子类如何覆盖继承的关联的映射，以便将其忽略(未为子类实体映射)? [英] How can a subclass override the mapping of an inherited association so that it is ignored (not mapped for the subclass entity)?

问题描述

给出一些这样的实体:

@MappedSuperclass
public abstract class BaseEntity {
    @ManyToOne(optional = true)
    @JoinColumn(name = "friend_id")
    private AnotherEntity friend;
}

@Entity
public class AnotherEntity {
    // ...
}

@Entity
public class ConcreteEntity extends BaseEntity {
    //...
}

ConcreteEntity如何覆盖friend的映射，以便对于ConcreteEntity的实例完全不映射?

How can ConcreteEntity override the mapping of friend so that it is not mapped at all for instances of ConcreteEntity?

推荐答案

通常，在实体中，您可以使用@AssociationOverrides批注覆盖@MappedSuperclass中的关系(元素)，但是要强制执行忽略它.为此，存在@Transient批注，但它不会指示JPA提供程序忽略重写的属性.因此，恕我直言，只有一种可能性:定义一个没有这种关系的SupperMappedClass，并在您的类层次结构中使用它:

In general in an entity you can override (elements of) a relationship from a @MappedSuperclass using the @AssociationOverrides annotation, but what you want is to force ignoring it. For that there is the @Transient annotation, but which does not instruct the JPA provider to ignore the overridden property. So you have IMHO a single possibility: defining a SupperMappedClass without that relationship and use that in your class hierarchy:

@MappedSuperclass
public abstract class BaseEntityWithoutFriend {

}


@MappedSuperclass
public abstract class BaseEntityWithFriend {
    @ManyToOne(optional = true)
    @JoinColumn(name = "friend_id")
    private AnotherEntity friend;
}


@Entity
public class ConcreteEntity extends BaseEntityWithoutFriend {//NOTE here that we extend the EntityWithoutFriend
    //...
}

注意:根据我对Hibernate的经验，在您的实体中添加属性@Transient AnotherEntity friend只会强制仅映射MappedSupperClass朋友属性，而仅忽略ConcreteEntity中定义的属性.

NOTE: as of my experience with Hibernate, adding a property @Transient AnotherEntity friend in your entity will simply force mapping only MappedSupperClass friend property, ignoring only the property defined in ConcreteEntity.

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