Linq到对象更新 [英] Linq to objects Update

问题描述

我正在使用Linq-对象，我需要进行更新.我已经环顾了一段时间，但没有真正找到任何匹配的东西.

Im using Linq - objects and I need to do an update. I've been looked around for a while but not really found anything that matches.

因此，出于参数考虑，我有2个简单的List，两个都有一个键，因此我可以愉快地使用join.

So for arguments sake I have 2 simple List's, both with a key so I can use join happily.

我找不到将结果从obj2更新为obj1的简单方法.

I cant find a simple way to update results from obj2 into obj1.

对于简单的更新，我目前正在这样做:

for simple updates I'm currently doing this:

string newValue = "something";
var items = obj1.Where(w => w.ID == iKey).Select(c => {c.<property> = newValue; return c; }).ToArray();

一切正常，花花公子. 但是，如果我将第二个表添加到混合表中，并且想用obj2替换newValue.然后我遇到了问题.

And that all works well and dandy. However if I add into the mix my second table and I want to replace newValue with obj2. then I get problems.

主要是因为我随后切换到完整的linq语句，例如:

Primarily because I then switch to a full linq statement like:

var UPDATE = from o1 in obj1
             join o2 in obj2 on o1.key equals o2.key
             select ....;

它在这里被卡住了.

如果有人可以帮助我，我将非常感激！ 预先感谢.

If anybody could help I would be extremly grateful! Thanks in advance.

推荐答案

您要在此处执行的操作与Linq并不是一件特别好的事情，因为Linq旨在查询数据而不是对其进行更新.您的Select语句依赖于副作用来执行更新.通常应避免这种情况.

What you're trying to do here isn't a particularly good thing to do with Linq as Linq is meant to be for querying data and not updating it. Your Select statement is relying on side-effects to perform the update. This generally should be avoided.

但是，您仍然可以做您想做的事.

However, you can still do what you want.

首先，我将您的查询重新排列为:

To start with, I re-arranged your query as:

var items =
    obj1
    .Where(w => w.Key == iKey)
    .Select(c => { c.Value = newValue; return c; })
    .ToArray();

然后我将其重构为:

Func<Obj, string, Obj> update =
    (c, v) => { c.Value = v; return c; };

var items = (from w in obj1
             where w.Key == iKey
             select update(w, newValue)).ToArray();

这仍然有副作用，但是我使它更加明确(希望更具可读性).

This still has the side-effect, but I made it more explicit (and hopefully more readable).

鉴于此重构，涉及两个列表的UPDATE查询变为:

Given this refactoring, the UPDATE query involving the two lists becomes:

var UPDATE = (from o1 in obj1
              join o2 in obj2 on o1.Key equals o2.Key
              select update(o1, o2.Value)).ToArray();

如果您想这样做而没有副作用，我建议您采取以下措施:

If you wanted to do this without side-effects, I would suggest the following:

var items = from w in obj1
            where w.Key == iKey
            select (Action)(() => w.Value = newValue);

Array.ForEach(items.ToArray(), a => a());

var UPDATE = from o1 in obj1
             join o2 in obj2 on o1.Key equals o2.Key
             select (Action)(() => o1.Value = o2.Value);

Array.ForEach(UPDATE.ToArray(), a => a());

您可能不喜欢这种语法，因此您可以轻松地在IEnumerable<Action>上编写快速扩展方法来调用操作，并使代码看起来像这样:

You might not like this syntax, so you could easily write quick extension method on IEnumerable<Action> to invoke the actions and would make the code look like this:

(from w in obj1
 where w.Key == iKey
 select (Action)(() => w.Value = newValue)).Invoke();

(from o1 in obj1
 join o2 in obj2 on o1.Key equals o2.Key
 select (Action)(() => o1.Value = o2.Value)).Invoke();

我希望这会有所帮助.

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