这段代码中select语句的含义是什么？ [英] What is the meaning of select statement in this code?

问题描述

List<int> obj = 
          datacontext.tblAdverts
          .Where(i => i.BusinessUserId == id)
          .GroupBy(i => i.Plans)
          .Select(i => i.Key.Value).ToList();

推荐答案

List< int> obj = datacontext.tblAdverts



//构建集合＃1：创建tblAdverts中所有条目的集合，其中条目的BusinessUserId与变量'id


。其中（i => i.BusinessUserId == id）



//构建集合＃2：分析集合＃1以构建组的集合，其中每个组（序列）包含集合＃1中的内部对象计划相同的那些项目。



.GroupBy（i => i.Plans）



//构建集合＃3：通过集合＃2中的每个组并获取Key.Value整数属性，将其添加到集合＃3



.Select（i => i.Key .Value）



//评估/渲染/处理内部Linq运算符创建的临时结构到类型列表'int



.ToList（）;

List<int> obj = datacontext.tblAdverts

// build Collection#1: create a collection of all entries in tblAdverts where the entry's BusinessUserId matches the value of the variable 'id

.Where(i => i.BusinessUserId == id)

// build Collection#2: analyze Collection#1 to build a Collection of Groups, where each Group (a sequence) contains those items in Collection#1 whose inner object 'Plans is identical.

.GroupBy(i => i.Plans)

// build Collection#3: go through each Group in Collection#2 and get the Key.Value integer property, add it to Collection#3

.Select(i => i.Key.Value)

// evaluate/render/process the temporary structures created by the internal Linq operators into a List of Type 'int

.ToList();

您是按结果分组选择的， K ey 在这里意味着你根据你所做的分组。 （此处计划），因此您选择每个组结果的 Plans.Value 属性。这里的值可能是属性，或者如果它是Nullable类型，则最可能的是 Nullable< t> .Value Property [ ^ ]

you are selecting from group by results, Key means here based on what you have done the grouping. ( here Plans), so you selecting Plans.Value property of each group results. Here value may be a property or if it is a Nullable type then most probable it is Nullable<t>.Value Property [^]

这称为LINQ（语言集成查询），借助后端将其转换为普通Sql您还可以使用名为 LINQPAD 的非常好的工具查看查询[ ^ ]

在此声明中您已提及，此查询

返回整数列表来自名为tblAdvert的表在其上下文的帮助下，即tblAdverts（通常上下文名称是复数），其中根据BusinessUserId添加过滤器并按计划列分组，然后选择键。

这一般是这个linq的意思。

但我不知道你为什么在这里使用key.Value。

我希望我能让你明白。

回复你的疑问。

谢谢。

This is called LINQ(Language Integrated Queries), with the help of which which at the back end this gets converted to normal Sql queries which you can also check using a very nice tool called LINQPAD[^]
Here in this statement you have mentioned, this query
returns a list of integers from the Table named tblAdvert with the help of its context i.e. tblAdverts(generally context names are pluralized), where a filter is added based on the BusinessUserId and Grouped by plans column and then select the key.
This iswhat in general this linq means.
But I am unaware of why you have used key.Value here.
I hope I could make you understand somehow.
Post back your queries if any.
Thanks.

这篇关于这段代码中select语句的含义是什么？的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持IT屋！