What exactly should a model contain in MVC?

Question

I've recently been reading Microsoft's tutorial on ASP.NET Core and seen that the controller classes of that tutorial include LINQ queries to fetch data from a database. A code snippet of that tutrorial for example looks like this:


// GET: Movies
public async Task<IActionResult> Index(string movieGenre, string searchString)
{
    // Use LINQ to get list of genres.
    IQueryable<string> genreQuery = from m in _context.Movie
                                    orderby m.Genre
                                    select m.Genre;

    var movies = from m in _context.Movie
                 select m;

    if (!string.IsNullOrEmpty(searchString))
    {
        movies = movies.Where(s => s.Title.Contains(searchString));
    }

    if (!string.IsNullOrEmpty(movieGenre))
    {
        movies = movies.Where(x => x.Genre == movieGenre);
    }

    var movieGenreVM = new MovieGenreViewModel
    {
        Genres = new SelectList(await genreQuery.Distinct().ToListAsync()),
        Movies = await movies.ToListAsync()
    };

    return View(movieGenreVM);
}

My question is the following: What exactly does a model class contain? In all the articles I read about MVC pattern I am advised to put the functions where I fetch data from a database into a model class. So are they doing a mistake in this tutorial?

Your model should be your entties. In your example the model is the `Movie` entity in which you query the database. This should exist inside the Models folder. Not the db query. Just the Movie class with all its properties. — panoskarajohn, Dec 22 '19 at 19:47
I think the "MVC" framework hides this a bit, but the fetching/updating usually happens much later and sort of behind the scenes... (not when you execute the LINQ query... the lambda hides a lot there... the fetch is probably done when .ToList is called? So there is a super model in the framework handling all those database calls) The "movieGenreVM" model is a "View Model" and is just data to be used in the view. — pcalkins, Dec 23 '19 at 22:12
Also see this post from someone who has a deeper understanding of what MVC means in a web context: https://stackoverflow.com/questions/5863870/how-should-a-model-be-structured-in-mvc/5864000#5864000 — pcalkins, Dec 23 '19 at 22:15

Bianca Grecea · Answer 1 · 2019-12-23T13:48:14.393

A model class is a DTO and you can read more about them here: https://learn.microsoft.com/en-us/aspnet/web-api/overview/data/using-web-api-with-entity-framework/part-5

There is not an error in the code that you have, it is only a bad practice. The main difference between an entity and a DTO is that you do not mention the relation to another DTO. For example, when we talk about Entities we have

public class Author{
public string name{get; set;}
public List<Book> Books {get; set;}
}

But when we talk about DTO we will have only

public class Author{
    public string name{get; set;}
    }

The code will run but you do not want to get the whole properties of the entity, only a few and clearly not the entities related to it. If you do the version they presented, the code will take more to compile and will be prone to error.

What exactly should a model contain in MVC?

1 Answers1