Is this a bug, or am I doing something wrong?

[washcroft]

The following mapping:

        [MapProperty(nameof(DataAccess.Entities.ServiceFault.ServiceFaultId), nameof(Models.ServiceFault.Id))]
        public static partial Models.ServiceFault ToModel(DataAccess.Entities.ServiceFault entity);

        [MapPropertyFromSource(nameof(Models.ServiceExtended.LastFault), Use = nameof(MapLastFault))]
        [MapProperty(nameof(DataAccess.Entities.Service.ServiceId), nameof(Models.ServiceExtended.Id))]
        public static partial Models.ServiceExtended ToModel(DataAccess.Entities.Service entity);

        public static DataAccess.Entities.ServiceFault? MapLastFault(DataAccess.Entities.Service service) =>
            service.ServiceFaults.OrderByDescending(x => x.FaultedAt).FirstOrDefault(y => y.ClearedAt != null);

...creates a Queryable expression that looks like:

[Microsoft.EntityFrameworkCore.Query.EntityQueryRootExpression]
    .Select<DataAccess.Entities.Service, Api.Models.ServiceExtended>(
        x => new Api.Models.ServiceExtended
        {
            LastFault = (x.ServiceFaults.OrderByDescending<DataAccess.Entities.ServiceFault, System.DateTime>(x => x.FaultedAt).FirstOrDefault<DataAccess.Entities.ServiceFault>(y => y.ClearedAt != null) == null)
                ? null
                : new Api.Models.ServiceFault
                {
                    Id = x.ServiceFaults.OrderByDescending<DataAccess.Entities.ServiceFault, System.DateTime>(x => x.FaultedAt).FirstOrDefault<DataAccess.Entities.ServiceFault>(y => y.ClearedAt != null).ServiceFaultId,
                    ServiceId = x.ServiceFaults.OrderByDescending<DataAccess.Entities.ServiceFault, System.DateTime>(x => x.FaultedAt).FirstOrDefault<DataAccess.Entities.ServiceFault>(y => y.ClearedAt != null).ServiceId,
                    RaisedBy = x.ServiceFaults.OrderByDescending<DataAccess.Entities.ServiceFault, System.DateTime>(x => x.FaultedAt).FirstOrDefault<DataAccess.Entities.ServiceFault>(y => y.ClearedAt != null).RaisedBy,
                    FaultedAt = x.ServiceFaults.OrderByDescending<DataAccess.Entities.ServiceFault, System.DateTime>(x => x.FaultedAt).FirstOrDefault<DataAccess.Entities.ServiceFault>(y => y.ClearedAt != null).FaultedAt,
                    ClearedAt = x.ServiceFaults.OrderByDescending<DataAccess.Entities.ServiceFault, System.DateTime>(x => x.FaultedAt).FirstOrDefault<DataAccess.Entities.ServiceFault>(y => y.ClearedAt != null).ClearedAt,
                    Reason = x.ServiceFaults.OrderByDescending<DataAccess.Entities.ServiceFault, System.DateTime>(x => x.FaultedAt).FirstOrDefault<DataAccess.Entities.ServiceFault>(y => y.ClearedAt != null).Reason
                }
        })

...which is obviously inefficient. I'm moving from AutoMapper, which uses a temporary variable to handle the same scenario.

Is there a better way to handle this in Mapperly? Thanks!

[latonz]

Thanks for reporting this. It doesn't seem optimal, and we should definitely improve it. Could you please describe how you expect the generated code to look like?
Sth. like this?

.Select(x => x.ServiceFaults.OrderByDescending(y => y.FaultedAt).FirstOrDefault(y => y.ClearedAt != null))
.Select(x => new ApiServiceExtended
{
    LastFault = x == null
        ? null
        : new ApiServiceFault
          {
              FaultedAt = x.FaultedAt,
              ClearedAt = x.ClearedAt,
              Reason = x.Reason,
              ...
           }
})

Btw, I think the generated code you provided and my sample should yield the same SQL generated by EF Core.

[latonz]

Closing as no further response was received, I'll reopen as soon as more information is provided.