Question Add Items to a WishList from 2 Separate Models

[Mitchelln11]

I'm having issues trying to make a wishlist.

I have a database with records of National Parks.
I also have a database with records of Hikers.

I have a button on the Park details view page that is supposed to redirect to an action.

@Html.ActionLink("Add Park to Wish List", "AddParkToWishList", "Hiker", new { @id = Model.ParkId }, new { @class = "btn btn-default" })

The button is passing the park Id, so I'm already getting that through the parameter.

I created a method to find the logged in user and the current park, but I'm stuck at trying to add items to my database.

public async Task<ActionResult> AddParkToWishList(int id)
        {
            string currentUser = FindRegisteredUserId(); // AspNetUser Id
            var currentHiker = _context.Hikers.Where(h => h.ApplicationId == currentUser); // Match against Hikers to find logged in user

            // Find current park
            var currentPark = _context.Parks.Where(p => p.ParkId == id).FirstOrDefault();

            HikerParkWishlistViewModel wishlist = new HikerParkWishlistViewModel()
            {
                wishlist.Hiker = currentHiker;
                // STUCK HERE. CAN'T ADD ANYTHING TO JUNCTION TABLE
            }

            await _context.SaveChangesAsync();
            return RedirectToAction("Details");
        }

I'm not sure what my Junction table is supposed to look like.
At first, I had it set up like the following, but was faced with error related to looping through a single object:

    public class HikerParkWishlist  // Junction table
    {
        [Key]
        public int HikerParkWishlistId { get; set; }

        [ForeignKey("Hiker")]
        public int HikerId { get; set; }
        public Hiker Hiker { get; set; }

        [ForeignKey("Park")]
        public int ParkId { get; set; }
        public string ParkName { get; set; }
        public Park Park { get; set; }
    }

A previous post of mine led me to believe that I should try the following:

    public class HikerParkWishlist
    {
        [Key]
        public int HikerParkWishlistId { get; set; }

        [ForeignKey("Hiker")]
        public IEnumerable<Hiker> Hiker { get; set; }

        [ForeignKey("Park")]
        public IEnumerable<Park> Parks { get; set; }
    }

Any hiker should be able to add any/all parks to their wishlist.
Any park can exist in in any/all hikers wishlists, so that should be a many-to-many relationship (correct me if that's wrong)

Where am I going wrong?

Current error:

CS1922 C# Cannot initialize type with a collection initializer because it does not implement 'System.Collections.IEnumerable'

I feel like I should be using IEnumerable, or a list on my action, but I'm not quite sure how to implement that.

 

[Skydiver]

<tongue-in-cheek>
Part of the issue here is that you are trying to do something object oriented in a relational database way. Welcome to your first experience of the object-relational impedance mismatch. Maybe you should be using an object oriented database instead of wedging objects into a relational database using an ORM like EntityFramework.
</tongue-in-cheek>

I don't use EF, but to the mighty Google, this is how you would go about configuring it to do a many-to-many relationship:

Configure Many-to-Many Relationship in Code First

Learn how to configure many-to-many relationship between entities in EF 6 code-first approach.

www.entityframeworktutorial.net

How to create a many-to-many mapping in Entity Framework?

Here is the case, I have 2 entities, such as Contract、Media。 public class Media : Entity { public string Name {get; set;} public bool Enabled *//other properties can be ignored..* } ...

stackoverflow.com

 

[Skydiver]

And a more succinct response answer in the Microsoft documentation:

Introduction to relationships - EF Core

How to configure relationships between entity types when using Entity Framework Core

docs.microsoft.com

 

[NoUserHere]

Maybe you should be using an object oriented database instead of wedging objects into a relational database using an ORM like EntityFramework.

I think I need the sick bucket!

 

[Mitchelln11]

That did it.

On my junction table:

    public class HikerParkWishlist
    {
        public int HikerId { get; set; }
        public Hiker Hiker { get; set; }

        public int ParkId { get; set; }
        public string ParkName { get; set; }
        public Park Park { get; set; }
    }

Hiker model:

public class Hiker
    {
        [Key]
        public int HikerId { get; set; }
        ...
        public List<HikerParkWishlist> Wishlists { get; set; }
    }

Park model:

    public class Park
    {
        [Key]
        public int ParkId { get; set; }
        ...
        [Display(Name = "Park Name")]
        public string ParkName { get; set; }
        public List<HikerParkWishlist> Wishlists { get; set; }
    }

