Phần 8: Razor Pages với EF Core trong ASP.NET Core - Xử lý xung đột đồng thời (Concurrency)

[Timestamp]
public byte[] ConcurrencyToken { get; set; }

public Guid ConcurrencyToken { get; set; } = Guid.NewGuid();

modelBuilder.Entity<Department>()
    .Property(d => d.ConcurrencyToken)
    .IsConcurrencyToken();

UPDATE [Departments] SET [Name] = @p0
WHERE [DepartmentID] = @p1 AND [ConcurrencyToken] = @p2;
SELECT [ConcurrencyToken]
FROM [Departments]
WHERE @@ROWCOUNT = 1 AND [DepartmentID] = @p1;

Add-Migration RowVersion
Update-Database

dotnet ef migrations add RowVersion
dotnet ef database update

public async Task<IActionResult> OnPostAsync(int id)
{
    // Lấy entity hiện tại từ DB
    var departmentToUpdate = await _context.Departments
        .Include(i => i.Administrator)
        .FirstOrDefaultAsync(m => m.DepartmentID == id);

    if (departmentToUpdate == null)
    {
        return HandleDeletedDepartment();
    }

    // Đặt giá trị token gốc để phát hiện xung đột
    _context.Entry(departmentToUpdate)
        .Property(d => d.ConcurrencyToken)
        .OriginalValue = Department.ConcurrencyToken;

    if (await TryUpdateModelAsync<Department>(
        departmentToUpdate, "Department",
        s => s.Name, s => s.StartDate, s => s.Budget, s => s.InstructorID))
    {
        try
        {
            await _context.SaveChangesAsync();
            return RedirectToPage("./Index");
        }
        catch (DbUpdateConcurrencyException ex)
        {
            var exceptionEntry = ex.Entries.Single();
            var clientValues = (Department)exceptionEntry.Entity;
            var databaseEntry = exceptionEntry.GetDatabaseValues();
            
            if (databaseEntry == null)
            {
                ModelState.AddModelError(string.Empty, 
                    "Unable to save. The department was deleted by another user.");
                return Page();
            }

            var dbValues = (Department)databaseEntry.ToObject();
            await SetDbErrorMessage(dbValues, clientValues, _context);

            // Cập nhật token với giá trị database hiện tại
            Department.ConcurrencyToken = dbValues.ConcurrencyToken;
            ModelState.Remove($"{nameof(Department)}.{nameof(Department.ConcurrencyToken)}");
        }
    }

    return Page();
}

@page "{id:int}"
<form method="post">
    <input type="hidden" asp-for="Department.DepartmentID" />
    <input type="hidden" asp-for="Department.ConcurrencyToken" />
    
    <!-- Các trường form khác -->
    
    <input type="submit" value="Save" class="btn btn-primary" />
</form>

private async Task SetDbErrorMessage(Department dbValues,
    Department clientValues, SchoolContext context)
{
    if (dbValues.Name != clientValues.Name)
    {
        ModelState.AddModelError("Department.Name",
            $"Current value: {dbValues.Name}");
    }
    if (dbValues.Budget != clientValues.Budget)
    {
        ModelState.AddModelError("Department.Budget",
            $"Current value: {dbValues.Budget:c}");
    }
    
    ModelState.AddModelError(string.Empty,
        "The record you attempted to edit was modified by another user. " +
        "The current values have been displayed. " +
        "If you still want to edit, click Save again.");
}

public async Task<IActionResult> OnPostAsync(int id)
{
    try
    {
        if (await _context.Departments.AnyAsync(m => m.DepartmentID == id))
        {
            _context.Departments.Remove(Department);
            await _context.SaveChangesAsync();
        }
        return RedirectToPage("./Index");
    }
    catch (DbUpdateConcurrencyException)
    {
        return RedirectToPage("./Delete",
            new { concurrencyError = true, id = id });
    }
}

@page "{id:int}"
<form method="post">
    <input type="hidden" asp-for="Department.DepartmentID" />
    <input type="hidden" asp-for="Department.ConcurrencyToken" />
    <input type="submit" value="Delete" class="btn btn-danger" />
</form>