cascade = { CascadeType.ALL }, fetch = FetchType.EAGER )

????@JoinColumn(name="RoseId")

????public Set<User> getUsers() {

????????return this.users;

????}

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????public void setUsers(Set<User> userses) {

????????this.users = userses;

????}

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????public void addUser(User user) {

????????user.setRose(this);

????????users.add(user);

????}

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當(dāng)在user類中配置成cascade = { CascadeType.PERSIST, CascadeType.MERGE } 時，更新和刪除兩個級聯(lián)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：

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???????? 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(shù)據(jù)庫不加級聯(lián)限制

????????userDao.delete(user);

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當(dāng)在user類中配置成cascade = { CascadeType.ALL } or cascade={} 時，無法刪除。

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更新時也類似于這種情況，注意rose類中的addUser(User user)方法。

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再有fetch = FetchType.EAGER。在這里不是延時加載，如果設(shè)置成LAZY,在取得數(shù)據(jù)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。。。