The controller method:

        public async Task<ActionResult> AddParkToWishList(int id)
        {

            // Find logged in user to add to the correct wishlist
            string currentUser = FindRegisteredUserId();
            var currentHiker = _context.Hikers.Where(h => h.ApplicationId == currentUser).FirstOrDefault();

            // Find current park
            var currentPark = _context.Parks.Where(p => p.ParkId == id).FirstOrDefault();

            HikerParkWishlist wishlist = new HikerParkWishlist()
            {
                HikerId = currentHiker.HikerId,
                ParkId = currentPark.ParkId,
                ParkName = currentPark.ParkName
            };

            // make sure there are no duplicates
            bool parkExistsInWishlist = _context.HikerParkWishlists.Any(w => w.ParkId == wishlist.ParkId);
            if (parkExistsInWishlist == false)
            {
                _context.HikerParkWishlists.Add(wishlist);
                await _context.SaveChangesAsync();
            }

            return RedirectToAction("Details", "Hiker", new { id = currentHiker.HikerId });
        }

And finally the ApplicationDbContext:

        public DbSet<HikerParkWishlist> HikerParkWishlists { get; set; }

        protected override void OnModelCreating(ModelBuilder modelBuilder)
        {
            base.OnModelCreating(modelBuilder);
            modelBuilder.Entity<HikerParkWishlist>()
                .HasKey(t => new { t.HikerId, t.ParkId }); // Have to add unique id to Junction Table

            modelBuilder.Entity<HikerParkWishlist>()
                .HasOne(h => h.Hiker)
                .WithMany(l => l.Wishlists)
                .HasForeignKey(hi => hi.HikerId); // Matches HasKey

            modelBuilder.Entity<HikerParkWishlist>()
                .HasOne(p => p.Park)
                .WithMany(w => w.Wishlists)
                .HasForeignKey(pi => pi.ParkId); // Matches HasKey
        }

And that adds content to my Wishlist!

Does that look right? Or does it still look like a bastardized version of what it should be?

 

[Mitchelln11]

I recently created a method to add items to a wishlist.

I am using Park and Hiker models, and the wishlist is created to combine values from both tables.

Information is saving to the Wishlist table just fine, but I am getting an error trying to loop through each record.

Park Model:

 public class Park
    {
        [Key]
        public int ParkId { get; set; }
        [Display(Name = "Park Name")]
        public string ParkName { get; set; }
        ...
        public List<HikerParkWishlist> Wishlists { get; set; }
    }

Hiker Model:

public class Hiker
    {
        [Key]
        public int HikerId { get; set; }
        ...
        public List<HikerParkWishlist> Wishlists { get; set; }
    }

HikerPark Junction Table:

    public partial class HikerParkWishlist
    {
        public int HikerId { get; set; }
        public Hiker Hiker { get; set; }

        public int ParkId { get; set; }
        public string ParkName { get; set; }
        public Park Park { get; set; }
    }

Then in my view, I am trying to use a partial view:

<partial name="../Shared/_WishlistPartialView.cshtml" for="Wishlists" />

The ~View/Shared... method does not work for me

Partial View:

@model walkinthepark.Models.HikerParkWishlist

<h3 class="text-center">National Parks Wishlist</h3>
@foreach (var item in Model.Wishlists)
    {
        <p>@Html.DisplayFor(modelItem => item.ParkName)</p>
    }

Getting Ienumerator not set to an instance because it returns null error

 

[Mitchelln11]

-------------------------
Update:

Added a new list to allow the foreach loop to enumerate through
Updated Partial View:

@model walkinthepark.Models.HikerParkWishlist

<h3 class="text-center">National Parks Wishlist</h3>
@{
    // Create an empty list for the marker values to add into
    List<walkinthepark.Models.HikerParkWishlist> wishlist = new List<HikerParkWishlist>();
}

@foreach (var item in wishlist)
{
    HikerParkWishlist wishlistItems = HikerParkWishlist();

    wishlistItems.ParkName = item.ParkName;
    wishlist.Add(wishlistItems);

    <p>@Html.DisplayFor(modelItem => item.ParkName)</p>
}

The <h3> now displays, but the loop doesn't return anything, so that must be wrong.

 

[NoUserHere]

The code is technically the same, and so I've merged your topics for you, as there is no need to create a new topic when you're troubleshooting the same problematic code. Unless the code and the problem are completely different.

I am sorry, I don't have time at them moment to review your problem. If I find time later, tonight I will take a look.

 

[Mitchelln11]

Would the better way be View Components?