[英]Using Hibernate Get with Multi-Column Primary Key
假設我有一個看起來像這樣的類:
public class MyClass {
@Id
@Column(name = "ID")
private long Id;
}
我可以使用休眠會話對類進行獲取或加載,如下所示:
MyClass a = (MyClass)session.get(MyClass.class, new Long(100));
但是,假設我有一個以多列為主鍵的類:
public MyJoinClass implements Serializable {
private static final long serialVersionUID = -5L;
@Id
@Column(name = "ID")
private long id;
@Id
@Column(name = "EMAIL_ADDRESS_ID")
private long emailAddressId;
}
是否可以對這樣的類使用 get 或 load?
嘗試使用@IdClass
或@EmbeddedId
public MyJoinClass implements Serializable {
private static final long serialVersionUID = -5L;
@EmbeddedId
private MyJoinClassKey key;
}
public MyJoinClassKey implements Serializable{
@Column(name = "ID")
private long id;
@Column(name = "EMAIL_ADDRESS_ID")
private long emailAddressId;
}
然后使用
MyJoinClass a = (MyJoinClass )session.get(MyJoinClass .class, new MyJoinClassKey (1, "email"));
看一看這個問題, 這被廣泛解釋。 基本上休眠有復合鍵的機制。
在 Hibernate 中是( 文檔):
MyJoinClass a = session.get(MyJoinClass.class, new MyJoinClass(100, 200));
只要確保有一個包含復合鍵所有部分的構造函數(不要忘記沒有參數的默認公共構造函數):
public MyJoinClass implements Serializable {
private static final long serialVersionUID = -5L;
@Id
@Column(name = "ID")
private long id;
@Id
@Column(name = "EMAIL_ADDRESS_ID")
private long emailAddressId;
public MyJoinClass() {}
public MyJoinClass(long id, long emailAddressId) {
this.id= id;
this.emailAddressId= emailAddressId;
}
}
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