I have code like this,
IQueryable<WinnerClassExtend> dataList =
from Class in _context.AllClass
join Winner in _context.AllWinners on Class.ClassId equals Winner.ClassId
let Extend = new { Winner, Class }
group Extend by Class.ClassId into Group
select new WinnerClassExtend
{
Class = Group.Select(x => x.Class).FirstOrDefault(),
NumberOfWinnerinClass = Group.Select(x => x.Winner).Count()
};
var count = dataList.Count();
I try to get the count of IQuerable in just like what I did in .net framework and entity framework, but seems not working... And return with error "Nullable object must have a value."
I have no idea what's wrong with it, and I also try using this,
IQueryable<WinnerClassExtend> dataList =
_context.AllClass
.Join(_context.AllWinners , Class => Class.ClassId, Winner => Winner.ClassId, (Class, Winner) => new { Class, Winner })
.GroupBy(x => new { x.Class.ClassId })
.Select(x => new WinnerClassExtend
{
Class = x.Select(i => i.Class).FirstOrDefault(),
NumberOfWinnerinClass = x.Select(i => i.Winner).Count()
});
var count = dataList.Count();
And it returns the same...
I have read some issue of this error, but it seems unlike the same problem, Can anyone help?
CodePudding user response:
It seems to me that you need a left outer join:
var dataList =
from c in _context.AllClass
join w in _context.AllWinners on c.ClassId equals w.ClassId into winners
select new WinnerClassExtend
{
Class = c,
NumberOfWinnerinClass = winners.Count()
};
var count = dataList.Count();
CodePudding user response:
Try the following query:
var dataList =
from Class in _context.AllClass
select new WinnerClassExtend
{
Class = Class,
NumberOfWinnerinClass = _context.AllWinners.Where(w => w.ClassId == Class.ClassId).Count()
};
var count = dataList.Count();
Or another one:
var grouped =
from Winner in _context.AllWinners
group Winner by Class.ClassId into Group
select new
{
ClassId = Group.Key,
NumberOfWinnerinClass = Group.Count()
};
var dataList =
from Class in _context.AllClass
join g in grouped on ClassId.ClassId equals g.ClassId
select new WinnerClassExtend
{
Class = Class,
NumberOfWinnerinClass = g.NumberOfWinnerinClass
};
var count = dataList.Count();
In both cases compare execution plan.