Send ViewModel via RedirectToAction ?

Question

Hi everyone,

Do you know if there is a way to send a ViewModel through a RedirectToAction method ?

Indeed I'd like to display the ViewModel errors when the ModelState is not valid inside the CreateBook method :

BookViewModel :

using System.ComponentModel.DataAnnotations;

namespace Blog.ViewModels.Home
{
    public class BookViewModel
    {
        [Required(ErrorMessage = "Please specify a name")]
        [Display(Name = "Name : ")]
        public string Name { get; set; }

        [Required(ErrorMessage = "Please specify a price")]
        [Display(Name = "Price : ")]
        public int Price { get; set; }
    }
}

Index.cshtml :

@model Blog.ViewModels.Home.BookViewModel
@{
    ViewData["Title"] = "Blog";
    Layout = "_Layout";
}

@section page_content{
    <p>Hello World form Blog !</p>

    <form novalidate asp-controller="Home" asp-action="CreateBook" method="post">
        <label asp-for="@Model.Name"></label>
        <input asp-for="@Model.Name">
        <span asp-validation-for="@Model.Name"></span>

        <label asp-for="@Model.Price"></label>
        <input asp-for="@Model.Price">
        <span asp-validation-for="@Model.Price"></span>

        <input type="submit" value="Continuer">
    </form>
}

HomeController :

using Blog.ViewModels.Home;
using Microsoft.AspNetCore.Mvc;

namespace Blog.Controllers
{
    public class HomeController : Controller
    {
        public IActionResult Index()
        {
            var bookViewModel = new BookViewModel();

            return View(bookViewModel);
        }

        [HttpPost]
        [ValidateAntiForgeryToken]
        public IActionResult CreateBook(BookViewModel bookViewModel)
        {
            if(!ModelState.IsValid)
                // When the ModelState is not valid, I'd like to redirect the user
                // to the "Index" Action with the bookViewModel to display form errors
                return RedirectToAction("Index", "Home", bookViewModel);

            // Will save the data to the DB after if ModelState is valid

            return RedirectToAction("Index", "Home");
        }
    }
}

Thanks in advance for your help

Answer 1

Hi @Bruce (SqlWork.com) , thanks for your answer.

Well I bypassed this issue by using an HttpPost version of my Index method instead, that way I can return View with the ViewModel inside.

Answer 2

A redirect causes the browser to do a get. You can pass query string parameters, but there is a max length for a query string. In general is frowned upon to pass model data via a query string. Your best option is to store the model in persistent storage, and pass a key to the model data on the query string.