更改 LINQ 语句中对象的值

发布于 2025-01-03 22:22:04 字数 462 浏览 2 评论 0原文

我想向 EntityObject 添加一些计算属性，而又不失去再次查询数据库的可能性。

我创建了一个分部类并在对象中添加了我需要的字段。我编写了一个静态函数“AttachProperties”，它应该以某种方式添加一些计算值。我无法在客户端执行此操作，因为其他几个函数将一些过滤条件附加到查询中。

这些函数应该如下所示：

return query.Select(o =>
{
   o.HasCalculatedProperties = true;
   o.Value = 2;

   return o;
});

在我的例子中，计算值取决于多次查找，而不仅仅是一个简单的“2”。该示例适用于 IEnumerable，但当然不适用于 IQueryable。

我首先创建了一个新类，其中 EntityObject 作为属性，并添加了其他必要的字段，但现在我需要这个扩展类具有相同的基类型。

原文

I want to add some calculated properties to an EntityObject without loosing the possibility of querying it agains the database.

I created a partial class and added the fields I need in the object. Than I wrote a static function "AttachProperties" that should somehow add some calculated values. I cannot do this on clientside, since several other functions attach some filter-conditions to the query.

The functions should look like this:

return query.Select(o =>
{
   o.HasCalculatedProperties = true;
   o.Value = 2;

   return o;
});

In my case the calculated value depends on several lookups and is not just a simple "2". This sample works with an IEnumerable but, of course, not with an IQueryable

I first created a new class with the EntityObject as property and added the other necessary fields but now I need this extended class to be of the same basetype.

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鱼窥荷 2025-01-10 22:22:04

首先，在我看来，改变 Select() 中的对象是一个坏主意，因为它会导致其他事情发生（状态改变），而不是方法名称所暗示的（投影），这总是会带来麻烦。 Linq 植根于函数式编程（无状态）范例，因此这种用法是不可预期的。

但是您可以使用返回计算结果的方法来扩展您的类，例如：

partial class EntityObject
{
    public int GetValue()
    {
        return this.MappedProp1 * this.MappedProp2;
    }
}

从您的问题中很难判断这是否适合您。如果生成计算值涉及的不仅仅是根据对象自身属性进行简单计算，那么最好不要理会实体并创建从对象图返回计算结果的服务。

First, in my opinion changing objects in a Select() is a bad idea, because it makes something else happen (state change) than the method name suggests (projection), which is always a recipe for trouble. Linq is rooted in a functional programming (stateless) paradigm, so this kind of usage is just not expected.

But you can extend your class with methods that return a calculation result, like:

partial class EntityObject
{
    public int GetValue()
    {
        return this.MappedProp1 * this.MappedProp2;
    }
}

It is a bit hard to tell from your question whether this will work for you. If generating a calculated value involves more than a simple calculation from an object's own properties it may be better to leave your entities alone and create a services that return calculation results from an object graph.

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愚人国度 2025-01-10 22:22:04

尝试这样的操作：

return from o in collection
       select new O()
       {
           OtherProperty = o.OtherProperty,
           HasCalculatedProperties = true,
           Value = 2
       };

这将创建原始对象的副本，其中包含您所需的更改，并避免修改 select 子句中的实体带来的所有混乱。

Try something like this:

return from o in collection
       select new O()
       {
           OtherProperty = o.OtherProperty,
           HasCalculatedProperties = true,
           Value = 2
       };

This will create a copy of the original object with the changes you require and avoid all the messiness that come with modifying an entity in a select clause.

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