Entity Framework insert failed with date column - entity-framework

Question

I have a problems with Entity Framework (V 6.1.0), if a DateTime property is annotated as a Date type:
Column(TypeName = "Date")
public class MyTable
{
[DatabaseGenerated]
public Guid Id { get; set; }
[Key, Column(TypeName = "Date"), DataType(DataType.Date)]
public DateTime DateKey { get; set; }
[Required]
public string SomeProperty { get; set; }
}
The column of my table in SQL is created correctly as a DATE column.
Now if I try to insert a new row and set my date property e.g. with DateTime.Now() I get following error:
Store update, insert, or delete statement affected an unexpected
number of rows (0). Entities may have been modified or deleted since
entities were loaded. Refresh ObjectStateManager entries.
The problem is in the generated SQL code by EF:
exec sp_executesql N'
INSERT [dbo].[MyTable]([DateKey], [SomeProperty]) VALUES (#0, #1)
SELECT [Id] FROM [dbo].[MyTable]
WHERE ##ROWCOUNT > 0 AND [DateKey] = #0',
N'#0 datetime2(7), #1varchar(max)',
#0='2014-03-26 08:58:07',
#1='abcdef'
The parameter for DateKey is declared as DATETIME2. I think, This should be DATE.
This select statement cannot return any row, if there is any time part. If I change parameter #0 to DATE (as it is annotated in my model, I get no error even if time part is still included.
Is this a bug in EF?
Regards,
Daniel
EDIT:
I don't know if this is relevant for my question. I'm configured in OnModelCreating all my date column as DATETIME2 by default:
modelBuilder.Properties().Configure(p => p.HasColumnType("datetime2"));
EDIT on 2014-03-27
Providing a complete repro:
using System;
using System.Collections.Generic;
using System.ComponentModel.DataAnnotations;
using System.ComponentModel.DataAnnotations.Schema;
using System.Data.Entity;
using System.Linq;
using System.Text;
using System.Threading.Tasks;
namespace EFDateColumnAsKey
{
class Program
{
static void Main(string[] args)
{
MyContext ctx = new MyContext();
ctx.CalendarItems.Add(new CalendarItem() { StartDate = DateTime.Now.Date }); // This works
ctx.SaveChanges();
ctx.CalendarItems.Add(new CalendarItem() { StartDate = DateTime.Now }); // This not !!
ctx.SaveChanges();
ctx.Dispose();
}
public class MyContext : DbContext
{
public DbSet<CalendarItem> CalendarItems { get;set; }
}
public class CalendarItem
{
[DatabaseGenerated( System.ComponentModel.DataAnnotations.Schema.DatabaseGeneratedOption.Identity)]
public int Id { get; set; }
[Key, Column(Order = 1), DataType(DataType.Date)]
public DateTime StartDate { get; set; }
}
}
}

Answer 1

I have added some details to bug #2185. In summary, when we create a SqlCommand for the INSERT operation we define a parameter of type DATETIME2 for any property of type System.DateTime, but for compatibility reasons when we create the database schema by default we will create a column of type DATETIME.
The SQL we generate for the insert looks like this:
INSERT [dbo].[CalendarItems]([StartDate]) VALUES (#0);
SELECT [Id] FROM [dbo].[CalendarItems] WHERE ##ROWCOUNT > 0 AND [StartDate] = #0;
When you pass an arbitrary System.DataTime instance as a DATETIME2 parameter the least significant digits will be preserved, but as soon as the value of the DATETIME2 parameter gets stored in a DATETIME column, the value will be truncated.
Since the value stored in StartDate no longer matches the value of parameter #0, the second statement (i.e. the SELECT query we use to detect rows affected) will return zero rows and the command will fail, the transaction will get rolled back, etc.
As you already found, the possible workarounds are:
Use a surrogate identity key instead of declaring a key of type DateTime
Use DateTime2 for the column
Truncate the value in-memory before sending it to the database.
Hope this helps,
Diego