Entity Framework 6 Code First default datetime value on insert

Question

When I'm saving changes to the database, I'm running into the following exception:

Cannot insert the value NULL into column 'Registered', table
'EIT.Enterprise.KMS.dbo.LicenseEntry'; column does not allow nulls.
INSERT fails. The statement has been terminated.

The related code first model property looks like this:

[DatabaseGenerated(DatabaseGeneratedOption.Identity), DataMember]
public DateTime         Registered          { get; private set; }

... and here's why I'm confused: As far as I know, by providing the annotation [DatabaseGenerated(DatabaseGeneratedOption.Identity) I'm ordering Entity Framework to auto-generate the field (in this case: Only once at creation time.)

So I'm expecting to have a non-nullable (required) field, without the possibility to alter the field manually where EF is taking care of.

What am I doing wrong?

Notes:

I don't want to use Fluent-API, as I want to use POCOs.
The property defaultValueSql is also not an option, because I need to rely database independed for this project (e.g. for GETDATE()).
I'm using Entity Framework 6 alpha 3, Code First.

Is the AutoGenerate also your Primary key? If so, you will need to specify the [key] annotation. — Botonomous
– Botonomous, Commented Jun 11, 2013 at 15:44
I don't believe the DateTime data type has support for the identity field attribute. — marcellscarlett
– marcellscarlett, Commented Jun 11, 2013 at 20:43

Sparky · Accepted Answer · 2013-06-11 15:42:24Z

3

Try this:

[DatabaseGenerated(DatabaseGeneratedOption.Identity), DataMember]
public DateTime?            Registered          { get; private set; }

The question mark makes the property nullable

answered Jun 11, 2013 at 15:42

Sparky

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1 Comment

Atrotygma Over a year ago

I tried your solution, but it doesn't seem like it's working, though it should. Whenever I generate an migration script, the field gets marked as "nullable: false" in the script. Even on database creation. What could be wrong? The private set?

Community · Accepted Answer · 2017-05-23 12:07:38Z

2

There is no default DateTime. Only a min value.

You could potentially just set the datetime on that entity before calling dbContext.SaveChanges.

See this for a solution.

edited May 23, 2017 at 12:07

CommunityBot

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answered Jun 11, 2013 at 20:51

marcellscarlett

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Comments

Jeremy Cook · Accepted Answer · 2014-04-03 17:06:52Z

This technique behaves like a readonly field that is persisted to the database. Once the value is set it cannot (easily) be changed by using code. (Of course, you change the setter to public or internal if needed.)

When you create a new instance of a class that uses this code Registered will not initially be set. The first time the value of Registered is requested it will see that it has not been assigned one and then default to DateTime.Now. You can change this to DateTime.UTCNow if needed.

When fetching one or more entities from the database, Entity Framework will set the value of Registered, including private setters like this.

private DateTime? registered;
[Required]
public DateTime Registered
{
    get
    {
        if (registered == null)
        {
            registered = DateTime.Now;
        }
        return registered.Value;
    }
    private set { registered = value; }
}

Martin Kunc · Accepted Answer · 2019-04-12 05:40:05Z

What I did was I set value as optional and nullable. I used Data Annotation, but its also possible to use IsOptional in Fluent Api:

        [DatabaseGenerated(DatabaseGeneratedOption.Computed)]
        public DateTime? UpdatedAt { get; set; }

Then I created another Sql migration, to alter value to default:

    public partial class AlterTableUpdatedAtDefault : DbMigration
    {
        public override void Up()
        {
            Sql(@"ALTER TABLE dbo.[Table]
                  ADD CONSTRAINT DF_Table_UpdatedAt
                  DEFAULT getdate() FOR UpdatedAt");
        }

        public override void Down()
        {
            Sql(@"ALTER TABLE dbo.[Table]
                  drop CONSTRAINT DF_Table_UpdatedAt");
        }
    }

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