Handlers (OnGet, OnPost)

What are Handlers?

Handlers are methods in PageModel that respond to HTTP requests (GET, POST, etc.).

OnGet Handler

Handles HTTP GET requests (displaying pages).

public class IndexModel : PageModel
{
    public List<Product> Products { get; set; } = new();

    public async Task OnGetAsync()
    {
        Products = await _context.Products.ToListAsync();
    }
}

OnPost Handler

Handles HTTP POST requests (form submissions).

public class CreateModel : PageModel
{
    [BindProperty]
    public Product Product { get; set; } = new();

    public IActionResult OnGet()
    {
        return Page();
    }

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

        _context.Products.Add(Product);
        await _context.SaveChangesAsync();

        return RedirectToPage("Index");
    }
}

Named Handlers

Handle multiple actions on the same page.

public class ProductModel : PageModel
{
    public IActionResult OnPostDelete(int id)
    {
        // Delete product
        return RedirectToPage();
    }

    public IActionResult OnPostApprove(int id)
    {
        // Approve product
        return RedirectToPage();
    }
}

<form method="post" asp-page-handler="Delete">
    <button type="submit">Delete</button>
</form>

<form method="post" asp-page-handler="Approve">
    <button type="submit">Approve</button>
</form>

Handler Parameters

// Route parameter: @page "{id:int}"
public async Task OnGetAsync(int id)
{
    Product = await _context.Products.FindAsync(id);
}

// Query parameter: ?search=laptop
public async Task OnGetAsync(string? search)
{
    var query = _context.Products.AsQueryable();
    if (!string.IsNullOrEmpty(search))
        query = query.Where(p => p.Name.Contains(search));
    
    Products = await query.ToListAsync();
}

Complete InvenTrack Example

public class EditModel : PageModel
{
    private readonly InvenTrackDbContext _context;

    public EditModel(InvenTrackDbContext context) => _context = context;

    [BindProperty]
    public Product Product { get; set; } = new();

    public async Task<IActionResult> OnGetAsync(int id)
    {
        Product = await _context.Products.FindAsync(id);
        if (Product == null)
            return NotFound();

        return Page();
    }

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

        _context.Update(Product);
        await _context.SaveChangesAsync();

        TempData["Success"] = "Product updated!";
        return RedirectToPage("Index");
    }

    public async Task<IActionResult> OnPostDeleteAsync(int id)
    {
        var product = await _context.Products.FindAsync(id);
        if (product != null)
        {
            _context.Products.Remove(product);
            await _context.SaveChangesAsync();
            TempData["Success"] = "Product deleted!";
        }

        return RedirectToPage("Index");
    }
}

Key Takeaways

• OnGet: Handles GET requests
• OnPost: Handles POST requests
• Named handlers: OnPost{Name} for multiple actions
• asp-page-handler: Specify handler in view
• Parameters: Route and query parameters
• Async: Use OnGetAsync/OnPostAsync