Question

My table structure in sql server is :

TableId int (Pk) identity

Data string

DateNTime DateTime

---

My method is::

public int insertData(string data){

Date= DateTime.Now;

Table table= new Table();

table.Data= data;

table.DateNTime=Date;

 this.DataContext.Set<Table>().Add(table);

this.DataContext.SaveChanges();

return this.DataContext.Tables.Single(b => b.DateNTime == Date).TableId

}

The data insertion happens without any problems but in 9 out of 10 times while returning TableId I get the exception “sequence contains no elements”

Could it be that before the table row is saved the select command is fired and I get this error, if so what do I do?

Thanks
Arnab

Answer 1

SaveChanges() is a synchronous “blocking” operation, it doesn’t return before the transaction that saves the date is committed. So, when you call the query the date is definitely saved in the database.

I think, it is a precision/rounding problem. If you look at the precision of a DateTime in .NET you’ll see (for example in the TimeOfDay property):

TimeOfDay of .NET DateTime type: 10:32:51.0312500

So, the precision is 10E-7 seconds. A datetime in SQL Server has only 10E-3 seconds precision and the .NET DateTime is saved like this in the database:

Column value of SQL Server datetime type: 10:32:51.030

So, it is rounded to three digits. When you run the query the .NET DateTime is transmitted with high precision (as type datetime2(7) in SQL Server) …

WHERE [Extent1].[MyDateTimeColumn] = @p__linq__0',
    N'@p__linq__0 datetime2(7)', @p__linq__0='2012-05-18 10:32:51.0312500'

… and the equality comparison fails because

2012-05-18 10:32:51.0312500 != 2012-05-18 10:32:51.030

If you want a higher precision use a datetime2(7) as type in SQL Server that matches the .NET DateTime type. Or avoid such queries for equality and instead query for an interval of +/- 1 second or something around your DateTime value, like so:

var date1 = Date.AddSeconds(-1);
var date2 = Date.AddSeconds( 1);
return this.DataContext.Tables
    .Single(b => b.DateNTime >= date1 && b.DateNTime <= date2)
    .TableId;

(Not a good solution of course if you save faster than every 2nd second, Single might fail with “Sequence contains more than one element” exception.)