哪一个是更好的lambda表达式或

问题描述

我已经按照TblUserMessages
LINQ to SQL查询表达式

I have following LINQ to SQL query expression

from msg in TblUserMessages
join user in Aspnet_Users on msg.FromUserID equals user.UserId
select new {
       msg.FromUserID,
       msg.ToUserID,
       msg.MessageLocationID,
       msg.MessageID,
       user.UserName
       }

和下面的LINQ方法表达式：

And following LINQ method expression:

TblUserMessages
.Join (
  Aspnet_Users,
  msg => msg.FromUserID,
  user => user.UserId,
  (msg, user) =>
     new
     {
        FromUserID = msg.FromUserID,
        ToUserID = msg.ToUserID,
        MessageLocationID = msg.MessageLocationID,
        MessageID = msg.MessageID,
        UserName = user.UserName
     }
)

这两个返回相同的结果集。这是如

Both of these return same result set. Which is e.g. :

82522f05-2650-466a-a430-72e6c9fb68b7
6b2a174a-8141-43d2-b3ad-5b199bcbfcae
1
1
waheed

哪一个是更好地使用。在第一个一个或第二个之一。

Which one is better to use. The FIRST one or the SECOND one.

谢谢

推荐答案

他们是等价的。他们不只是返回的结果集相同 - 它们编译为相同的代码

They are equivalent. They don't just return the same result set - they compile to the same code.

使用查询表达式或点符号为根据可读性个别情况。对于加入，我觉得点符号相当麻烦 - 但我使用它的情况下我只有一个或两个条款（通常在哪里/选择）。即使有两个子句（通常是在那里的和的选择）我找到点符号，如果不错的话，你无论如何需要使用它。比如，我喜欢：

Use query expressions or dot notation for individual cases depending on readability. For joins, I find the dot notation quite cumbersome - but I use it for situations where I only have one or two clauses (usually where/select). Even with two clauses (usually where and select) I find dot notation nice if you then need to use it anyway. For example, I like:

var query = people.Where(person => person.Age > 18)
                  .Select(person => person.Name)
                  .Skip(100)
                  .Take(10);

在

over

var query = (from person in people
             where person.Age > 18
             select person.Name)
            .Skip(100)
            .Take(10);

有关更复杂的查询（如连接）我可能只是分隔两个：

For more complicated queries (e.g. joins) I'd probably just separate the two:

var baseQuery = from person in people
                where person.Age > 18
                join company on person.CompanyId equals company.CompanyId
                select new { person.Name, company.Name };

var fullQuery = baseQuery.Skip(100)
                         .Take(10);

我只是觉得这种分离使得它更容易阅读。

I just find this separation makes it easier to read.

我相信这是真正有用的开发人员理解什么查询表达式至少做基础 - 事实上，他们基本上翻译成点符号，而语言本身不知道什么LINQ到对象，LINQ to SQL的等;它只是下面的一个合适的模式的情况下。这是设计的一大位，这意味着查询表达式只影响语言规范的一个点点。

I believe it's really useful for developers to understand at least the basics of what query expressions do - the fact that they're basically translations into dot notation, and that the language itself doesn't know anything about LINQ to Objects, LINQ to SQL etc; it's just a case of following an appropriate pattern. It's a great bit of design, which means query expressions only affect one little bit of the language specification.

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