NHibernate Get&字串编号 [英] NHibernate Get & string Id

问题描述

我有一个在NHibernate上分配了字符串Id的实体，当我通过ID获取实体时遇到了一个小问题.

I've an entity with assigned string Id on NHibernate and I've a little problem when get an entity by Id.

示例...

假设有这样的数据库记录...

Suppose that have a database record like this...

Id    Description
-------------------
AAA   MyDescription

现在，如果我使用搜索ID为"aaa"的获取"方法...

now, if I use "Get" method using search id "aaa"...

MYENTITYTYPE entity = Session.Get<MYENTITYTYPE>("aaa")

返回权实体，但ID字段(entity.Id)为"aaa"，但我希望它等于"AAA".

return right entity but Id field (entity.Id) is "aaa", while I wish it were equal to "AAA".

总而言之，我希望"Get"方法返回与数据库中存储的ID相同的ID ...大小写相同.

In summary I would like that "Get" method return the id identical to the one stored in the database...with the same case.

可能吗?我该怎么办?

推荐答案

有趣的问题.我的猜测是不可能，因为该ID可能在数据库调用之前之前存在.请考虑以下内容:

Interesting question. My guess is that it's not possible, because the Id might exist before the DB call. Consider the following:

var foo = session.Load<Foo>("aaa"); //no DB call, foo is a proxy
Console.WriteLine(foo.Id); //Prints "aaa";
var bar = foo.Bar; //Forces loading
Console.WriteLine(foo.Id); //No matter what, the Id can't change at this point

这说明了具有含义的主键通常是个坏主意的另一个原因，尤其是在其输入不受控制的情况下.

This illustrates another reason why primary keys with meaning are usually a bad idea, especially if their input is not controlled.

现在，如果您使用查询而不是Get，则会获得右写的ID:

Now, if instead of Get you use a query, you will get the right-cased Id:

//example with LINQ; you can use HQL, Criteria, etc
var foo = session.Query<Foo>().Single(x => x.Id == "aaa");

缺点是，即使实体已经加载，您也将始终访问数据库.

The drawback is that you will always go to the DB, even if the entity is already loaded.

现在，如果您将实体定义为 {Id，代码，描述} ，其中Id是合成POID(我建议 Hilo 或 Guid )，而Code是现有的字符串ID，则可以避免由于使用Get而不是使用代码查询而引起的潜在错误.

Now, if you defined your entity as {Id, Code, Description}, where Id is a synthetic POID (I recommend Hilo or Guid) and Code is the existing string Id, you will avoid potential bugs caused by using Get instead of a query with the code.

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