Fluent 和 Query Expression — 两者相比有什么好处吗? [英] Fluent and Query Expression — Is there any benefit(s) of one over other?

问题描述

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();

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

解决方案

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:

• When using the let keyword
• When you have multiple generators (from clauses)
• When doing joins

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;

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);

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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