Web Api, Update DB, connection reset 200ok

Question

I have asp.net web api application. I have the table Companies in the databse which have two fields: id and description. Recently I've updated the database and added a new column called CustomerID. After that when I am trying to call getCompanies

private readonly BackendContext _context;

public CompaniesController(BackendContext context)
{
    _context = context;
}

// GET: api/Companies
[HttpGet]
public IEnumerable<Company> GetCompanies()
{
    return _context.Companies;
}

I get

I think the controller tries to return the old companies model but can't achieve it because it doesnt exist now but I don't know how to fix this though the controller should return the updated model. Maybe I should somehow rebuild the app to make it use the updated version?

Additional code: Context

public class BackendContext : Microsoft.AspNetCore.Identity.EntityFrameworkCore.IdentityDbContext<IdentityUser>//DbContext
    {
        public BackendContext(DbContextOptions<BackendContext> options) : base(options) { }

        public DbSet<Company> Companies { get; set; }
        public DbSet<CompanyToProduct> CompanyToProducts { get; set; }
        public DbSet<Product> Products { get; set; }
        public DbSet<Customer> Customers { get; set; }
        public DbSet<Vendor> Vendors { get; set; }
        public DbSet<VendorToProduct> VendorToProducts { get; set; }
        public DbSet<Invoice> Invoices { get; set; }
        public DbSet<InvoiceItem> InvoiceItems { get; set; }

    }

Model

public class Company
    {
        public int ID { get; set; }
        public string Name { get; set; }
        public string Description { get; set; }

        public int CustomerID { get; set; }
        public virtual Customer Customer { get; set; }

        public virtual ICollection<CompanyToProduct> CompaniesToProducts { get; set; }
        public virtual ICollection<Invoice> Invoices { get; set; }
    }

UPDATE I've added some values to the table and I got the response of the first company:

[{"id":1,"name":"Google","description":"free food","customerID":6,"customer":null,"companiesToProducts":null,"invoices":null}

BUT I also got the fields which is not specified in the table: customer, companiesToProducts,invoices. Invoices and companiesToProducts are tables in my database and I don't know what is customer referred to. I should also mention that these tables are connected by foreign key.

UPDATE
Error:

Answer 1

Based on the comments on the question above, it sounds like the related tables are all trying to serialize and the overall process is failing likely due to circular references in the object graph. This comment above in particular hints at a solution:

I want to return only the data about companies but the controller also returns another fields like customer, companiesToProducts,invoices

While it's convenient to just return directly from the data context, this has the added side-effect of coupling the API with the database (and with the data access framework, which appears to be the issue here). In API design in general it's always a good idea to explicitly define the "shape" of that API. The fields to return, etc.

Project your result into an explicitly defined shape and return only what you want to return:

var result = _context.Companies
                     .Select(c => new 
                     {
                         c.ID,
                         c.Name,
                         c.Description,
                         c.CustomerID
                     })
                     .ToList();

This defines specifically what you want to return, fetches only that information from the backing data, materializes it into an in-memory list, and finally then returns it through the API.

There is a potential downside to this, however. Because now we also need to change the return type of your API method. There are a couple options there, such as returning a generic response object or creating a view model which closely approximates your already existing model and starts to feel like duplication.

As with just about anything, it's a balance. Too far in any one direction and that direction starts to become a problem. Personally I often go the route of defining a view model to return:

public class CompanyViewModel
{
    public int ID { get; set; }
    public string Name { get; set; }
    public string Description { get; set; }
    public int CustomerID { get; set; }
}

and returning that:

return _context.Companies
               .Select(c => new CompanyViewModel
               {
                   ID = c.ID,
                   Name = c.Name,
                   Description = c.Description,
                   CustomID = c.CustomerID
               })
               .ToList();

But the reason I normally do this is because I normally work in an environment where the web application is just one application attached to a common shared business domain, so the view models don't feel like code duplication. They're in a separate project, often take a different shape than the backing data objects, etc. But if your domain models are already in your web project and that's the only project you have, there's a strong desire to want to return those.

Another option when that's the case could be to universally set your JSON serialization to ignore circular references:

services.AddMvc()
          .AddJsonOptions(
                options => options.SerializerSettings.ReferenceLoopHandling
                    = Newtonsoft.Json.ReferenceLoopHandling.Ignore );

But do keep in mind that this still couples your API to your DB models. Maybe that's okay in this project, but if you ever add a column to your DB that you don't want users to see then it becomes an issue. As with anything, you have options.