Razor Pages

Priority: P1 (OPERATIONAL)

ASP.NET Core Razor Pages patterns for server-rendered web applications.

Implementation Guidelines

• PageModel: Keep logic in PageModel, not in .cshtml. Use handlers (OnGet, OnPost).
• Model Binding: Use [BindProperty] for form data. [FromQuery] for query params.
• Tag Helpers: Use asp-for, asp-action, asp-route-* for type-safe HTML.
• Partial Views: Reusable UI components with <partial> tag helper.
• View Components: Complex reusable UI with server logic.
• Layout: Shared layout in _Layout.cshtml. Use sections for page-specific content.
• TempData: Flash messages with PRG (Post-Redirect-Get) pattern.

Anti-Patterns

• No logic in .cshtml: Move to PageModel or View Components.
• No ViewBag/ViewData: Use strongly-typed models.
• No inline CSS/JS: Use external files with bundling.
• No form without anti-forgery: Always include @Html.AntiForgeryToken() or use asp-antiforgery.

Code

// Pages/Users/Create.cshtml.cs
public class CreateModel(IUserService userService, ILogger<CreateModel> logger) : PageModel
{
    [BindProperty]
    public CreateUserInput Input { get; set; } = new();

    public List<SelectListItem> Roles { get; set; } = [];

    public async Task OnGetAsync()
    {
        Roles = await GetRolesAsync();
    }

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

        var result = await userService.CreateAsync(Input);

        if (!result.IsSuccess)
        {
            ModelState.AddModelError(string.Empty, result.Error!);
            Roles = await GetRolesAsync();
            return Page();
        }

        TempData["Success"] = "User created successfully";
        return RedirectToPage("./Index");
    }
}

@* Pages/Users/Create.cshtml *@
@page
@model CreateModel

<h2>Create User</h2>

@if (TempData["Error"] is string error)
{
    <div class="alert alert-danger">@error</div>
}

<form method="post">
    <div asp-validation-summary="ModelOnly" class="text-danger"></div>

    <div class="mb-3">
        <label asp-for="Input.Name" class="form-label"></label>
        <input asp-for="Input.Name" class="form-control" />
        <span asp-validation-for="Input.Name" class="text-danger"></span>
    </div>

    <div class="mb-3">
        <label asp-for="Input.Email" class="form-label"></label>
        <input asp-for="Input.Email" class="form-control" type="email" />
        <span asp-validation-for="Input.Email" class="text-danger"></span>
    </div>

    <div class="mb-3">
        <label asp-for="Input.RoleId" class="form-label"></label>
        <select asp-for="Input.RoleId" asp-items="Model.Roles" class="form-select">
            <option value="">Select a role</option>
        </select>
        <span asp-validation-for="Input.RoleId" class="text-danger"></span>
    </div>

    <button type="submit" class="btn btn-primary">Create</button>
    <a asp-page="./Index" class="btn btn-secondary">Cancel</a>
</form>

@section Scripts {
    <partial name="_ValidationScriptsPartial" />
}

Reference & Examples

For page conventions, view components, and AJAX patterns: See references/REFERENCE.md.

Related Topics

aspnet-core | blazor | security