嵌套单表继承

Question

我遇到了对象模型和 Hibernate 的问题。我希望将整个模型存储为单个表。

我已经尝试了以下方法，但是当我要求 Hibernate 生成 SQL 创建文件时，它会创建 3 个表而不是只有 1 个。类层次结构可能看起来很奇怪，但它当然是脱离上下文的 :)

尝试 1：

@MappedSuperclass
@Inheritance(strategy = InheritanceType.SINGLE_TABLE)
@DiscriminatorColumn(name = "CATEGORY", discriminatorType = DiscriminatorType.STRING, length  = 10)
@Table(name = "the_table")
public abstract class A {}

@MappedSuperclass
@DiscriminatorValue(value = "B")
@Inheritance(strategy = InheritanceType.SINGLE_TABLE)
@DiscriminatorColumn(name = "TYPE", discriminatorType = DiscriminatorType.STRING, length = 20)
public abstract class B extends A {}

@Entity
@DiscriminatorValue(value = "X")
public class X extends B {}

@Entity
@DiscriminatorValue(value = "Y")
public class Y extends B {}

@Entity
@DiscriminatorValue(value = "Z")
public class Z extends B {}

尝试 2： 我们到了那里，不是它创建了 1 个表，而是没有生成鉴别器列。有人能发现错误吗？

@Entity
@Inheritance(strategy = InheritanceType.SINGLE_TABLE)
@DiscriminatorColumn(name = "CATEGORY", discriminatorType = DiscriminatorType.STRING, length  = 10)
@DiscriminatorFormula(value = "CATEGORY || '_' || TYPE")
@Table(name = "the_table")
public abstract class A {}

@Entity
@DiscriminatorColumn(name = "TYPE", discriminatorType = DiscriminatorType.STRING, length = 20)
public abstract class B extends A {}

@Entity
@DiscriminatorValue(value = "B_X")
public class X extends B {}

@Entity
@DiscriminatorValue(value = "B_Y")
public class Y extends B {}

@Entity
@DiscriminatorValue(value = "B_Z")
public class Z extends B {}

Answer 1

删除@MappedSuperclass 并尝试。此外，您不能在一个层次结构中使用两次 @Inheritance 标记 - 只会使用一个。

如果您想使用多个列作为鉴别器，请使用@DiscriminatorFormula

@Entity
@Inheritance(strategy = InheritanceType.SINGLE_TABLE)
@DiscriminatorForumula("CATEGORY || '_' || TYPE")
public abstract class A 

@Entity
@DiscriminatorValue(value = "B_X")
public class X extends A {}

@Entity
@DiscriminatorValue(value = "B_Y")
public class Y extends A {}

@Entity
@DiscriminatorValue(value = "B_Z")
public class Z extends A {}