Saving changes

Saving changes to context

The SaveChanges method

Each context instance has a ChangeTracker that is responsible for keeping track of changes that need to be written to the database.

As you make changes to instances of your entity classes, these changes are recorded in the ChangeTracker and then written to the database when you call SaveChanges.

The database provider is responsible for translating the changes into database-specific operations (for example, INSERT, UPDATE, and DELETE commands for a relational database).

Using SaveChanges method in Edit action

We need to call the save changes method on the context object every time we make a change to the database state without this the objects are changed only in memory and will not be persisted back to the database!

In our application, the edit action method would need to be modified to include the SaveChanges method as shown below:

public async Task<IActionResult> Edit(int id, [Bind("Id,Title,ReleaseDate,Genre,Price")] Movie movie)
{
    if (id != movie.Id)
    {
        return NotFound();
    }

    if (ModelState.IsValid)
    {
        _context.Update(movie);
        await _context.SaveChangesAsync();
        return RedirectToAction(nameof(Index));
    }
    return View(movie);
}

Note that we are using the case synchronous version of the save changes and hence we are using the async-await in combination as discussed earlier

We need to perform exception handling when we are dealing with database calls - it is omitted from the code above just to keep the example simple!

SaveChanges method in other actions

Similarly, we need to incorporate this method in other action methods as discussed next.

The modified controller

The code for the entire controller after modifying it to include SaveChanges() and making some improvements like using better LINQ methods, along with some exception handling is given below:

Modified MovieController.cs

using Microsoft.AspNetCore.Mvc;
using Microsoft.EntityFrameworkCore;
using MvcMovie.Data;
using MvcMovie.Models;

public class MoviesController : Controller
{
   MvcMovieContext _context;

    public MoviesController(MvcMovieContext context)
    {
        _context = context;
    }

    // GET: Movies
    public async Task<IActionResult> Index()
    {
        return _context.Movie != null ?
                    View(await _context.Movie.ToListAsync()) :
                    Problem("Entity set 'MovieContext.Movie'  is null.");
    }

    // GET: Movies/Details/5
    public async Task<IActionResult> Details(int? id)
    {
        if (id == null || _context.Movie == null)
        {
            return NotFound();
        }

        var movie = await _context.Movie
            .FirstOrDefaultAsync(m => m.Id == id);

        if (movie == null)
        {
            return NotFound();
        }

        return View(movie);
    }

    // GET: Movies/Create
    public IActionResult Create()
    {
        return View();
    }

    // POST: Movies/Create
    // To protect from overposting attacks, enable the specific properties you want to bind to.
    // For more details, see http://go.microsoft.com/fwlink/?LinkId=317598.
    [HttpPost]
    [ValidateAntiForgeryToken]
    public async Task<IActionResult> Create([Bind("Id,Title,ReleaseDate,Genre,Price")] Movie movie)
    {
        if (ModelState.IsValid)
        {
            _context.Add(movie);
            await _context.SaveChangesAsync();
            return RedirectToAction(nameof(Index));
        }
        return View(movie);
    }

    // GET: Movies/Edit/5
    public async Task<IActionResult> Edit(int? id)
    {
        if (id == null || _context.Movie == null)
        {
            return NotFound();
        }

        var movie = await _context.Movie.FindAsync(id);
        if (movie == null)
        {
            return NotFound();
        }
        return View(movie);
    }

    // POST: Movies/Edit/5
    // To protect from overposting attacks, enable the specific properties you want to bind to.
    // For more details, see http://go.microsoft.com/fwlink/?LinkId=317598.
    [HttpPost]
    [ValidateAntiForgeryToken]
    public async Task<IActionResult> Edit(int id, [Bind("Id,Title,ReleaseDate,Genre,Price")] Movie movie)
    {
        if (id != movie.Id)
        {
            return NotFound();
        }

        if (ModelState.IsValid)
        {
            try
            {
                _context.Update(movie);
                await _context.SaveChangesAsync();
            }
            catch (DbUpdateConcurrencyException)
            {
                if (!MovieExists(movie.Id))
                {
                    return NotFound();
                }
                else
                {
                    throw;
                }
            }
            return RedirectToAction(nameof(Index));
        }
        return View(movie);
    }

    // GET: Movies/Delete/5
    public async Task<IActionResult> Delete(int? id)
    {
        if (id == null || _context.Movie == null)
        {
            return NotFound();
        }

        var movie = await _context.Movie
            .FirstOrDefaultAsync(m => m.Id == id);
        if (movie == null)
        {
            return NotFound();
        }

        return View(movie);
    }

    // POST: Movies/Delete/5
    [HttpPost, ActionName("Delete")]
    [ValidateAntiForgeryToken]
    public async Task<IActionResult> DeleteConfirmed(int id)
    {
        if (_context.Movie == null)
        {
            return Problem("Entity set 'MovieContext.Movie' is null.");
        }
        var movie = await _context.Movie.FindAsync(id);
        if (movie != null)
        {
            _context.Movie.Remove(movie);
        }

        await _context.SaveChangesAsync();
        return RedirectToAction(nameof(Index));
    }

    private bool MovieExists(int id)
    {
        return (_context.Movie?.Any(e => e.Id == id)).GetValueOrDefault();
    }
}

Run the app

Id column creates issues

The application is now in a state where it can run but if you notice only the edit and delete functionalities work well. The create and edit functionalities will throw exceptions because we are not supposed to modify the ID property of the movie model. This is because of conventions used in entity framework which we will talk about next.