Question

我已经利用“遗产”规划了我在解放国的继承等级。区分不同实体的单列可变和分立栏。超级楼的所有子级都将其田地储存到二级表。例如:

@MappedSuperclass
public abstract class Base
{
   @Id 
   private String id;

   @Version
   private long version;
}

@Entity
@Inheritance(strategy = InheritanceType.SINGLE_TABLE)
@DiscriminatorColumn(name = "type", discriminatorType = DiscriminatorType.STRING) 
public class Parent extends Base
{
    @Column(nullable=false)
    private BigDecimal value;
}

@Entity
@DiscriminatorValue("child1")
@SecondaryTable(name = "Child1")
public class Child1 extends Parent
{
     @Column(table="Child1")
     private String name;
}

@Entity
@DiscriminatorValue("child2")
@SecondaryTable(name = "Child2")
public class Child2 extends Parent
{
     @Column(table="Child2")
     private String name2;
}

I now have an Entity that has a @OneToOne relationship with the Parent class. This Entity only needs to work with the value field from the Parent class. It will never need to work with any fields from any subclass of Parent

@Entity
public class AnotherEntity extends Base
{
    @JoinColumn(name="parentId")
    @OneToOne(fetch=FetchType.Lazy, optional=true, targetEntity=Parent.class)
    private Parent parent;
 }

我想要的是,只有父母的领域。当与父母的关系从数据库中填满时,就选定班级。我看到的是,自由主义企图把扩大父母的实体的所有财产装上。它还加入了所有中学。问题在于我有30个扩大父母的实体。这使父母实体无法摆脱困境,因为查询过程是30个。

例如,我看到的那类问题就是:

Hibernate: 
select
    parent.id as id3_0_,
    parent_.version as version3_0_,
    parent.name1 as name110_3_0_,
    parent.name2 as name24_3_0_,
    parent.type as type3_0_ 
from
    Parent parent0_ 
left outer join
    Child1 parent0_2_ 
        on parent0_.id=parent0_2_.id 
left outer join
    Child2 parent0_3_ 
        on parent0_.id=parent0_3_.id

我不理解为什么赫尔辛基决定选择父母子类中界定的所有财产的超级集,并加入所有二级表? 我可以理解,它加入了由提及父母的处分者价值确定的实体的次要表格,但我感到困惑。

我的问题是,我如何满足我的要求,即在我恢复另一个爱情阶层的父母关系时,只能把来自父母阶层的田地装上?

感谢。

Answer 1

二级表格通常用于将单一实体的内容绘制到两个表格。它利用日本广播公司的标准说明,允许进行zy/电子计算。只有在必要的情况下,才可使用专有的排他性通知,以单独的方式装载。见:

fetch: If set to JOIN, the default, Hibernate will use an inner join to retrieve a secondary table defined by a class or its superclasses and an outer join for a secondary table defined by a subclass. If set to SELECT then Hibernate will use a sequential select for a secondary table defined on a subclass, which will be issued only if a row turns out to represent an instance of the subclass. Inner joins will still be used to retrieve a secondary defined by the class and its superclasses.

因此,确定<代码>fetch属性:@Table注改为SlectT将做你想要做的事:将再发布一个选择条款,从适当的次要表格中挑选数值。

如果你想要 la,那么一个次要的表格不是你想要的。你们不得不利用协会这样做。

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