Fluent and Query Expression — 两者相比有什么优势吗? [英] Fluent and Query Expression — Is there any benefit(s) of one over other?

问题描述

LINQ 是自泛型以来对 .NET 的最大改进之一，它为我节省了大量时间和代码行.然而，流畅的语法对我来说似乎比查询表达式语法要自然得多.

LINQ is one of the greatest improvements to .NET since generics and it saves me tons of time, and lines of code. However, the fluent syntax seems to come much more natural to me than the query expression syntax.

var title = entries.Where(e => e.Approved)
    .OrderBy(e => e.Rating).Select(e => e.Title)
    .FirstOrDefault();

var query = (from e in entries
             where e.Approved
             orderby e.Rating
             select e.Title).FirstOrDefault();

两者之间有什么区别，或者两者之间有什么特别的好处吗?

Is there any difference between the two or is there any particular benefit of one over other?

推荐答案

两者都不是更好:它们满足不同的需求.当您想要利用多个范围变量时，查询语法就派上用场了.这发生在三种情况下:

Neither is better: they serve different needs. Query syntax comes into its own when you want to leverage multiple range variables. This happens in three situations:

• 使用 let 关键字时
• 当你有多个生成器时(from 子句)
• 进行连接时

这是一个示例(来自 LINQPad 示例):

Here's an example (from the LINQPad samples):

string[] fullNames = { "Anne Williams", "John Fred Smith", "Sue Green" };

var query =
  from fullName in fullNames
  from name in fullName.Split()
  orderby fullName, name
  select name + " came from " + fullName;

现在将其与方法语法中的相同内容进行比较:

Now compare this to the same thing in method syntax:

var query = fullNames
  .SelectMany (fName => fName.Split().Select (name => new { name, fName } ))
  .OrderBy (x => x.fName)
  .ThenBy  (x => x.name)
  .Select  (x => x.name + " came from " + x.fName);

另一方面，方法语法公开了查询运算符的全部范围，并且在简单查询时更加简洁.通过混合查询和方法语法，您可以获得两全其美.这通常在 LINQ to SQL 查询中完成:

Method syntax, on the other hand, exposes the full gamut of query operators and is more concise with simple queries. You can get the best of both worlds by mixing query and method syntax. This is often done in LINQ to SQL queries:

var query =
  from c in db.Customers
  let totalSpend = c.Purchases.Sum (p => p.Price)    // Method syntax here
  where totalSpend > 1000
  from p in c.Purchases
  select new { p.Description, totalSpend, c.Address.State };

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