存储没有显式 ID 的简单关系
所以，我有两个表，分别称为“用户”和“项目”。我希望每个用户都能够标记（就像“盯着”Google 宇宙中的东西）任何项目。
现在，从集合论的角度来看，将其存储为用户和项目之间的简单关系应该是合理的。将此新表命名为 UserItemFlags。该表应该有两列；一个具有 User 表的外键，另一个具有 Item 表的外键。如果用户 U 标记了项目 I，则这由 UserItemFlags 表中存在的行 (U, I) 表示。
现在，我在 Fluent-NHibernate 中表达这一点的问题是：我似乎无法理解如何处理 Id 映射。理想情况下，我不会有 ID，因为除了用户和项目之间存在或不存在这种关系之外，没有什么其他的了。该模型的一个自然结果是表中不可能有重复的行。这是一个理想的功能。
using FluentNHibernate.Mapping;
public class UserItemFlagsMapping : ClassMap<UserItemFlags>
{
public UserItemFlagsMapping()
{
// Aaaa! I must have an Id!
References(x => x.User).Not.Nullable();
References(x => x.Item).Not.Nullable();
}
}
我很高兴收到任何正确方向的指示，即使他们会要求我在这个特定情况下放弃 Fluent。
So, I have two tables, call them User and Item. I want each user to be able to flag (like "staring" things in the Google universe) any item.
Now, from a set-theoretic perspective it should be reasonable to store this as a simple relation between users and items. Call this new table UserItemFlags. The table should have two columns; one with foreign keys to the User table, the other with foreign keys to the Item table. If user U flags item I, this is then represented by the presence of the row (U, I) in the UserItemFlags table.
Now, my problem with expressing this in Fluent-NHibernate is this: I can't seem to understand what to do with the Id mapping. Ideally, I would have no ID, because there is nothing more to it than presence or absence of this relation between a User and an Item. A natural consequence of this model is that it's impossible to have duplicate rows in the table. This is a desired feature.
using FluentNHibernate.Mapping;
public class UserItemFlagsMapping : ClassMap<UserItemFlags>
{
public UserItemFlagsMapping()
{
// Aaaa! I must have an Id!
References(x => x.User).Not.Nullable();
References(x => x.Item).Not.Nullable();
}
}
I'd be happy for any pointers in the right direction, even if they would require me to abandon Fluent for this specific case.
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评论（2）
你说你没有身份证是什么意思？您有一个由用户 ID 和项目 ID 组成的复合 ID。
编辑：答案就在这条评论中：
What do you mean you don't have an ID? You have a composite ID right there of both user ID and item ID.
Edit: The answer is in this comment:
我还没有使用 Fluent NHibernate，但使用标准 NHibernate 通常我不会像这样直接映射表。
多对多表只是在关系的两侧创建为集合。
所以你将拥有：
将元素添加到集合中将在映射表 UserItemFlags 内创建行。
参见：
http://marekblotny.blogspot.com/2009/02/fluence -nhbernate-and-collections.html
大卫
I don't have used yet Fluent NHibernate but with standard NHibernate usually I don't directly map table like this.
Many-to-many tables are just created as collection on the two side of the relationship.
So you will have:
Adding element to the collection will create rows inside the mapping table UserItemFlags.
See also:
http://marekblotny.blogspot.com/2009/02/fluent-nhbernate-and-collections.html
Davide