how to get unique id from radiobuttonfor in mvc

Question

I have a below model

public class category
{
    [Key]
    public long category_id { get; set; }
    public string category_desc { get; set; }
    public long? client_id { get; set; }
    public long? display_sno { get; set; }
}

controller passing the model to view

public ActionResult category(long? client_id)
{
    var category_type = db.category.Where(m => m.client_id == null).ToList();
    if(client_id == 10)
    {
        category_type = db.category.Where(m => m.client_id == client_id).ToList();
    }
    return View(category_type);
}

In view populating the radion button

@foreach (var item in Model)                                                 
{ 
    @Html.DisplayFor(modelItem => item.display_sno)<text>.</text> &nbsp;
    @Html.RadioButtonFor(modelItem => item.category_id, item.category_id, new { id=item.category_id})@item.category_desc
}

post Method

public ActionResult Category(category g)
{

}

In post method g is coming as null. What I am missing here?

Answer 1

Your misunderstanding how radio buttons work. They are for binding one of many options to a single property, in the same way a dropdownlist works. Your code is generating radio buttons that bind to itself. And if you inspect the html you will see that it generates name="item.category_id" which would not bind to your model anyway (that would only bind to a model containing a complex object named Item which contained a property named category_id).

Assuming you have a model for a Product which contained a property for its Category, and you wanted to assign one of the values of your category table to the Category property, then your view models would look like

public class ProductVM
{
    [Required(ErrorMessage = "Please select a category")]
    public int? Category { get; set; }
    public IEnumerable<CategoryVM> CategoryOptions { get; set; }
}

public class CategoryVM
{
    public int ID { get; set; }
    public string Name { get; set; }
}

Note the use of a nullable property for Category is explained in What does it mean for a property to be [Required] and nullable?

Then the controller methods (for a Create view) would look like

public ActionResult Create()
{
    ProductVM model = new ProductVM();
    ConfigureViewModel(model);
    return View(model);
}
public ActionResult Create(ProductVM model)
{
    if (!ModelState.IsValid())
    {
        ConfigureViewModel(model);
        return View(model);
    }
    .... // Initialize your Product data model, set its properties based on the view model
    // Save and redirect
}
private void ConfigureViewModel(ProductVM model)
{
    model.CategoryOptions = db.categories.Select(x => new CategoryVM
    {
        ID = x.category_id,
        Name = x.category_desc
    });
}

Then the view would be

@model ProductVM
....
@using (Html.BeginForm())
{
    @Html.DisplayNameFor(m => m.Category)
    foreach(var category in Model.CategoryOptions)
    {
        <label>
            @Html.RadioButtonFor(m => m.Category, category.ID, new { id = "" })
            <span>@category.Name</span>
        </label>
    }
    @Html.ValidationMessageFor(m => m.Category)
    <input type="submit" .... />
}

Note that the new { id = "" } is removing the id attribute which would otherwise be invalid html because of duplicates.