List items not being passed to the view

Question

For my small web app project I've created a model called Company that includes basic company info & also a list of sales reps from different business partners. This is my Contact Model:

 public class Company
    {
        public int ID { get; set; }
        public string Name { get; set; }
        public string Promo { get; set; } // Yes or No field
        public List<Contact> Contacts { get; set; }
        public class Contact
        {
            [Key]
            public int ContactID { get; set; }
            public int CompanyID { get; set; }
            public string ContactName { get; set; }
            public string ContactNumber { get; set; }
        }
    }

This is how I pass the data into my local database:

var companiesData = new Company[]
        {
            new Company
            {
             Name = "Some name", Promo="Y", Contacts = new List<Contact> { new Contact {ContactName="John Doe", ContactNumber="(828)292-2912", CompanyID=1}, 
           }}, // ... some more contacts
        };
        foreach (Company c in companiesData)
        {
            context.Companies.Add(c);
        }
        context.SaveChanges();

How do I load the contact list items onto the razor view? I'm looking at my database and it's showing a blank field for "Contacts". The rest of the data shows up just fine.

Answer 1

see https://dotnetfiddle.net/xb3g68

entities:

public class Company
{
    [Key]
    public int ID { get; set; }
    public string Name { get; set; }
    public string Promo { get; set; } 
    public virtual List<Contact> Contacts { get; set; }       
}

public class Contact
{
    [Key]
    public int ContactID { get; set; }
    [ForeignKey("Company")]
    public int CompanyID { get; set; }
    public virtual Company Company { get; set; }
    public string ContactName { get; set; }
    public string ContactNumber { get; set; }
}

test harness:

public static void Main()
{
    Console.WriteLine("Hello World");
    FakeDbContext context = new FakeDbContext();
    var companiesData = new Company[]
    {
        new Company
        {
            Name = "Some name", Promo="Y", Contacts = new List<Contact> { new Contact {ContactName="John Doe", ContactNumber="(828)292-2912", CompanyID=1}},
        },
        new Company
        {
            Name = "Another name", Promo="N",  Contacts = new List<Contact> { new Contact {ContactName="Jane Doe", ContactNumber="(828)292-2912", CompanyID=2}},
        },
    };
    foreach (Company c in companiesData)
    {
        context.Companies.Add(c);
        foreach (Contact contact in c.Contacts)
        {
            context.Contacts.Add(contact);  
        }
    }
    context.SaveChanges();
    Console.WriteLine("Save done.");
    var companies = context.Companies.ToList();
    Console.WriteLine("companies.Count: " + companies.Count);
    for (int i = 0; i < companies.Count; i++)
    {
        Console.WriteLine(string.Format("company[{0}].Name: {1}", i,     companies[i].Name));
        for (int j = 0; j < companies[i].Contacts.Count; j++)
        {               
Console.WriteLine(string.Format("company[{0}].Contacts[{1}].ContactName: {2}", i, j, companies[i].Contacts[j].ContactName));
        }
    }
    Console.WriteLine("Bye World");
}

output:

Hello World

Save done.

companies.Count: 2

company[0].Name: Some name

company[0].Contacts[0].ContactName: John Doe

company[1].Name: Another name

company[1].Contacts[0].ContactName: Jane Doe

Bye World

Answer 2

Hi on my final project i did the same with viewmodel because is data from two different tables and give more freedom to change thinks in the future.So i create a a view Model

public class ViewModelContactCompany
{
     public String Name { get; set; }
     List<Contact> contacts { get; set; }
    //etc just a sample
}

Controller

public class Controler
{
//param id is a id from company
//to do a relationship
public Action ControlerDetailsContact(int? id)
{
    ViewModelContactCompany x = new ViewModelContactCompany();
    //Do a linq, sqlquery,etc

    x.Name = "sample"; //get name of company by id;

    for (;;)
    {
        //where id = contact.CompanyID
        //add a new object typeof contact to the viewmodel
        //with the data get from the relationship
        x.contacts.Add(new Contact());
    }

    //and in the final return object viewmodel  to the view 
    return View(x);
 }

}

Now the View

@model /patch.ViewModelContactCompany

and here you get the data on the object return on the controler

What is ViewModel in MVC?

Answer 3

So based on your description, it sounds like you are receiving the model - but the Contacts collection is null or empty.

This is because EntityFrameworkCore needs child sets to be included explicitly using Include on your context Db Set. See here for more information

The code below is an example of how to include child collections in your model with eager loading

public class CompanyController : Controller
{
    // This import is needed for using the 'Include' method.
    using Microsoft.EntityFrameworkCore;

    private ApplicationDbContext _context;
    public CompanyController(ApplicationDbContext context)
    {
        _context = context;
    }
    // GET: /<controller>/
    public IActionResult Index()
    {
        List<Company> viewModelData = _context.Companies.Include(p => p.Contacts).ToList();

        return View(viewModelData);
    }
}

public class Company
{
    public int ID { get; set; }
    public string Name { get; set; }
    public string Promo { get; set; } // Yes or No field
    public List<Contact> Contacts { get; set; }
    public class Contact
    {
        [Key]
        public int ContactID { get; set; }
        public int CompanyID { get; set; }
        public string ContactName { get; set; }
        public string ContactNumber { get; set; }
    }
}

And your Database Context

public class ApplicationDbContext : IdentityDbContext<ApplicationUser>
{
    public ApplicationDbContext(DbContextOptions<ApplicationDbContext> options)
        : base(options)
    {
    }

    protected override void OnModelCreating(ModelBuilder builder)
    {
        base.OnModelCreating(builder);
        // Customize the ASP.NET Identity model and override the defaults if needed.
        // For example, you can rename the ASP.NET Identity table names and more.
        // Add your customizations after calling base.OnModelCreating(builder);
    }

    public DbSet<Company> Companies { get; set; }
    public DbSet<Contact> Contacts { get; set; }
}

View file should set the model like so

@model List<Company>

<h3>Do something with 'Model' here</h3>