Issues with Automatically setting created and modified date on each record in EF Core

Question

Using ASP.NET Core 2.2 with EF Core, I have followed various guides in trying to implement the automatic creation of date/time values when creating either a new record or editing/updating an existing one.

The current result is when i initially create a new record, the CreatedDate & UpdatedDate column will be populated with the current date/time. However first time I edit this same record, the UpdatedDate column is then given a new date/time value (as expected) BUT for some reason, EF Core is wiping out the value of the original CreatedDate which results in SQL assigning a default value.

Required result I need as follows:

Step 1: New row created, both CreatedDate & UpdatedDate column is given a date/time value (this already works) Step 2: When editing and saving an existing row, I want EF Core to update the UpdatedDate column with the updated date/time only, BUT leave the other CreatedDate column unmodified with the original creation date.

I'm using EF Core code first, and do no want to go down the fluent API route.

One of the guides i was partially following is https://www.entityframeworktutorial.net/faq/set-created-and-modified-date-in-efcore.aspx but neither this or other solutions I've tried is giving the result I am after.

Baseclass:

public class BaseEntity
{
    public DateTime? CreatedDate { get; set; }
    public DateTime? UpdatedDate { get; set; }
}

DbContext Class:

 public override Task<int> SaveChangesAsync(bool acceptAllChangesOnSuccess, CancellationToken cancellationToken = default(CancellationToken))
    {

        var entries = ChangeTracker.Entries().Where(E => E.State == EntityState.Added || E.State == EntityState.Modified).ToList();

        foreach (var entityEntry in entries)
        {
            if (entityEntry.State == EntityState.Modified)
            {
                entityEntry.Property("UpdatedDate").CurrentValue = DateTime.Now;
            }
            else if (entityEntry.State == EntityState.Added)
            {
                entityEntry.Property("CreatedDate").CurrentValue = DateTime.Now;
                entityEntry.Property("UpdatedDate").CurrentValue = DateTime.Now;
            }

        }

        return base.SaveChangesAsync(acceptAllChangesOnSuccess, cancellationToken);
    }

UPDATE FOLLOWING ADVICE FROM STEVE IN COMMENTS BELOW

I spent a bit more time debugging today, turns out the methods I posted above are appear to be functioning as expected i.e. when editing an existing row and saving it, only the entityEntry.State == EntityState.Modified IF statement is being called. So what I'm finding is that after saving the entity, the CreatedDate column is being overwitten with a Null value, I can see this by watching the SQL explorer after a refresh. I believe the issue is along the lines of what Steve mentions below "If it is #null then this might also explain the behavior in that it is not being loaded with the entity for whatever reason."

But i'm a little lost in tracing where this CreatedDate value is being dropped somewhere through edit/save process.

Image below shows the result at the point just before the entity is saved following an update. In the debugger I'm not quite sure where to find the entry of the CreatedDate to see what value is held at this step, but it appears to be missing from the debugger list so wandering whether somehow it doesn't know about the existence of this field when saving.

Below is the method I have in my form 'Edit' Razor page model class:

 public class EditModel : PageModel
{
    private readonly MyProject.Data.ApplicationDbContext _context;

    public EditModel(MyProject.Data.ApplicationDbContext context)
    {
        _context = context;
    }

    [BindProperty]
    public RuleParameters RuleParameters { get; set; }

    public async Task<IActionResult> OnGetAsync(int? id)
    {
        if (id == null)
        {
            return NotFound();
        }

        RuleParameters = await _context.RuleParameters
            .Include(r => r.SystemMapping).FirstOrDefaultAsync(m => m.ID == id);

        if (RuleParameters == null)
        {
            return NotFound();
        }
       ViewData["SystemMappingID"] = new SelectList(_context.SystemMapping, "ID", "MappingName");
        return Page();
    }

    public async Task<IActionResult> OnPostAsync()
    {
        if (!ModelState.IsValid)
        {
            return Page();
        }

        _context.Attach(RuleParameters).State = EntityState.Modified;

        try
        {
            await _context.SaveChangesAsync();
        }
        catch (DbUpdateConcurrencyException)
        {
            if (!RuleParametersExists(RuleParameters.ID))
            {
                return NotFound();
            }
            else
            {
                throw;
            }
        }

        return RedirectToPage("./Index");
    }

    private bool RuleParametersExists(int id)
    {
        return _context.RuleParameters.Any(e => e.ID == id);
    }
}

Possibly one of the reasons for this issue is the fact that I have not included the CreatedDate field in my Edit Razor Page form, so when I update the entity which in turn will run the PostAsync method server side, there is no value stored for the CreatedDate field and therefore nothing in the bag by the tine the savechangesasync method is called in my DbContext Class. But I also didn't think this was necessary? otherwise I'd struggle to see what value there is in the this process of using an inherited BaseEntity class i.e. not having to manually add the CreatedDate & UpdatedDate attribute to every model class where I want to use it...

Answer 1

Possibly one of the reasons for this issue is the fact that I have not included the CreatedDate field in my Edit Razor Page form, so when I update the entity which in turn will run the PostAsync method server side, there is no value stored for the CreatedDate field and therefore nothing in the bag by the tine the savechangesasync method is called in my DbContext Class.

That's true.Your post data does not contains the original CreatedDate,so when save to database, it is null and could not know what the exact value unless you assign it before saving.It is necessary.

You could just add below code in your razor form.

<input type="hidden" asp-for="CreatedDate" />

Update:

To overcome it in server-side,you could assign data manually:

public async Task<IActionResult> OnPostAsync()
{
    RuleParameters originalData = await _context.RuleParameters.FirstOrDefaultAsync(m => m.ID == RuleParameters.ID);

    RuleParameters.CreatedDate = originalData.CreatedDate;

    _context.Attach(RuleParameters).State = EntityState.Modified;


    await _context.SaveChangesAsync();
 }