The enumerator obtained from SingleQueryingEnumerable is not disposed (and thus _datareader.Dispose() is not called) when an arbitrary projection (select) is enumerated:
```
System.InvalidOperationException: There is already an open DataReader associated with this Connection which must be closed first.
at Microsoft.Data.SqlClient.SqlInternalConnectionTds.ValidateConnectionForExecute(SqlCommand command)
at Microsoft.Data.SqlClient.SqlInternalTransaction.Rollback()
at Microsoft.Data.SqlClient.SqlInternalTransaction.Dispose(Boolean disposing)
at Microsoft.Data.SqlClient.SqlInternalTransaction.Dispose()
at Microsoft.Data.SqlClient.SqlTransaction.Dispose(Boolean disposing)
at System.Data.Common.DbTransaction.Dispose()
at Microsoft.EntityFrameworkCore.Storage.RelationalTransaction.Dispose()
...
```
The enumerator obtained from
SingleQueryingEnumerableis not disposed (and thus_datareader.Dispose()is not called) when an arbitrary projection (select) is enumerated:https://github.com/AutoMapper/AutoMapper.Extensions.ExpressionMapping/blob/4f66fc2bd99b94dae8b64bd2fe7653f92f8700fa/src/AutoMapper.Extensions.ExpressionMapping/Impl/SourceInjectedQueryProvider.cs#L113-L132
More info: https://stackoverflow.com/questions/4982396/does-foreach-automatically-call-dispose
This causes an exception if the underlying transaction is later committed or rolled back.
Stack trace from https://stackoverflow.com/questions/71161821/getting-odata-dto-automapper-and-unitofwork-to-play-nicely-in-aspnetboilerplate: