Modeling a many-to-many relationship in ASP.NET MVC using LINQ to SQL

Question

I\'ve been reading and watching videos about MVC and I\'m starting to get a little confused. The simple tutorials are far too simple and they seem to only involve a single d

Answer 1

I have many examples of this type of relationship in my current project. I'm using MVC 1 and LINQ-to-SQL. I went through exactly the same frustration then as you are experiencing now. The biggest hurdle is accepting the fact that LINQ-to-SQL doesn't directly manage many-to-many relationships, but understanding that it doesn't need to in order to get the information you require.

Let's start with the R in CRUD, since it's the easiest way to demonstrate what needs to be done. Now, at this point I would recommend creating a strongly-typed view model, just to ease the task of aggregating your view data and to simplify the assignment of the meal data to the Details view:

public class MealDetailsViewModel
{
    public int Id_Meal { get; set; }
    public string Title { get; set; }
    public string Description { get; set; }

    private List _Ingredients = new List();
    public List Ingredients
    {
       get { return _Ingredients; }
       set { _Ingredients = value; }
    }
}

To retrieve a meal and its list of ingredients, here's the controller method:

public ActionResult Details (int mealID)
{
    Meal result = DataContext.Meals
        .Where(a => a.Id_Meal == mealID)
        .SingleOrDefault();

    MealDetailsViewModel viewModel = new MealDetailsViewModel
    {
        Id_Meal = result.Id,
        Title = result.Title,
        Description = result.Description,
        Ingredients = result.Meals-Ingredients
            .Where(a => a.Id_Meal == mealID)
            .Select(a => a.Ingredient)
            .ToList()
    };

    return View(viewModel);
}

As previously stated, LINQ-to-SQL doesn't directly support many-to-many relationships, which is why you cannot see the Ingredients entity directly from Meal. However, as illustrated in the controller action method, you can access the association entity (Meals-Ingredients) from the Meal entity. From the association entity, you can access the Ingredients entity to get the list of ingredients. The view would look something like this:

<%@ Page Language="C#" MasterPageFile="~/Views/Shared/Site.Master" Inherits="ViewPage" %>


    
<%= Model.Title %>
    
<%= Model.Description %>
    

    
Ingredients:
    

        <% foreach(Ingredient item in Model.Ingredients) 
           { %>
            
<%= item.Name %>
        <% } %>
    
    

    <%= Html.ActionLink("Update", "Edit", new { id = Model.Meal_ID }) %> |
    <%= Html.ActionLink("Add Ingredient", "IngredientCreate", new{ id = Model.Meal_ID }) %> |
    <%= Html.ActionLink("Delete", "Delete", new { id = Model.Meal_ID }) %> |
    <%= Html.ActionLink("Back to Menu List", "Index") %>

If your database schema is correctly set up with the foreign key relationships you require, this approach should give you the outcome you're looking for.