java JPA 或 Hibernate 生成（非主键）列值，而不是从 1 开始
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JPA or Hibernate to generate a (non primary key) column value, not starting from 1
提问by mist
I want a JPA/Hibernate (preferably JPA) annotation that can generate the value of a column, that is not a primary key and it doesn't start from 1.
我想要一个可以生成列值的 JPA/Hibernate（最好是 JPA）注释，它不是主键，也不是从 1 开始。
From what I have seen JPA cannot do that with @GeneratedValue and @SequenceGenerator and @TableGenerator. Or with anything else.
从我所看到的 JPA 不能用 @GeneratedValue 和 @SequenceGenerator 和 @TableGenerator 做到这一点。或与其他任何东西。
I have seen a solutionwith an extra table, which I find is not elegant.
我见过一个带有额外桌子的解决方案，我发现它并不优雅。
I can live with a Hibernate annotation, because I already have hibernate annotations.
我可以忍受 Hibernate 注释，因为我已经有了 Hibernate 注释。
I want to use @Generated but I cannot make it work and people claimthat it is possible.
我想使用 @Generated 但我无法让它工作，人们声称这是可能的。
@Generated(GenerationTime.INSERT)
private long invoiceNumber;//invoice number
Update: an extra requirement, if the transaction is rolled back, we can't have a gap in the numbering. Anyone?
更新：一个额外的要求，如果事务回滚，我们不能在编号上有间隙。任何人？
采纳答案by mist
Here's what worked for me - we coded all of it in the service. Here's the entity:
这对我有用 - 我们在服务中编码了所有这些。这是实体：
@Entity
@Inheritance(strategy = InheritanceType.SINGLE_TABLE)
public class Registrant extends AbstractEntity {
//....
private long invoiceNumber;//invoice number
@Entity
public static class InvoiceNumberGenerator {
@Id
@GeneratedValue
private int id;
private long counter;
public int getId() {
return id;
}
public void setId(int id) {
this.id = id;
}
public long getCounter() {
return counter;
}
public void setCounter(long counter) {
this.counter = counter;
}
}
}
And then we have a service that does the magic (actually there's no magic, all is done manually):
然后我们有一个服务可以施展魔法（实际上没有魔法，一切都是手动完成的）：
public synchronized Registrant save(Registrant registrant) {
long counter = getInvoiceNumber();
registrant.setInvoiceNumber(counter);
return registrantRepository.save(registrant);
}
private long getInvoiceNumber() {
//mist: get the invoice number from the other table
long count = registrantInvoiceNumberGeneratorRepository.count();
if(count > 1) {
throw new RuntimeException(": InvoiceNumberGenerator table has more than one row. Fix that");
}
Registrant.InvoiceNumberGenerator generator;
if(count == 0) {
generator = new Registrant.InvoiceNumberGenerator();
generator.setCounter(1000001);
generator = registrantInvoiceNumberGeneratorRepository.save(generator);
} else {
generator = registrantInvoiceNumberGeneratorRepository.findFirstByOrderByIdAsc();
}
long counter = generator.getCounter();
generator.setCounter(counter+1);
registrantInvoiceNumberGeneratorRepository.save(generator);
return counter;
}
Note the synchronizedmethod - so that nobody can get the same number.
注意synchronized方法 - 这样没有人可以获得相同的数字。
I can't believe there's nothing automatic that can do that.
我不敢相信没有什么自动可以做到这一点。
回答by Vlad Mihalcea
The @GeneratedValueonly works for identifiers and so you can't use it. If you use MySQL, you are quite limited, since database sequences are not supported.
该@GeneratedValue只适用于标识符，所以你不能使用它。如果您使用 MySQL，您将受到很大限制，因为不支持数据库序列。
InnoDB doesn't support multiple AUTO_INCREMENT columnsand if your table PK is AUTO_INCREMENTED, then you have two options:
InnoDB不支持多个 AUTO_INCREMENT 列，如果您的表 PK 是 AUTO_INCREMENTED，那么您有两个选择：
Go for a separate table that behaves like a sequence generator, the solution you already said you are not happy about.
Use an INSERT TRIGGERto increment that column.
寻找一个单独的表，它的行为类似于序列生成器，这是您已经说过不满意的解决方案。
使用INSERT TRIGGER增加该列。
