每个具体类继承混合联接和表 [英] Mixing Joined and Table per concrete class inheritance

问题描述

我有A，B，C，D，E和F类，其中 B从A延伸，C从B延伸 D从A延伸，E从D延伸 F从A延伸.

I have classes A, B, C, D, E and F where B extends from A, C extends from B D extends from A, E extends from D F extends from A.

我想根据B，D和F级别的每个具体类继承策略在A和Table使用Joined继承策略. A，B和D是抽象类，而C，E和F是具体类.

I want to use Joined inheritance strategy at A and Table per concrete class inheritance strategy from B,D and F level. A,B and D are abstract classes and C,E and F are concrete classes.

这有可能吗，如果是的话，我们应该怎么做.当我尝试时，最终会为所有6个类获得单独的表，并且我希望创建4个表(一个分别用于A，三个分别用于C，E和F).

Is this possible and if yes how should we do it. When I try, I end up getting separate tables for all 6 classes and I want 4 tables to get created (one for A and 3 for C,E and F respectively).

我在类A中使用了@Inheritance(strategy = InheritanceType.JOINED) B，D和F类中的@Inheritance(strategy = InheritanceType.TABLE_PER_CLASS)

I used @Inheritance(strategy = InheritanceType.JOINED) in class A and @Inheritance(strategy = InheritanceType.TABLE_PER_CLASS) in classes B,D and F

我看到了一些示例，将每个层次结构的表混合在一起，并加入了继承策略，但是我想实现上面提到的内容而不使用每个层次结构的表.

I have seen examples to mix table per hierarchy and joined inheritance strategies but I want to implement what I mentioned above without using table per hierarchy.

请帮帮我.

推荐答案

这有点晚了，但是最近我遇到了类似的问题.我发现的解决方案是在不需要单独表的抽象类上使用@MappedSuperclass批注.

This is a bit late, but I had a similar problem recently. The solution that I found is to use @MappedSuperclass annotation on the abstract classes for which you don't want separate tables.

例如

@Entity(name = "A")
@Inheritance(strategy = InheritanceType.JOINED)
public class A {
    // mapped fields that go into parent A table
}

@MappedSuperclass
public class B extends A {
    // fields that should get pushed down to tables that inherit from B
}

@MappedSuperclass
public class D extends A {
    // fields that should get pushed down to tables that inherit from D
}

@Entity(name = "F"
public class F extends A {
    // fields that are specific to table F
}

@Entity(name = "C")
public class C extends B {
    // fields that are specific to table C 
}

@Entity(name = "E")
public class E extends D {
    // fields that are specific to table E
}

这假定您在@MappedSuperclass类中应用的映射(尤其是列名)对于子类表是相同的.如果不是，则需要在类上使用@AttributeOverride批注.例如，

This assumes that the mappings that you apply in the @MappedSuperclass classes (in particular, the column names) are the same for the subclass tables. If they aren't, you need to use the @AttributeOverride annotation on the class. For example,

@MappedSuperclass // this insures that no table is created for this class, but that the mapped fields are pushed down to the subclasses.
public class B extends A {
    @Id @Generated
    @Column(name = "myId")
    public int myId;
}

@Entity(name = "C")
@AttributeOverride(name = "myId", column = @Column(name = "ID"))
public class C extends B {

}

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