通过父代对子记录进行分组，并对linq C＃求和

Question

I have a model with three properties

id int {get; set:}
name varchar {get; set:}
int fundedamount {get;set;}
list<child> childlist {get; set:}

and child like this

int id{get;set;}
int parentid{get;set;}
int amount{get;set;}

I want to group child records by parentid and sum the amount and assign it to parent.fundedamount using linq.

i am trying it like this:

 model.ForEach(f => f.childlist.Where(f1 => f1.parentid== f.Id).Sum(f2 => f2.Amount));

but how to assign it to parent.fundedamount? Do I need to use group by?

I have done without linq like this

               foreach (var f in model) {

                            foreach (var fi in f.childlist)
                            {
                                if (fi.parentid== f.Id)
                                {
                                    f.FundedAmount +=  (int)fi.Amount;
                                }
                            }  
                       }

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please suggest

Answer 1

Firstly, I group by childlist by parentId to get a collection of distinct id associated with the sum Amount .

Next, for each group in this collection, I update fundedamount corresponding with the GroupId , means Id of the model.

model.childlist.GroupBy(x=> x.parentid).Select(group => new { 
               GroupId = group.Id,
               SumOfGroup = group.Sum(x => x.Amount)
           }).ToList()
             .ForEach(group => model.First(m => m.Id = group.GroupId).fundedamount = group.SumOfGroup )

Answer 2

Why not make FundedAmount a read-only property, and have it return the sum of the Amount in the ChildList?

public int FundedAmount
{
    get { return ChildList?.Sum(c => c.Amount) ?? 0; }
}