EF Code First ApplicationUser required DateTime not added - asp.net-core

Question

I have a problem registering new users with my new ASP.NET Core Application (Code First).
When registering i'm using an `ApplicationUser` inheriting from `IdentityUser`.
public class ApplicationUser : IdentityUser
{
[Required]
[DefaultValue(5)]
public int ViewerRange { get; set; }
[DefaultValue(false)]
[Required]
public bool IsTACAccepted { get; set; }
public DateTime? TACAccepted { get; set; }
[Required]
[DatabaseGenerated(DatabaseGeneratedOption.Identity)]
public DateTime Created { get; set; }
[Required]
[DatabaseGenerated(DatabaseGeneratedOption.Computed)]
public DateTime Modified { get; set; }
public string Role { get; set; }
public ApplicationUser()
{
Modified = DateTime.Now;
Created = DateTime.Now;
}
}
Here´s the part of Register.cshtml.cs
public async Task<IActionResult> OnPostAsync(string returnUrl = null)
{
returnUrl ??= Url.Content("~/");
ExternalLogins = (await _signInManager.GetExternalAuthenticationSchemesAsync()).ToList();
if (ModelState.IsValid)
{
var user = new ApplicationUser
{
UserName = Input.Email,
Email = Input.Email,
Role = Input.Role,
Created = DateTime.Now,
Modified = DateTime.Now,
IsTACAccepted = false,
ViewerRange = 5
};
var result = await _userManager.CreateAsync(user, Input.Password);
//[...]
When registering, the CreateAsync Method fails with the following error:
InvalidOperationException: The value for property 'ApplicationUser.Modified' cannot be set to null because its type is 'System.DateTime' which is not a nullable type.
I can't understand why this is failing.
Can someone explain in detail please?
Kind regards

Answer 1

The reason for the error is that [DatabaseGenerated(DatabaseGeneratedOption.Computed)] says its value is generated by the database, so any assigned value should be ignored. The error shows this isn't the case though.
This isn't the only oddity in the code. [DatabaseGenerated(DatabaseGeneratedOption.Identity)] on a DateTime makes no sense. IDENTITY is used to autoincrement numeric fields. This has no meaning for a DateTime column.
f you want to specify the values yourself, remove the DatabaseGenerated attributes and use them as normal fields. You can avoid the explicit assignment by specifying a default property value, eg
public DateTime Created { get; set; } = DateTime.Now;
public DateTime Modified { get; set; } = DateTime.Now;
It's also possible to configure the database to generate those values. This is described in the docs, in the Generated Values article. Adding Created and Modified columns is described in the Date/time generation section.
A default value constraint for the Created column can be specified with HasDefaultValueSql :
protected override void OnModelCreating(ModelBuilder modelBuilder)
{
modelBuilder.Entity<Blog>()
.Property(b => b.Created)
.HasDefaultValueSql("getdate()");
}
The Modified timestamp needs a trigger though, which can't be specified in a DbContext's model. This must be created in the database, either directly :
CREATE TRIGGER [dbo].[Blogs_UPDATE] ON [dbo].[Blogs]
AFTER UPDATE
AS
BEGIN
SET NOCOUNT ON;
IF ((SELECT TRIGGER_NESTLEVEL()) > 1) RETURN;
DECLARE #Id INT
SELECT #Id = INSERTED.BlogId
FROM INSERTED
UPDATE dbo.Blogs
SET LastUpdated = GETDATE()
WHERE BlogId = #Id
END
Or through a raw SQL migration that executes the same script :
migrationBuilder.Sql(
#"
EXEC ('CREATE TRIGGER [dbo].[Blogs_UPDATE] ON [dbo].[Blogs]
AFTER UPDATE
AS
BEGIN
SET NOCOUNT ON;
IF ((SELECT TRIGGER_NESTLEVEL()) > 1) RETURN;
DECLARE #Id INT
SELECT #Id = INSERTED.BlogId
FROM INSERTED
UPDATE dbo.Blogs
SET LastUpdated = GETDATE()
WHERE BlogId = #Id
END')");

Answer 2

public DateTime? Created { get; set; }
public DateTime? Modified { get; set; }
Use this, your model needs to be told that there can be null values inside your database, otherwise it will assume there aren't.
UPDATE
**I did not actually carefully noticed your error. Now I will update my answer:-**
I see you did not use this property in your controller. so initially this property nullable. for that you found this issue. first of all, use this property to ignore nullable.
Try like this:-
public DateTime TACAccepted { get; set; } = DateTime.Now;
You can try this because your property it's null. You set this property like the above code for ignoring the nullable. or you remove this property from your model if it's don't need. I think it's will resolve your issue.
Also, make sure that column is declared as a DateTime in your SQL Database.