如何建立三元关系 [英] How to model ternary relationships

问题描述

例如，三个实体：

  Bike 
 Crash 
个人
  

然后会有一个三元关系知道：

1. 哪个人在坠机X的自行车


2. 参与自行车X和Y之间的事故X的人


3. 在自行车B上遇到的人A发生什么事情

等。

我应该如何创建我的实体？
为三元关系创建新实体的唯一可能性？

解决方案

选项1

假设有 Person-Bike 组合可以不存在 Crash es（感谢上帝）。因此，假设自行车不是由特定人员拥有的，所以您可以创建具有FK对人和自行车的二进制关系（连接表） PersonBike 。 EF可以在模型中处理这种多对多的关系，而没有关联类。

然后，太糟糕了，人 - 自行车组合可能会涉及到崩溃。也许在一次崩溃中有两种以上的组合。基本上，您可以在崩溃中收集 PersonBikes 。在这种情况下，模型中就没有关联类。但是，如果您想更多地了解 Crash 和 PersonBike 之间的关联，例如谁犯了崩溃，你需要一个连接表，两者之间： CrashPersonBike 与FK到崩溃和 PersonBike 和描述关联的一个或多个字段（如有罪是/否）。这将需要EF模型中的关联类。

选项2

自行车具有特定的所有者（人）：让人有一个自行车集合（表Bike有一个FK到人） 。现在只需描述所涉及的自行车的事故就足够了，因为自行车决定了人。所以崩溃可以有一个自行车集合（再次：模型中没有关联类）或关联类 CrashBike ，其中包含如上所述的更多详细信息。

选项3

在模型中需要关联类（ CrashPersonBike ）的真实三元关系，有或没有额外的细节。

在所有情况下，您都需要业务逻辑来防止相同的人（或选项1和3中的自行车）参与一次崩溃。选项1和2还有一个额外的好处，因为该模型可以描述除了碰撞之外的人 - 自行车组合。是否应该是1或2取决于自行车人的所有权。

What's the best way to map entities to a ternary relationship with EF5?

For example, three entities:

Bike
Crash
Person

Then there would be a ternary relationship to know:

1. The bike of which person was in the crash X
2. The persons involved in the crash X between bikes X and Y
3. In what crashes were involved person A on bike B

etc.

How should I create my entities? Is the only possibility to create a new entity for the ternary relationship?

解决方案

Option 1

Suppose that there are Person-Bike combinations that can exists without Crashes (thank god). So you can create a binary relationship (junction table) PersonBike having FK's to person and bike, assuming that bikes are not owned by specific persons. EF can handle this a a many-to-many relationship without an association class in the model.

Then, too bad, Person-Bike combinations can get involved in crashes. Maybe more than two combinations in one crash. Basically you could have a collection PersonBikes in Crash. In that case there would be no association class in the model at all. But if you want to know more about the association between Crash and PersonBike, e.g. who is guilty of the crash, you need a junction table between both: CrashPersonBike with FK's to Crash and PersonBike and one or more fields describing the association (like guilty yes/no). This would require an association class in the EF model.

Option 2

Bikes have specific owners (persons): let Person have a Bikes collection (the table Bike has an FK to Person). Now it suffices to describe a crash only by the bikes that are involved, because the bikes determine the person. So Crash can have a Bikes collection (again: no association classes in the model) or an association class CrashBike that contains more details as described above.

Option 3

A "true" ternary relationship that requires an association class (CrashPersonBike) in the model, with or without extra details.

In all cases you need business logic to prevent the same persons (or bikes in option 1 and 3) from getting involved in one crash. Option 1 and 2 have an additional benefit in that the model can describe person-bike combinations apart from crashes. Whether it should be 1 or 2 depends on bike-person ownership.

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