Clever Geek Handbook

C # LINQ select up to sum> = 0

This is a sample database table Name | Quantanity Book I | 1 Book II | 13 Book III | 5 etc...

And I want to select these lines until I have 100 words of usinq LINQ.

I have tried

.TakeWhile(x => (amount -= x.Quantanity) > 0);

But it gave me an error

"Expression tree cannot contain an assignment operator"

+3


source to share


2 answers 


int bookCount = 0;
var query = books
   .OrderBy(b => b.Quantity) // to get count 100, otherwise exceed is likely
   .AsEnumerable()
   .Select(b => {
        bookCount += b.Quantanity;
        return new { Book = b, RunningCount = bookCount  };
    })
   .TakeWhile(x => x.RunningCount <= 100)
   .Select(x => x.Book);


+5


source


Solution by type is good, but pay attention to it --- Only the part before AsEnumerable()

is executed by the data server. Basically, you pull the entire table into memory and then process it.

Let's see if we can improve this:



int bookCount = 0;

var query1 = (from b in books
         where b.Quantity > 0 && b. Quantity <= 100
         orderby b.Quantity
         select b).Take(100).AsEnumerable();


var query = query1
   .Select(b => {
        bookCount += b.Quantity;
        return new { Book = b, RunningCount = bookCount  };
    })
   .TakeWhile(x => x.RunningCount <= 100)
   .Select(x => x.Book);

This limits us to only 100 entries in memory to view up to 100.

+1


source






More articles:


All Articles