CODEWITHSUNDEEP
c#databaseentity-frameworkasp.net-core
42ama
42ama

Reputation: 141

DbSet Find always return null

I'm building url shortener to improve my skills in ASP.NET Core, but came into a problem with using Entity Framework - .Find() method always return null from my database.

First of all, Im created db record class with custom Key field

public class DbField
    {
        [Key]
        public string hash { get; set; }
        public string link { get; set; }
    }

Then applied it in a context

public class UrlShorterContext : DbContext
    {
        public DbSet<DbField> UrlHashes { get; set; }

        public UrlShorterContext(DbContextOptions<UrlShorterContext> options)
            : base(options)
        {
            Database.EnsureCreated();
        }
    }

Add context to services in ConfigureServices with 

string connection = Configuration.GetConnectionString("DefaultConnection");
services.AddDbContext<UrlShorterContext>(options => options.UseSqlServer(connection));

And then applied it in a controller

UrlShorterContext db;

public HomeController(UrlShorterContext context)
{
      db = context;
}


public IActionResult Index(string url,[FromServices] IComputeHash computeService)
        {
            string urlHash = computeService.Compute(url);//generates hash from url
            DbField field = db.UrlHashes.Find(urlHash);
            if (field == null)
            { 
                db.UrlHashes.Add(new DbField { hash = urlHash, link = url });
                return View("View1");
            }
            return View("View2");
...

In first run db is empty, action gets url, hashes it, add's to database and returns "View1". In second run with same url it must be found in .Find() method, field must be assigned to its value and "View2" must be returned. But somehow field get value of null.

Upvotes: 1

Views: 1700

Answers (1)

Stephen Wilson
Stephen Wilson

Reputation: 1514

After adding the hashed url to the UrlHashes DbSet, you need to call .SaveChanges() to make sure the changes are written to the DB.

string urlHash = computeService.Compute(url);//generates hash from url
DbField field = db.UrlHashes.Find(urlHash);

if (field == null)
{ 
    db.UrlHashes.Add(new DbField { hash = urlHash, link = url });
    db.SaveChanges();
    return View("View1");
}

return View("View2");

You should also look into making this action async and calling .SaveChangesAsync()

Upvotes: 3

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