C# Linq GroupBy ==> Class vs Anonymous class --- different result

Question

I have the following code:

var rawGroupBEFORE = sqlRaw.GroupBy(x => new
{
    x.ID,
    x.P1,
    x.P2,
    x.P3,
    x.P4,
    x.P5,
    x.P6,
    x.P7,
    x.P8,              
}).ToList();

var rawGroup = sqlRaw.GroupBy(x => new RawDocument
{
    Id = x.ID,
    P1 = x.P1,
    P2 = x.P2,
    P3 = x.P3,
    P4 = x.P4,
    P5 = x.P5,
    P6 = x.P6,
    P7 = x.P7,
    P8 = x.P8,              
}).ToList();

And with the data that I have in the rawGroupBEFORE 1 element as result. In the rawGroup gives me 2 elements ..... wrong grouping. I have created the class RawDocument using the automatic Visual Studio "create missing property" action.

Any ideas why I should be getting this behavior?

You are running one query after another. Are results also different if you run just one (comment either first)? Ideally you need present a proof of the problem in a form of [mcve]. — Sinatr, Nov 12 '20 at 10:06
@Sinatr the result is always the same if I comment or not..... or if I invert them. Its is always the same. — Dryadwoods, Nov 12 '20 at 10:07
@SvyatoslavDanyliv No... the class is a plain DTO object with just properties like: public int Id { get; set; } — Dryadwoods, Nov 12 '20 at 10:08
which net version is it? is the variable sqlraw already fetched data (with a tolist()) or might this be run on a sqlserver as a query? — HrkBrkkl, Nov 12 '20 at 10:22

score 9 · Accepted Answer · answered Nov 12 '20 at 10:15

9

The most likely explanation is that the anonymous type uses value equality, while RawDocument uses reference equality. Since each item will get a new RawDocument object, none of them will be equal to each other.

Implement Equality members for RawDocument, or give the GroupBy a IEqualityComparer.

answered Nov 12 '20 at 10:15

JonasH

28,608
2
10
23

1

or in .NET 5: record types: `public record RawDocument(int Id);` or `public record RawDocument { public int Id { get; set; } }` (the latter being mutable) – Marc Gravell Nov 12 '20 at 10:20

C# Linq GroupBy ==> Class vs Anonymous class --- different result

1 Answers1