Java SQL JPA - 多列作为主键
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SQL JPA - Multiple columns as primary key
提问by Anders Pedersen
If i want severeal Column to make up an ID.
如果我想要严重的列来组成一个 ID。
SQL example :
SQL 示例：
CONSTRAINT [PK_NAME] PRIMARY KEY ([Column1],[Column2],[Column3])
How can i do that with a Jpa Entity class ? through columndefinition ?
我怎么能用 Jpa 实体类做到这一点？通过列定义？
just setting the id field as:
只需将 id 字段设置为：
value = Column1 + Column2 + Column3 // aint working.
采纳答案by Raul Cuth
You need to have a class for your composite key:
您需要为复合键创建一个类：
public class CompositeKey implements Serializable {
private int column1;
private int column2;
private int column3;
}
and then in your entity class use the @IdClassannotation:
然后在您的实体类中使用@IdClass注释：
@Entity
@IdClass(CompositeKey.class)
public class EntityExample {
@Id
private int column1;
@Id
private int column2;
@Id
private int column3;
...
...
}
I think this should work. Hope it helps, cheers!
我认为这应该有效。希望能帮到你，加油！
Yea and there is the other solution, the one that @jklee mentioned, both work, it's a matter of preference.
是的，还有另一种解决方案，@jklee 提到的那个，两者都有效，这是一个偏好问题。
回答by Penguin
- Using
@IdClassannotation on the@Entityclass followed by@Idannotation on individual fields that are part of composite primary key. - Alternatively can make use of
@Embeddableclass which can consist of individual fields of the composite primary key and then a reference of this class can be used as an attribute with@Embeddedannotation in@Entityclass. Hope this helps.
@IdClass在@Entity类上使用注释，然后@Id在作为复合主键一部分的各个字段上使用注释。- 或者，可以使用
@Embeddable由复合主键的各个字段组成的类，然后可以将此类的引用用作类中带有@Embedded注释的属性@Entity。希望这可以帮助。
回答by jklee
Use @Embeddableand @EmbeddedId.
使用@Embeddable和@EmbeddedId。
Example:
例子：
@Entity
public class Project {
@EmbeddedId ProjectId id;
:
}
@Embeddable
Class ProjectId {
int departmentId;
long projectId;
}
More information here http://www.objectdb.com/java/jpa/entity/id#Embedded_Primary_Key_
更多信息在这里http://www.objectdb.com/java/jpa/entity/id#Embedded_Primary_Key_
回答by heroin
If all fields in the class are part of primary key, then solution would be pretty simple (extending solution provided by @raul-cuth):
如果类中的所有字段都是主键的一部分，那么解决方案将非常简单（扩展解决方案由@raul-cuth 提供）：
@Entity
@IdClass(EntityExample.class)
public class EntityExample implements Serializable {
@Id
private int column1;
@Id
private int column2;
@Id
private int column3;
}
回答by user577736
Be aware that the hibernate Entity-Class-to-SQL-DDL-Script generator will sort all the fields, and irrespective of the order in which it appears in the definitions, will create the table definition and the index / constraint definitions in this sorted order of the fields.
请注意，hibernate Entity-Class-to-SQL-DDL-Script 生成器将对所有字段进行排序，并且无论它在定义中出现的顺序如何，都将在此排序中创建表定义和索引/约束定义字段的顺序。
While the order of appearance of the fields in the table definition may not matter much, the order of fields in a composite index definitely do. So your key-fields must be named so that when sorted by their names they are in the order you desire for the index).
虽然表定义中字段的出现顺序可能无关紧要，但复合索引中字段的顺序确实很重要。因此，您的关键字段必须命名，以便按名称排序时，它们会按您希望的索引顺序排列）。
