CODEWITHSUNDEEP
c#sql-serverlinq-to-sqldatetime
ericsson007
ericsson007

Reputation: 643

Linq to SQL DateTime values are local (Kind=Unspecified) - How do I make it UTC?

Isn't there a (simple) way to tell Linq To SQL classes that a particular DateTime property should be considered as UTC (i.e. having the Kind property of the DateTime type to be Utc by default), or is there a 'clean' workaround?

The time zone on my app-server is not the same as the SQL 2005 Server (cannot change any), and none is UTC. When I persist a property of type DateTime to the dB I use the UTC value (so the value in the db column is UTC), but when I read the values back (using Linq To SQL) I get the .Kind property of the DateTime value to be 'Unspecified'.

The problem is that when I 'convert' it to UTC it is 4 hours off. This also means that when it is serialized it it ends up on the client side with a 4 hour wrong offset (since it is serialized using the UTC).

Upvotes: 62

Views: 17763

Answers (8)

aarondcoleman
aarondcoleman

Reputation: 536

For our case it was impractical to always specify the DateTimeKind as stated previously:

DateTime utcDateTime = DateTime.SpecifyKind(databaseDateTime, DateTimeKind.Utc);

We are using Entity Framework, but this should be similar to Linq-to-SQL

If you want to force all DateTime objects coming out of the database to be specified as UTC you'll need to add a T4 transform file and add additional logic for all DateTime and nullable DateTime objects such that they get initialized as DateTimeKind.Utc

I have a blog post which explains this step by step: http://www.aaroncoleman.net/post/2011/06/16/Forcing-Entity-Framework-to-mark-DateTime-fields-at-UTC.aspx

In short:

  1. Create the .tt file for your .edmx model (or .dbml for Linq-to-SQL)

  2. Open the .tt file and find the "WritePrimitiveTypeProperty" method.

  3. Replace the existing setter code. This is everything between the ReportPropertyChanging and the ReportPropertyChanged method callbacks with the following:

    <#+ if( ((PrimitiveType)primitiveProperty.TypeUsage.EdmType).PrimitiveTypeKind == PrimitiveTypeKind.DateTime)
            {
#>
        if(<#=code.FieldName(primitiveProperty)#> == new DateTime())
        {
            <#=code.FieldName(primitiveProperty)#> = StructuralObject.SetValidValue(value<#=OptionalNullableParameterForSetValidValue(primitiveProperty, code)#>);
<#+ 
            if(ef.IsNullable(primitiveProperty))
            {  
#>              
            if(value != null)
                <#=code.FieldName(primitiveProperty)#> = DateTime.SpecifyKind(<#=code.FieldName(primitiveProperty)#>.Value, DateTimeKind.Utc);
<#+             } 
            else
            {#>
            <#=code.FieldName(primitiveProperty)#> = DateTime.SpecifyKind(<#=code.FieldName(primitiveProperty)#>, DateTimeKind.Utc);                
<#+ 
            } 
#>
        }
        else
        {
            <#=code.FieldName(primitiveProperty)#> = StructuralObject.SetValidValue(value<#=OptionalNullableParameterForSetValidValue(primitiveProperty, code)#>);
        }
<#+ 
        }
        else
        {
#>
    <#=code.FieldName(primitiveProperty)#> = StructuralObject.SetValidValue(value<#=OptionalNullableParameterForSetValidValue(primitiveProperty, code)#>);
<#+ 
        }
#>

Upvotes: 5

Rob
Rob

Reputation: 11788

I use this way to specify the DateTimeKind on the fly:

DateTime myDateTime = new DateTime(((DateTime)myUtcValueFromDb).Ticks, DateTimeKind.Utc);

Upvotes: 0

Gautam Jain
Gautam Jain

Reputation: 6849

@rob263 provided an excellent method.

This is only an additional help I wish to provide if you are using Entity Framework instead of Linq To Sql.

Entity Framework does not support OnLoaded event.

Instead, you can do the following:

 public partial class Person
    {
        protected override void OnPropertyChanged(string property)
        {
            if (property == "BirthDate")
            {
                this._BirthDate= DateTime.SpecifyKind(this._BirthDate, DateTimeKind.Utc);
            }

            base.OnPropertyChanged(property);
        }

    }

Upvotes: 3

to StackOverflow
to StackOverflow

Reputation: 124706

SQL Server DateTime does not include any timezone or DateTimeKind information, therefore DateTime values retrieved from the database correctly have Kind = DateTimeKind.Unspecified.

If you want to make these times UTC, you should 'convert' them as follows:

DateTime utcDateTime = new DateTime(databaseDateTime.Ticks, DateTimeKind.Utc);

or the equivalent:

DateTime utcDateTime = DateTime.SpecifyKind(databaseDateTime, DateTimeKind.Utc);

I assume your problem is that you are attempting to convert them as follows:

DateTime utcDateTime = databaseDateTime.ToUniversalTime();

This may appear reasonable at first glance, but according to the MSDN documentation for DateTime.ToUniversalTime, when converting a DateTime whose Kind is Unspecified:

The current DateTime object is assumed to be a local time, and the conversion is performed as if Kind were Local.

This behavior is necessary for backwards compatibility with .NET 1.x, which didn't have a DateTime.Kind property.

Upvotes: 32

RobSiklos
RobSiklos

Reputation: 8849

The generated LinqToSql code provides extensibility points, so you can set values when the objects are loaded.

The key is to create a partial class which extends the generated class, and then implement the OnLoaded partial method.

For instance, let's say your class is Person, so you have a generated partial Person class in Blah.designer.cs.

Extend the partial class by creating a new class (must be in a different file), as follows:

public partial class Person {

  partial void OnLoaded() {
    this._BirthDate = DateTime.SpecifyKind(this._BirthDate, DateTimeKind.Utc);
  }
}

Upvotes: 40

Jack Ukleja
Jack Ukleja

Reputation: 13511

This code snippet will allow you to convert the DateTimes (Kind=Unspecified) you get back from LINQ to SQL into UTC times without the times being affected.

TimeZoneInfo UTCTimeZone = TimeZoneInfo.FindSystemTimeZoneById("UTC");
DateTime utcTime = TimeZoneInfo.ConvertTimeToUtc(myLinq2SQLTime, UTCTimeZone);

There are probably cleaner ways to do this but I had this to hand and could test it quickly!

I am not sure if there is a way to get it working with LINQ to SQL classes transparently - you might want to look in the partial class and see if you can hook where the values are read/written.

Upvotes: -1

Michal Rogozinski
Michal Rogozinski

Reputation: 1759

I you want UTC, TimeZone class can do it for you, if you want to convert between different timezones, than TimeZoneInfo is for you. exemple from my code with TimeZoneInfo:

TimeZoneInfo cet = TimeZoneInfo.FindSystemTimeZoneById("Central European Standard Time");
ac.add_datetime = TimeZoneInfo.ConvertTime(DateTime.Now, cet);

Upvotes: -4

Marc Gravell
Marc Gravell

Reputation: 1062855

The only way I can think to do this would be to add a shim property in a partial class that does the translation...

Upvotes: 5

Related Questions