I'm attempting to create a form (Books) with a simple drop down list displaying fields from a related table (Authors).
Book Model:
namespace SimpleDropDownList.Models
{
public class Book
{
[Key]
public int BookID { get; set; }
[StringLength(255)]
[Display(Name = "Book Title")]
public string Title { get; set; }
public int AuthorID { get; set; }
public Author Author { get; set; }
public AuthorViewModel AuthorViewModel { get; set; }
}
}
Author Model:
namespace SimpleDropDownList.Models
{
public class Author
{
[Key]
public int AuthorID { get; set; }
[Display(Name = "First Name")]
[StringLength(50)]
public string FirstName { get; set; }
[Display(Name = "Last Name")]
[StringLength(50)]
public string LastName { get; set; }
public ICollection<Book> Books { get; set; } = new List<Book>();
}
}
ViewModel:
namespace SimpleDropDownList.Models
{
[NotMapped]
public class AuthorViewModel
{
//Property to hold the list of authors in the GET
public IEnumerable<SelectListItem> AuthorOptions { get; set; }
//Property to bind the selected author used in the POST
public List<int> SelectedAuthorIds { get; set; }
}
}
Create() method on the BooksController:
public IActionResult Create()
{
//ViewData["AuthorID"] = new SelectList(_context.Set<Author>(), "AuthorID", "AuthorID");
AuthorViewModel vm = new AuthorViewModel();
vm.AuthorOptions = _context.Book.Select(x => new SelectListItem()
{ Value = x.AuthorID.ToString(), Text = x.Author.LastName }).ToList();
return View(vm);
}
Create View:
@model SimpleDropDownList.Models.Book @{ ViewData["Title"] = "Create"; } <h1>Create</h1> <h4>Book</h4> <hr /> <div class="row"> <div class="col-md-4"> <form asp-action="Create"> <div asp-validation-summary="ModelOnly" class="text-danger"></div> <div class="form-group"> <label asp-for="Title" class="control-label"></label> <input asp-for="Title" class="form-control" /> <span asp-validation-for="Title" class="text-danger"></span> </div> <div class="form-group"> <label asp-for="AuthorID" class="control-label"></label> @*<select asp-for="AuthorID" class ="form-control" asp-items="ViewBag.AuthorID"></select>*@ <select asp-for="@Model.AuthorViewModel.SelectedAuthorIds" asp-items="@Model.AuthorViewModel.AuthorOptions"></select> </div> <div class="form-group"> <input type="submit" value="Create" class="btn btn-primary" /> </div> </form> </div> </div> <div> <a asp-action="Index">Back to List</a> </div> @section Scripts { @{await Html.RenderPartialAsync("_ValidationScriptsPartial");} } Model: AuthorViewModel
When the Create button is clicked the following error is generated.
An unhandled exception occurred while processing the request. InvalidOperationException: The model item passed into the ViewDataDictionary is of type 'SimpleDropDownList.Models.AuthorViewModel', but this ViewDataDictionary instance requires a model item of type 'SimpleDropDownList.Models.Book'.
My expectations are simple...open the create Book form and drop down list to display the author ID and last name.
将顶部的视图从@model SimpleDropDownList.Models.Book
更改为@model SimpleDropDownList.Models.AuthorViewModel
Now have this working. Moved the property from the Book class to the AuthorViewModel class. Now Looks like the below.
Book Model:
namespace SimpleDropDownList.Models
{
public class Book
{
[Key]
public int BookID { get; set; }
[StringLength(255)]
[Display(Name = "Book Title")]
public string Title { get; set; }
public int AuthorID { get; set; }
public Author Author { get; set; }
// Removed this link and added property to AuthorViewModel class
// public AuthorViewModel AuthorViewModel { get; set; }
}
}
Author Model:
namespace SimpleDropDownList.Models
{
public class Author
{
[Key]
public int AuthorID { get; set; }
[Display(Name = "First Name")]
[StringLength(50)]
public string FirstName { get; set; }
[Display(Name = "Last Name")]
[StringLength(50)]
public string LastName { get; set; }
public ICollection<Book> Books { get; set; } = new List<Book>();
}
}
ViewModel:
namespace SimpleDropDownList.Models
{
[NotMapped]
public class AuthorViewModel
{
//Property to hold the list of authors in the GET
public IEnumerable<SelectListItem> AuthorOptions { get; set; }
//Property to bind the selected author used in the POST
public List<int> SelectedAuthorIds { get; set; }
// Added this property to link back to Book class
public Book Book { get; set; }
}
}
Changed Create view to:
public IActionResult Create()
{
// The ViewData line auto created by the scaffolding process
// ViewData["AuthorID"] = new SelectList(_context.Set<Author>(), "AuthorID", "AuthorID");
AuthorViewModel vm = new AuthorViewModel();
vm.AuthorOptions = _context.Book.Select(x => new SelectListItem()
{ Value = x.AuthorID.ToString(), Text = x.Author.LastName }).ToList();
return View(vm);
}
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