Why is the application not using my connection string?

Question

Question.
Why is the application not using my connection string?  

Used by:

• Server - (LocalDB) \ MSSQLLocalDB;
• Entity Framework (EF);

• WPF Framework.

    Goal.
  Make the application work with the database NORTHWINDC.MDF.  

Description.
 I am passing a connection string
сonnectionStringStart = @" Data Source = (localdb)\mssqllocaldb; Initial Catalog = NORTHWINDC.MDF; Integrated Security = True; MultipleActiveResultSets = True ";
into the constructor of the class
class ProductContext: DbContext.

 I am running the application.
 I get a connection string: Data Source=(localdb)\mssqllocaldb;Initial Catalog=WpfAppFrm.ProductContext;Integrated Security=True;MultipleActiveResultSets=True

  Result.
The application creates the database WpfAppFrm.ProductContext and each time it runs it works with the databaseWpfAppFrm.ProductContext.
 
Category.cs

// 
using System.Collections.ObjectModel;
using System.ComponentModel.DataAnnotations;
using System.ComponentModel.DataAnnotations.Schema;

namespace WpfAppFrm
{
    [Table("Categories")]
    public class Category
    {        
        public Category()
        {
            // this.Products = new ObservableCollection<Product>();
        }

        public int CategoryId { get; set; }
        public string Name { get; set; }

        // public virtual ObservableCollection<Product> Products { get; private set; }

    }
}

ProductContext.cs

using System.Data.Entity;

namespace WpfAppFrm
{
    public class ProductContext : DbContext
    {
        // public ProductContext() : base("DefaultConnection")
        public string ConnectionString_test { get; set; }
        public ProductContext(string сonnectionString)
        {
            this.ConnectionString_test = сonnectionString;
        }

        public DbSet<Category> Categories { get; set; }
        // public DbSet<Product> Products { get; set; }
    }
}

MainWindow.xaml.cs

//
using System.ComponentModel;
using System.Data.Entity;

namespace WpfAppFrm
{
    /// <summary>
    /// Логика взаимодействия для MainWindow.xaml
    /// </summary>
    public partial class MainWindow : Window
    {
        public static string сonnectionStringStart;
        private ProductContext _context;

        public MainWindow()
        {
            InitializeComponent();

            сonnectionStringStart = @"Data Source=(localdb)\mssqllocaldb;Initial Catalog=NORTHWINDC.MDF;Integrated Security=True;MultipleActiveResultSets=True";
            _context = new ProductContext(сonnectionStringStart);
        }

        private void Window_Loaded(object sender, RoutedEventArgs e)
        {
            try
            {
                System.Windows.Data.CollectionViewSource categoryViewSource =
                ((System.Windows.Data.CollectionViewSource)(this.FindResource("categoryViewSource")));

                _context.Categories.Load();

                BindingList<Category> _studBindList = _context.Categories.Local.ToBindingList();

                categoryViewSource.Source = _context.Categories.Local;

                AddEntity();
                // GetAll();
                string сonnectionStringStartDuplicate = сonnectionStringStart;
                string connectionStringResult1 = _context.Database.Connection.ConnectionString;
                string connectionStringResult2 = _context.ConnectionString_test;
            }
            catch (Exception ex)
            {
                throw;
            }
        }

        public void AddEntity()
        {
            Category category = new Category
            {
                Name = "Name_Category_4"
            };

            _context.Categories.Add(category);
            string connectionString_str = _context.Database.Connection.ConnectionString;
            _context.SaveChanges();
        }

        public void GetAll()
        {
            _context.Categories.Load();

            BindingList<Category> _studBindList = _context.Categories.Local.ToBindingList();
        }
    }
}

  Installing the Entity Framework

Database NORTHWINDC.MDF

Database WpfAppFrm.ProductContext

The result of debugging the application.

The result of the application.

Application tree.

Answer 1

Instead of having property to store connection string like here

public string ConnectionString_test { get; set; }
public ProductContext(string сonnectionString)
{
    this.ConnectionString_test = сonnectionString;
}

you need to pass connection string to the base constructor of DbContext, which actually uses it

public ProductContext(string сonnectionString) : base(connectionString)
{
}