EF Core 3.1: Group by Sum - linq

Question

Let's suppose I have a list of player scores that looks somewhat like this:
public class ScoreEntry
{
public int PlayerId {get; set;}
public int Score {get; set;}
public string SomeOtherValue {get;set;}
}
And there are multiple entries for a single player, so I want to group those score entries and sum up their score values, something like this:
var query =
from entry in scores
group entry by entry.PlayerId into scoreEntryGroup
select new ScoreEntry()
{
PlayerId = scoreEntryGroup.Key,
Amount = scoreEntryGroup.Sum(g => g.Score),
SomeOtherValue = scoreEntryGroup.FirstOrDefault().SomeOtherValue
};
It throws an exception and I know that the problem is that I can't use SingleOrDefault() and many other similar methods in a group in EF Core 3.1
Could you help me find another way to achieve this? Any help would be highly appreciated!

Answer 1

Try the following query. It uses CROSS APPLY for joining to aggregation result.
var aggregations =
from entry in scores
group entry by entry.PlayerId into scoreEntryGroup
select new
{
PlayerId = scoreEntryGroup.Key,
Amount = scoreEntryGroup.Sum(g => g.Score)
};
var query =
from a in aggregations
from entry in scores
.Where(entry => entry.PlayerId == a.PlayerId)
.Take(1)
select new ScoreEntry()
{
PlayerId = entry.PlayerId,
SomeOtherValue = entry.SomeOtherValue,
Amount = a.Amount
};