如何与具有两个以上关系的实体建立逆关系? [英] How to build inverse relationship to Entity which has more than two relationship to it?

问题描述

我有一个具有关系的实体Group和Person:

I have an entities Group and Person with relationships:

Group:

Group.leader ->  Person (To One)
Group.looser ->  Person (To One)
Group.others ->> Person (To Many)

在 leader ， looser 和 others 集中，我可以有不同的 Person 实体.同一个人可能在一组中是 leader ，在第二组中是 loser ，并在第三组中的 others 中出现.

In leader, looser and others set I could have different Person entities. Same Person could be leader in one group, looser in second and appears in others set in third group.

我有一对多关系 groups 应该连接

in Person entity I have To-Many relationship groups which should connect

Person:

Person.groups ->> Group (should be enough but warnings)

因为我只能建立一个逆向关系会发出警告"某些东西应该具有相反的含义"

Because I can make only one inverse relationship I always will have a warning "something should have inverse"

如何处理这样的关系?

或:我有实体 Cube ， Plan 和 Line . Cube 具有以下关系: x ， y ， z ，飞机 x 和y ，仅按 x 行.而且我需要在它们之间共享一些价值，甚至有时是混杂的:

Or: I have entities Cube, Plan and Line. Cube has relationships x, y, z, Plane x and y, Line just x. And I need to share some values between them, even sometimes mixed:

Cube:
Cube.x --> Value
Cube.y --> Value
Cube.z --> Value

Plane:
Cube.x --> Value
Cube.y --> Value

Line:
Cube.x --> Value

Value:
Value.counted -->> Line.x or Line.y, Plane.x, Cube.x, y, z, SomeAnotherEntity.neededValue

推荐答案

Apple建议每个关系都应具有逆关系.在您的情况下，这意味着 Person 实体将具有三个关系:

Apple recommend that every relationship should have an inverse. In your case, that would mean the Person entity would have three relationships:

Person.groupsLed ->> Group (to many) // "groups where this Person is leader"
Person.groupsLost ->> Group (to many) // "groups where this person is the looser"
Person.otherGroups ->> Group (to many) // "other groups with this person as a member"

这看起来确实很复杂.一种替代方法是使用中间实体(?)将三个关系折叠为一个(针对 Person 和 Group 中的每一个):

which does seem rather complicated. One alternative would be to collapse the three relationships into one (for each of Person and Group) with an intermediate entity (Ranking?):

Group.rankings ->> Ranking (to many) // "the ranking of people for this group"
Person.rankings ->> Ranking (to many) // "the ranking of this person in different groups"

在每种情况下，倒数都是一:

In each case the inverse would be to-one:

Ranking.person -> (Person) (to one) // "the person for this ranking"
Ranking.group -> (Group) (to one) // "the group for this ranking"

然后，您可以将属性添加到 Ranking 实体，以指示领导者/放松者/其他人.那可能是一个简单的字符串属性 rank ，它使用值"leader"，"loser"或"other"或等效的整数枚举.要管理 Group 和 Person 之间的关系，可以添加或删除 Ranking 对象.所有这一切的一个缺点是，找到领导者或宽松者需要对排名进行过滤，但这确实给了您一定的灵活性.

You can then add an attribute to the Ranking entity to indicate the leaders/loosers/other. That could be a simple string attribute rank which takes the values "leader", "looser" or "other", or an equivalent integer enum. To manage the relationship between a Group and a Person, you add or remove Ranking objects. One downside to all this is that finding the leader or looser involves filtering the rankings, but it does give you a degree of flexibility.

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