DbUpdateException Entries Behaves Differently When First Fails vs Others Fail

[philvmx1]

Using EF Core 6.0.8 with Pomelo 6.0.0, when we have the following:

Table - Person
| Id | Name (max 3) |

context.Add<Person>(new Person { Name = "Three" });
context.Add<Person>(new Person { Name = "A" });
context.Add<Person>(new Person { Name = "B" });
context.Add<Person>(new Person { Name = "C" });

try
{
  context.SaveChanges();
}
catch (DbUpdateException ex)
{
  ex.Entries.Count(); // 4
}

However, when we have it where the first record does not have an error:

context.Add<Person>(new Person { Name = "Three" });
context.Add<Person>(new Person { Name = "A" });
context.Add<Person>(new Person { Name = "Three" });
context.Add<Person>(new Person { Name = "B" });
context.Add<Person>(new Person { Name = "C" });

try
{
  context.SaveChanges();
}
catch (DbUpdateException ex)
{
  ex.Entries.Count(); // 1
}

Only the one record is in Entries.

We expect this to be consistent and only have the 1 Entry that failed.

The cause of this happening is the InitAsync, which is attempting to read the first result - fails and throws an exception.

MySqlConnector/src/MySqlConnector/MySqlDataReader.cs

Line 482 in dd518bf

await m_resultSet.ReadResultSetHeaderAsync(ioBehavior).ConfigureAwait(false);

That exception is caught and EF Core selects all Entries whereas in ConsumeAsync, it only selects the current command Entry.

https://github.com/dotnet/efcore/blob/42e6cfbd0c5b431a89b1923e7b73296705cf7ddf/src/EFCore.Relational/Update/ReaderModificationCommandBatch.cs#L383

ExecuteReaderAsync should return a reader, but perhaps shouldn't read anything. Not sure what other implementations are doing though.

[philvmx1]

After further investigation, I think this is more about EF Core. Submitted issue there: dotnet/efcore#33098

Seems that the ODIC provider does the same as MySqlConnector. There's a comment in that code so it seems to be the intent.

[bgrainger]

This seems like a Pomelo or EF Core issue; please reopen if there's specific behaviour in MySqlConnector (that can be reproduced just with ADO.NET) that needs to be changed.

[philvmx1]

agreed, this is an ef core issue I opened the issue there.