A very strange case of DbUpdateConcurrencyException - sql-server

Question

Today I've found and an exception in my code.
DbUpdateConcurrencyException
It was very confusing because there were no changes in business logic and there was no updating of entities. After some hours of trying to understand I decided to turn on SQL Server profiler.
And here is an example of issue that I found.
Lets look at Foo entity definition:
public class Foo
{
public Foo()
{
}
public Foo(int someId, DateTime createdAt, int x, int y)
{
SomeId = someId;
CreatedAt = createdAt;
X = x;
Y = y;
}
public int SomeId { get; private set; }
public DateTime CreatedAt { get; private set; }
public int X { get; private set; }
public int Y { get; private set; }
}
If you try to add an instance of Foo and save db context it will work.
using (var myDbContext = new MyDbContext())
{
DateTime now = DateTime.UtcNow;
var foo = new Foo(1, now, 2, 2);
myDbContext.Set<Foo>().Add(foo);
myDbContext.SaveChanges();
}
Below is code that is executed when you save changes.
exec sp_executesql N'INSERT [dbo].[Foo]([SomeId], [CreatedAt], [X], [Y])
VALUES (#0, #1, #2, #3)
',N'#0 int,#1 datetime2(7),#2 int,#3 int',#0=1,#1='2015-10-15 12:45:15.2580302',#2=2,#3=2
Now lets add a computed column.
public int Sum { get; private set; }
Bellow is code for creation column in migration.
Sql("alter table dbo.Foo add Sum as (X + Y)");
Update the database. Now the code throws DbUpdateConcurrencyException. And here is why. If we look in SQL Server profiler, we'll see the code above:
exec sp_executesql N'INSERT [dbo].[Foo]([SomeId], [CreatedAt], [X], [Y])
VALUES (#0, #1, #2, #3)
SELECT [Sum]
FROM [dbo].[Foo]
WHERE ##ROWCOUNT > 0 AND [SomeId] = #0 AND [CreatedAt] = #1',N'#0 int,#1 datetime2(7),#2 int,#3 int',#0=1,#1='2015-10-15 12:55:29.4479727',#2=2,#3=2
Now the query returns [Sum] column because it is computed. Insertion works well. But result set is empty. I think it causes DbUpdateConcurrencyException. The problem is in type of #1 variable. It is datetime2(7), but if you look in type of CreatedAt column you'll see that it is datetime. If you execute the script above, you’ll find a new row with '2015-10-15 12:55:29.447' in CreatedAt column (cast works fine). But query tries to find [Sum] of the row where CreatedAt equals to '2015-10-15 12:55:29.4479727'. Of cause the result set is empty.
So, you can fix the problem in two ways:
Change the precision of column value (for example without milliseconds).
Set manually the type of CreatedAt column in migration (datetime2(7)).
In my case I select first because I don't want to change database schema.
Here is the project to reproduce the problem.
PS: Sorry for my English:)

Answer 1

facing quite a similar case I use the following extension method
public static DateTime RoundedToSeconds(this DateTime dt) {
return new DateTime(dt.Ticks - (dt.Ticks % TimeSpan.TicksPerSecond), dt.Kind);
}
then your code should be
public Foo(int someId, DateTime createdAt, int x, int y)
{
SomeId = someId;
CreatedAt = createdAt.RoundedToSeconds();
X = x;
Y = y;
}
IMHO you may use a rounding to ms.

Answer 2

This issue doesn't repro with current builds of Entity Framework Core. The parameter type for the CreatedAt becomes of type DateTime2.
I think you missed mentioning that the key of the entity contains both SomeId and CreatedAt.

Answer 3

And here is an example of issue that I found.
Lets look at Foo entity definition:
public class Foo
{
public Foo()
{
}
public Foo(int someId, DateTime createdAt, int x, int y)
{
SomeId = someId;
CreatedAt = createdAt;
X = x;
Y = y;
}
public int SomeId { get; private set; }
public DateTime CreatedAt { get; private set; }
public int X { get; private set; }
public int Y { get; private set; }
}
If you try to add an instance of Foo and save db context it will work.
using (var myDbContext = new MyDbContext())
{
DateTime now = DateTime.UtcNow;
var foo = new Foo(1, now, 2, 2);
myDbContext.Set<Foo>().Add(foo);
myDbContext.SaveChanges();
}
Below is code that is executed when you save changes.
exec sp_executesql N'INSERT [dbo].[Foo]([SomeId], [CreatedAt], [X], [Y])
VALUES (#0, #1, #2, #3)
',N'#0 int,#1 datetime2(7),#2 int,#3 int',#0=1,#1='2015-10-15 12:45:15.2580302',#2=2,#3=2
Now lets add a computed column.
public int Sum { get; private set; }
Bellow is code for creation column in migration.
Sql("alter table dbo.Foo add Sum as (X + Y)");
Update the database. Now the code throws DbUpdateConcurrencyException. And here is why. If we look in SQL Server profiler, we'll see the code above:
exec sp_executesql N'INSERT [dbo].[Foo]([SomeId], [CreatedAt], [X], [Y])
VALUES (#0, #1, #2, #3)
SELECT [Sum]
FROM [dbo].[Foo]
WHERE ##ROWCOUNT > 0 AND [SomeId] = #0 AND [CreatedAt] = #1',N'#0 int,#1 datetime2(7),#2 int,#3 int',#0=1,#1='2015-10-15 12:55:29.4479727',#2=2,#3=2
Now the query returns [Sum] column because it is computed. Insertion works well. But result set is empty. I think it causes DbUpdateConcurrencyException. The problem is in type of #1 variable. It is datetime2(7), but if you look in type of CreatedAt column you'll see that it is datetime. If you execute the script above, you’ll find a new row with '2015-10-15 12:55:29.447' in CreatedAt column (cast works fine). But query tries to find [Sum] of the row where CreatedAt equals to '2015-10-15 12:55:29.4479727'. Of cause the result set is empty.
So, you can fix the problem in two ways:
Change the precision of column value (for example without milliseconds).
Set manually the type of CreatedAt column in migration (datetime2(7)).
In my case I select first because I don't want to change database schema.
Here is the project to reproduce the problem.
PS: Sorry for my English:)