CODEWITHSUNDEEP
c#sqllinqt-sqllinq-to-sql
Adventurer
Adventurer

Reputation: 73

How this query works?

So, i have a piece of code

var _activeContract = (from cnt in UnitOfWork.Context.Contract.Where(w => w.IS_DELETED == 0 && w.CONTRACT_STATUS_ID == (int)NemsKysContractStatusEnum.Aktif)
    join sei in UnitOfWork.Context.SiteExtendedInfoList.Where(w => w.IS_DELETED == 0) on cnt.SITE_ID equals sei.SITE_ID
    join sr in UnitOfWork.Context.Subregion.Where(w => w.IS_DELETED == 0) on sei.RN_SUBREGION_ID equals sr.ID
    join r in UnitOfWork.Context.Region.Where(w => w.IS_DELETED == 0) on sr.REGION_ID equals r.ID
    join mr in UnitOfWork.Context.MainRegion.Where(w => w.IS_DELETED == 0) on r.MAIN_REGION_ID equals mr.ID
    select new { MRNAME = mr.NAME, cnt.ID }).GroupBy(g => g.MRNAME).OrderBy(t => t.Key).Select(s => new { name = s.Key, data = s.Count() }).ToList();

I can't understand the last line.

As I know it says to create the output sequence, each element of it is
{ MRNAME = mr.NAME, cnt.ID } i.e. anon object. Then we group this sequence by MRNAME and then we order it by Key (part OrderBy(t=>t.Key)). What Key? Where is this key from? Because we just have two fields: MRNAME and cntID, don't we?

Then I can't understand how
Select(s => new { name = s.Key, data = s.Count() }) works. It creates on each element of previous sequence of { MRNAME = mr.NAME, cnt.ID } objects a new sequence each element of that is an object like { name = s.Key, data = s.Count() }.

Again i don't understand what Key is here and what we count calculate field data by s.Count(), what we count exactly?

Upvotes: 0

Views: 76

Answers (1)

Amy B
Amy B

Reputation: 110081

  from ...
  select new { MRNAME = mr.NAME, cnt.ID })  //1
.GroupBy(g => g.MRNAME)  //2
.OrderBy(t => t.Key)  //3
.Select(s => new { name = s.Key, data = s.Count() })  //4
.ToList();

Each element of the output from GroupBy is an IGrouping, which has a Key property.

Reading the code call by call:

//1 Each element has MRName and ID properties.
//2 Group the elements by the MRName property, we now have a query consisting of groups.
//3 Order the groups by the Key, which is the MRName property.
//4 Turn each group into a new element.  Each element has a name and data property.

Upvotes: 1

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