ProjectTo doesn't work with EF Core 3 and GroupBy

[MihaMarkic]

Source/destination types

// Entity
public class Party {
  public int Id { get; set; }
  public string Name { get; set; }
  public byte[] RowVersion { get; set; } // timestamp type in SQL Server
}

// Model is the same
public class PartyEditModel {
  public int Id { get; set; }
  public string Name { get; set; }
  public byte[] RowVersion { get; set; }
}

Mapping configuration

CreateMap<Party, PartyEditModel>();

Version: x.y.z

Automapper 9.0.0
EF Core 3.0.0

Expected behavior

db.Party.ProjectTo<PartyEditModel>(mapper.ConfigurationProvider).GroupBy(p => p.LastName).Select(g => new { g.Key, count = g.Count() }).ToArray();

Should group normally.

Actual behavior

An exception is thrown
System.InvalidCastException: 'Unable to cast object of type 'Microsoft.EntityFrameworkCore.Query.SqlExpressions.ColumnExpression' to type 'System.Linq.Expressions.ConstantExpression'.'

Steps to reproduce

Run this statement

`db.Party.ProjectTo<PartyEditModel>(mapper.ConfigurationProvider).GroupBy(p => p.LastName).Select(g => new { g.Key, count = g.Count() }).ToArray();`

Note that byte[] mapping is causing problems. When removed on model, the grouping works.

[lbargaoanu]

ProjectTo should be the last call in the chain.

[MihaMarkic]

@lbargaoanu Nope, why would it? EF Core can deal with projections as long as they are executed on serer side. And again, the problem is mapping of byte[] property (RowVersion in my sample) only, not with projections in general.

[lbargaoanu]

If it can deal with them, then just forget about AM and simply write that query using LINQ. Check the execution plan.

[MihaMarkic]

So, instead of fixing what seems to be a bug, you are proposing to ditch AM instead?

[lbargaoanu]

No, I'm explaining how to remove AM from the equation.

[MihaMarkic]

Sorry, I don't follow. Why would I remove it? It's a great tool. Yet it somehow produces wrong mapping for byte array.

[jbogard]

Try mapping without AutoMapper to see if it works.

…

On Mon, Oct 21, 2019 at 3:07 PM Miha Markič ***@***.***> wrote: Sorry, I don't follow. Why would I remove it? It's a great tool. Yet it somehow produces wrong mapping for byte array. — You are receiving this because you are subscribed to this thread. Reply to this email directly, view it on GitHub <#3245?email_source=notifications&email_token=AAAZQMXVJLOI2SFJPG5FRILQPYDYJA5CNFSM4JC7LFN2YY3PNVWWK3TUL52HS4DFVREXG43VMVBW63LNMVXHJKTDN5WW2ZLOORPWSZGOEB3T2PA#issuecomment-544685372>, or unsubscribe <https://github.com/notifications/unsubscribe-auth/AAAZQMTMU2HQPXIIKSM2AXLQPYDYJANCNFSM4JC7LFNQ> .

[MihaMarkic]

If it didn't work, I wouldn't be reporting it. I'll be triple checking it, but I'm pretty confident that it works if I do a projection without AM.
I'll try comparing expressions of possible as well.

[jbogard]

That’s what you’ll need to do because EF Core has a funny habit of evaluating expressions it doesn’t understand client-side.

…

On Mon, Oct 21, 2019 at 3:41 PM Miha Markič ***@***.***> wrote: If it didn't work, I wouldn't be reporting it. I'll be triple checking it, but I'm pretty confident that it works if I do a projection without AM. I'll try comparing expressions of possible as well. — You are receiving this because you commented. Reply to this email directly, view it on GitHub <#3245?email_source=notifications&email_token=AAAZQMWPFJDK53WLCEER7T3QPYHWTA5CNFSM4JC7LFN2YY3PNVWWK3TUL52HS4DFVREXG43VMVBW63LNMVXHJKTDN5WW2ZLOORPWSZGOEB3XB7Y#issuecomment-544698623>, or unsubscribe <https://github.com/notifications/unsubscribe-auth/AAAZQMVRQEQJFOSTRYYHNWLQPYHWTANCNFSM4JC7LFNQ> .

[MihaMarkic]

Guys, sorry, was my fault afterall. After digging around, it was my custom ITypeConverter<byte[], byte[]> that is causing these problems. Which I added because of another problem regarding EF row versioning, but I'll create another ticket for it.

[MihaMarkic]

I case you wonder why I went with custom type converter, here is the possible issue with EF Core and here is my stackoverflow question.

[lock]

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