NullException error in MVC first code entity

Question

I have MVC first code project but I get below error

First code! So there is no default database.

Model class

public class Applicant
{
    public int ApplicantID { get; set; }
    public string UserName { get; set; }
    public string Password { get; set; }
    public int PhoneNumber { get; set; }
}

Context class:

public class Context : DbContext
{
    public List<Applicant> Applicants { get; set; }
    protected override void OnModelCreating(DbModelBuilder modelBuilder)
    {
        modelBuilder.Entity<Applicant>().Property(r => r.ApplicantID)
                     .HasDatabaseGeneratedOption(DatabaseGeneratedOption.Identity);
    }
}

Applicant repasority class:

public  Applicant Create(string username, string password, int phoneNumber, out int existResult)
{
    if (context.Applicants.Where(x => x.UserName == username).ToString() != null)
    {
        applicant = new Applicant()
        {
            UserName = username,
            Password = password,
            PhoneNumber = phoneNumber,
        };
        context.Applicants.Add(applicant);
        existResult = 1;
        return applicant;
    }
    existResult = 0;
    return applicant;   
}

And I added below code to my web.config in my web solution:

  <connectionStrings>
    <add connectionString="Data Source=.;Catalog=Homi;Integrated Security=True" providerName="System.Data.SqlClient" name="Context" />
 </connectionStrings>
</configuration>

Look at this: http://stackoverflow.com/q/4660142/861716. Only *you* can debug your code and check what's null (also applies to `ArgumentNullException`). Side note: `context.Applicants.Where(x => x.UserName == username).ToString()` returns the query string. — Gert Arnold, Jul 03 '16 at 20:47

Muhammad Ehsan Mirzaei · Accepted Answer · 2016-07-08T22:04:40.910

ok I find answer.

first I changed context class to this like below

add this part:

public Context()
    {
        base.Configuration.LazyLoadingEnabled = false;
        base.Configuration.ProxyCreationEnabled = false;
        base.Configuration.ValidateOnSaveEnabled = false;
    }

and changed string to DbSet:

    public DbSet<Applicant> Applicants { get; set; }

second

a cool mistake :D I forgot to do this:

Project –> Manage NuGet Packages…

Note: If you don’t have the Manage NuGet Packages… option you should install the latest version of NuGet

Select the Online tab

Select the EntityFramework package

Click Install

after all for some place of code if above ways doesn't work try{}catch{} was last solution!

and in end when I run my web nothing saved in my db :( it was very important to put "context.SaveChanges();" in applicant repository after "context.Add(applicant);"

that's all tnx

NullException error in MVC first code entity

1 Answers1