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

Question

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 t

Answer 1

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

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

Answer 2

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.

Answer 3

@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);
        }

    }

Answer 4

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

Answer 5

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.

Answer 6

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)#>);
<#+ 
        }
#>