The LINQ expression GroupByShaperExpression could not be translated

[IgorMenshikov]

At my .NET 2.2. application, I have a table named Operation mapped to a class.

It has a query:

var exportHash = (from i in context.Operation
                              where i.DeleteDate == null
                                 && exportTypeList.Contains(i.Type)
                                 && i.Status == OperationStatus.Code.Completed
                                 && i.ParentOperationID != null
                                 && operationIDList.Contains(i.ParentOperationID.Value)
                              orderby i.ProcessDate descending
                              group i by i.ParentOperationID into g
                              select new
                              {
                                  ID = g.Key,
                                  List = g.ToList()
                              }).ToDictionary(i => i.ID, i => i.List);

On 2.2 this query works but on 3.0.0-rc1, it gives an exception:

System.InvalidOperationException: 'The LINQ expression 'ToList<Operation>(GroupByShaperExpression:
KeySelector: o.ParentOperationID, 
ElementSelector:EntityShaperExpression: 
    EntityType: Operation
    ValueBufferExpression: 
        ProjectionBindingExpression: EmptyProjectionMember
    IsNullable: False
)' could not be translated. Either rewrite the query in a form that can be translated, or switch to client evaluation explicitly by inserting a call to either AsEnumerable(), AsAsyncEnumerable(), ToList(), or ToListAsync(). 

I am not sure why the grouping fails.

Operation class is quite simple:

    [Table("Operation")]
    public class Operation
    {
        [Key]
        [DatabaseGenerated(DatabaseGeneratedOption.Identity)]
        [Column("OperationID")]
        public int ID { get; set; }

        [Column("OperationTypeID")]
        public OperationType.Code Type { get; set; }

        [Column("OperationStatusID")]
        public OperationStatus.Code Status { get; set; }

        [Column]
        public int? ParentOperationID { get; set; }

        [Column]
        public DateTime? DeleteDate { get; set; }

        [Column]
        public DateTime PlanDate { get; set; }

        [Column]
        public DateTime? ProcessDate { get; set; }

        [Column]
        public int? PeriodID { get; set; }
}

Further technical details

EF Core version: 3.0.0-rc1.19456.14
Database provider: Microsoft.EntityFrameworkCore.SqlServer
Target framework: .NET Core 3.0
Operating system: Windows 10
IDE: Visual Studio 2019 16.3 Preview 4

[smitpatel]

Possibly same root cause as #17342

The GroupBy may be simple but it does not correspond to a SQL Group By. You are doing grouping.ToList(). That requires client side group by operator to generate groupings.

Duplicate of #17068

[IgorMenshikov]

You are right. Thanks for the explanation.