Mysql with . Net 4.6.2 - Error "Object reference not set for an instance of an object." dbContext class

Question

Dear friends! I have a problem trying to access dbContext with Mysql, for example accessing Context.set(). Add(obj), I get the error message "Object reference not set for an object instance." the project is a simple web api, where the controller accesses the database through a service class that inherits from an abstract class methods for data management (repository class) in the database, inferfaces with standard actions (crud). but still get error.

public class HomeController : Controller
{
    private ContatoService _ContatoService;

    public ActionResult Index()
    {
        return View();
    }

    [HttpPost]
    public void Post(Contato obj)
    {
        _ContatoService = new ContatoService();
        _ContatoService.Post(obj);

    }
}

public class ContatoService : ContatoRepository, IBaseService<Contato>
{
    public void Delete(int id)
    {
        if (id == 0) throw new ArgumentException("Para realizar a exclusão é necessário identificar o registro.");
        Remove(id);
    }

    public Contato Get(int id)
    {
        if (id == 0) throw new ArgumentException("Para realizar a seleção da informação é necessário identificar o registro.");
        return Select(id);
    }

    public List<Contato> Get()
    {
        return SelectAll();
    }

    public Contato Post(Contato obj)
    {
        return Insert(obj);
    }

    public Contato Put(Contato obj)
    {
        return Update(obj);

    }
}

public interface IBaseService<T>
{
    T Post(T obj);
    T Put(T obj);
    void Delete(int id);
    T Get(int id);
    List<T> Get();
}

public class ContatoRepository: BaseRepository<Contato>
{
}

public abstract class BaseRepository<T> : IDisposable, IRepository<T> where T : class
{
    MySQLContext _Context = new MySQLContext();

    public void Dispose()
    {
        _Context.Dispose();
    }

    public T Insert(T obj)
    {
        //-- O erro acontece ao acessar _Context...
        _Context.Set<T>().Add(obj);
        return obj;
    }

    public void Remove(int id)
    {
        if (id == 0) throw new ArgumentException("Para realizar essa ação, é necessário informar um identificador.");
        _Context.Set<T>().Remove(Select(id));
    }

    public T Select(int id)
    {
        if (id == 0) throw new ArgumentException("Para realizar essa ação, é necessário informar um identificador.");
        return _Context.Set<T>().Find(id);
    }

    public List<T> SelectAll()
    {
        return _Context.Set<T>().ToList();
    }

    public T Update(T obj)
    {
        _Context.Entry(obj).State = EntityState.Modified;
        return obj;
    }
}

public interface IRepository<T> where T : class
{
    T Insert(T obj);
    T Update(T obj);
    void Remove(int id);
    T Select(int id);
    List<T> SelectAll();

}

    public class MySQLContext: DbContext
{
    public MySQLContext(): base("MySQLConString") {}

    protected override void OnModelCreating(DbModelBuilder modelbuilder)
    {
        modelbuilder.Conventions.Remove<PluralizingTableNameConvention>();
        modelbuilder.Entity<Contato>().ToTable("site_contato");
    }

    public DbSet<Contato> Contato { get; set; }

}

Answer 1

Luciano, I don’t know if this is your case but it was mine, in this case I received this same message when I needed to insert an object composed of other objects. In my case the properties of the main object were ok, however a given of one of the objects that made up the main object had one of the invalid properties.

If possible put your Contact class. And if it has an object as a property, add it in its context class.

I hope I’ve helped.