LINQ to SQL执行 [英] LINQ to SQL execution

问题描述

大家好，



请看这个片段：

Hi all,

Please look at this snippet:

var query = from t in db.ThingTable
             where t.Id == id
             select t;

if (!query.Any())
    return null;

ThingTable result = _Query.First();

LINQ to SQL不是我的事，但我有一个问题。因为（在我的理解中）查询变成了一个由SQL Server执行的表达式树，所以查询将被执行两次是否有任何危险 - 一次是Any（）而一次是First（）？或者它是否足够聪明以重复使用结果集？



谢谢。

LINQ to SQL isn't really my thing, but I have a question. Because (in my understanding) the query gets turned into an expression tree to be executed by SQL Server, is there any danger that the query will get executed twice - once for the Any() and once for First()? Or is it smart enough to reuse the result set?

Thanks.

推荐答案

这将有效更快！

This will work way faster!

var foundThingTable = db.ThingTable.FirstOrDefault(tt => tt.Id == id);
return foundThingTable;

我不确定，如果重用结果集足够聪明，那就是我使用这样的querry的原因：

I am not sure, if it is enough smart to reuse the result set, that's why I am using such querry:

var query = (from t in db.ThingTable
             where t.Id == id
             select t).FirstOrDefault();
 
if (query == null)
    return null;
 
ThingTable result = query;

在这种情况下，您将只获得一条所需的记录，而无需调用First（）来获取第一条记录。

In this case you will get only one record that you need and no need to call First() to get first record.

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