I have a guess that the SQL EF generates is setting the field value. Even if you don't set in code, EF doesn't know that the database has a default value, and doesn't know that he should ignore it.
This article, from 2011, says that there is a DatabaseGenerated attribute, which you could use like this:
[DatabaseGenerated(DatabaseGenerationOption.Computed)]
public DateTime RegistrationDate { get; set; }
So, EF now knows that it should retrieve the data when you query the database, but should rely on the database to set the value.
However, I don't know what it would do if you explicitly set the value. Maybe it will ignore it, which may be not what you really want.
I didn't test it, it's just a guess, but it's a nice solution in my opinion.
[Edit1] Some months ago, I saw this video, and the guy does something like this in his DbContext class (i believe you have it) at 49:12 (the video is in portuguese)(i have modified the code, but didn't test it):
//This method will be called for every change you do - performance may be a concern
public override int SaveChanges()
{
//Every entity that has a particular property
foreach (var entry in ChangeTracker.Entries().Where(entry => entry.Entity.GetType().GetProperty("YourDateField") != null))
{
if (entry.State == EntityState.Added)
{
var date = entry.Property("YourDateField");
//I guess that if it's 0001-01-01 00:00:00, you want it to be DateTime.Now, right?
//Of course you may want to verify if the value really is a DateTime - but for the sake of brevity, I wont.
if (date.CurrentValue == default(DateTime))
{
date.CurrentValue = DateTime.Now;
}
else //else what?
{
//Well, you don't really want to change this. It's the value you have set. But i'll leave it so you can see that the possibilities are infinite!
}
}
if (entry.State == EntryState.Modified)
{
//If it's modified, maybe you want to do the same thing.
//It's up to you, I would verify if the field has been set (with the default value cheking)
//and if it hasn't been set, I would add this:
date.IsModified = false;
//So EF would ignore it on the update SQL statement.
}
}
}
