What is the meaning of select statement in this code?

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C#

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

Posted 3-Dec-14 18:02pm

BallaviKrishna

Updated 3-Dec-14 18:38pm

Suraj Sahoo | Coding Passion

v2

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4 solutions

Solution 3

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 [^]

Posted 3-Dec-14 18:59pm

DamithSL

Solution 2

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.

Posted 3-Dec-14 18:43pm

Suraj Sahoo | Coding Passion

Solution 1

Select will return the object(List<int>) which is specified the LINQ condition.

Posted 3-Dec-14 18:40pm

Praveen Kumar Upadhyay

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BillWoodruff · Accepted Answer · 2014-12-04T03:49:00

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();