不能使用 < union-subclass > (TABLE_PER_CLASS)的标识列键生成

超级班:

@Entity
@Inheritance(strategy = InheritanceType.TABLE_PER_CLASS)
public abstract class SuperClass implements Serializable {
private static final long serialVersionUID = -695503064509648117L;


long confirmationCode;


@Id
@GeneratedValue(strategy = GenerationType.AUTO) // Causes exception!!!
public long getConfirmationCode() {
return confirmationCode;
}


public void setConfirmationCode(long confirmationCode) {
this.confirmationCode = confirmationCode;
}
}

类别:

@Entity
public abstract class Subclass extends SuperClass {
private static final long serialVersionUID = 8623159397061057722L;


String name;


@Column(nullable = false)
public String getName() {
return name;
}


public void setName(String name) {
this.name = name;
}
}

给了我这个例外:

Caused by: org.hibernate.MappingException: Cannot use identity column key
generation with <union-subclass> mapping for: com.something.SuperClass

对我来说，生成身份证的最好和最方便的方法是什么

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最佳答案

The problem here is that you mix "table-per-class" inheritance and GenerationType.Auto. Consider an identity column in MsSQL. It is column based. In a "table-per-class" strategy you use one table per class and each one has an ID.

Try:

@GeneratedValue(strategy = GenerationType.TABLE)

小开

I wonder if this is a database dialect specific problem, since watching a youtube tutorial with PostgreSQL as the underlying database I saw that the creator of the video run succefully an app with the default @GeneratedValue. In my case (the underlying database is MySQL) I had to modify the @GeneratedValue strategy to GenerationType.TABLE exactly as zoidbeck proposes.

Here is the video : https://www.youtube.com/watch?v=qIdM4KQOtH8

小开

In our case, we use a PostreSQL database for dev and production and an in-memory hsqldb database for tests. We are using a sequence in both cases to generate an id. Apparently GenerationType.AUTO defaults to SEQUENCE for postgres, but failed in our local tests (must default to something else for hsqldb).

So the solution that worked for us, explicitly use GenerationType.SEQUENCE.

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Agree with zoidbeck's answer. You need to change strategy to:

@GeneratedValue(strategy = GenerationType.TABLE)

But that's not all, you need to create a new table, what will hold your abstract's table primary key sequence. Modify your mapping to

@Id
@GeneratedValue(strategy = GenerationType.TABLE, generator = "ConfirmationCodeGenerator")
@TableGenerator(table = "SEQUENCES", name = "ConfirmationCodeGenerator")
public long getConfirmationCode() {
return confirmationCode;
}

And a new table in database should look like following: enter image description here

When you ran your application, Hibernate will insert a row where sequence_name will be the entity name (SuperClass in this example) and sequence_next_hi_value value will be automatically incremented and used for new records of all implementing subclasses's tables.

小开

you can use @MappedSuperclass for inheritance


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