对于此实体层次结构，什么是好的持久性设计? [英] What is a good persistence design for this entity hierarchy?

问题描述

我是JPA的新手，正在尝试为以下课程设计设计.所有类都具有equals和覆盖的hashcode，getters和setter以及空的构造函数.

I'm new to JPA and trying to work out the design for the following classes. All classes have equals and hashcode overriden, getters and setter and empty constructor.

我对所有实体都有一个基类:

I have a base class for all entities:

public abstract class BaseEntity {
    protected Point loc;
    protected List<Property> properties = new ArrayList<>();
}

Point类只是标准的x-y持有人

The Point class is just the standard x-y holder

public class Point {
    private int x, y;
}

Property类包含一个名称和一个id:

And the Property class holds a name and an id:

public class Property {
    private int id;
    private String name;
}

有3个类继承自BaseEntity.第一个是House.一所房子可以容纳一个单人家庭.

There are 3 classes that inherit from BaseEntity. The first one is House. A House can hold a single family.

public class House extends BaseEntity {
    private Family family;
}

public class Tree extends BaseEntity {
    private String name;
}

家庭很快就会出现.第二个是所有生物实体的超类:

Family will be show soon. The second one is the superclass for all the living entities:

public abstract class LivingEntity extends BaseEntity {
    public static enum Status { ALIVE, DECEASED }
    int id;
    Status status;
}

其中

public class Family extends LivingEntity {
    private House house;
    private List<Minion> members;
}

和

public class Member extends LivingEntity {
    private Family family;
    private String name;
}

所以层次图是

    BaseEntity
        |
       /|\
      / | \
     /  |  \
House Tree  LivingEntity
                |
               / \
         Family   Member

组成图是

House <---> Family ---> {Member, Member, Member, ...}
               ^           |       |       |
               |----------------------------

除了继承的内容.

房屋和树木通过其位置(在equals方法中)进行标识，因此我认为我可以将其用作@Id.我可以给他们一个特定的id字段，但这很多余.

House and Tree are identified by their location (in the equals method) so I think I can use that as the @Id. I could give them a specific id field but it's redundant.

这意味着我还需要使Point成为一个具有x和y组合ID的实体.我不知道这是否会导致同一点在数据库中被保存多次.我将保存不同的BaseEntities集，因此，如果2个在同一Point上，它将复制该Point条目还是将全部引用到一个地方?

This means that I need to make Point an entity also with a composite ID from its x and y. I don't know if this will cause the same point to be saved multiple times across the DB. I will have different sets of BaseEntities saved, so if 2 are at the same Point will it duplicate the point entry or refer all to one place?

家庭和成员由其ID定义，因为他们可以在一个房子之间移动.因此，我想在LivingEntity中使用id作为@Id，但它会与BaseEntities中的@Id发生冲突.

Family and Member are defined by their id because they can move from house to house. So I want to use id in LivingEntity as the @Id but I it will cause a conflict with the @Id from BaseEntities.

这是我的注释:

@MappedSuperclass
public abstract class BaseEntity {
    @Id
    protected Point loc;

    @OneToMany
    protected List<Property> effects = new ArrayList<>();
}

---

@Entity
@IdClass(value = PointID.class)
public class Point {
    @Id
    private int x, y;
}

class PointID {
    int x, y;
}

---

@Entity
public class Property {

    @Id
    protected int id;

    protected String name;
}

---

@Entity
public class House extends BaseEntity {
    @OneToOne
    private Family family;
}

---

@Entity
public class Tree extends BaseEntity {
    private String name;
}

---

@MappedSuperclass
public abstract class LivingEntity extends BaseEntity {
    public static enum Status { ALIVE, DECEASED }

    @Id
    int id;

    @Enumerated(EnumType.STRING)
    Status status;
}

---

@Entity
public class Family extends LivingEntity {
    @OneToOne // bidirectional? specify mappedBy?
    private House house;

    @OneToMany
    private List<Minion> members;
}

---

@Entity
public class Member extends LivingEntity {
    @ManyToOne // bidirectional? specify mappedBy?
    private Family family;

    private String name;
}

除了2个@MappedSuperclass的冲突外，我不知道我是否以正确的方式正确地使用了注释.对于这种情况，什么是好的设计?

Except for the conflict of the 2 @MappedSuperclass I don't know if I'm using the annotations correctly and in a smart way. What would be a good design for this case?

推荐答案

我不知道您的业务原因(对整个家庭而不是单个成员拥有活着"或已故"身份似乎很奇怪)，但对于给出的示例，使用类似以下内容似乎更现实:

I don't know your business reasons (it seems strange to have a an 'alive' or 'deceased' status for an entire family instead of just individual members), but for the example given, it seems more realistic to have something like:

BaseFixedObject  -> Point
        |
       /|
      / |
     /  | 
House Tree

LivingEntity  -> many Properties
        |
       /|
      / |
     /  | 
Member  | 
     Family  -> many Members


Property -> many BaseFixedObjects 

于是，财产将主要是财产的集合-带有院子的房屋，其中可能有许多树木.我不知道它是否会引用该点，或者每个树/房屋都有自己的点-这取决于您的需要.或者，您可以取消Property，让LivingEntity直接引用BaseFixedObjects.

Property would then be mostly a collection of assets on a property - A house with a yard that may have many trees. I don't know if it would reference the Point, or each tree/house has its own point - it depends on your need. Or you can do away with Property and have LivingEntity reference BaseFixedObjects directly.

这些关系可能是双向的，因此属性可以引用与其绑定的LivingEntity，该实体可以是单个成员"或家庭.我不确定在这种模式下是否需要家庭以外的共同所有权- 如果是这样，一个财产可能需要允许多个所有者，从而使其成为ManyToMany关系.

The relationships might be bidirectional, so a property may reference the LivingEntity that it is tied to, which would be a single 'member' or Family. I'm not sure if joint ownership is required outside of families in this model - if it is, a Property might need to allow more than one owner, making it a ManyToMany relationship.

这样，您的家人(可能)拥有的房屋具有固定的位置.它不需要引用点本身，因为您可以通过关联的属性对其进行访问.

This way, your family (likely) has a house that has a fixed point. It doesn't need to reference the point itself, as you have access to it through the associated properties.

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