Using Views like tables in Entity Framework Code-first Existing database approach - entity-framework-6

Question

I currently have a working WPF project that is using 2 tables from a sample Northwind database. Using Entity Framework code-first from an existing database these tables are displayed in master-detail format. I would like to use two views instead of the two tables.
I have found several tutorials and have implemented accordingly but for some reason I cannot get the dbcontext to read from the views. I created two views each matching the tables. I modified the class for the view to use [Table("vView")] and assigned a [Key] to create a primary key on the view but still no success. All research shows is to treat the view as if it was a table and all code should be the same. I am using Products and Categories table from Northwind database to test. I created their corresponding views vProducts and vCategories in the Northwind database.
Here is the code that works using the tables Products and Categories generated from the Entity Data Model (code-first):
Category.cs
namespace WPFCodeFirstExisting
{
using System.Collections.Generic;
using System.ComponentModel.DataAnnotations;
using System.ComponentModel.DataAnnotations.Schema;
public class Category
{
[System.Diagnostics.CodeAnalysis.SuppressMessage("Microsoft.Usage", "CA2214:DoNotCallOverridableMethodsInConstructors")]
public Category()
{
Products = new HashSet<Product>();
}
public int CategoryID { get; set; }
[Required]
[StringLength(15)]
public string CategoryName { get; set; }
[Column(TypeName = "ntext")]
public string Description { get; set; }
[Column(TypeName = "image")]
public byte[] Picture { get; set; }
[System.Diagnostics.CodeAnalysis.SuppressMessage("Microsoft.Usage", "CA2227:CollectionPropertiesShouldBeReadOnly")]
public virtual ICollection<Product> Products { get; set; }
}
}
Products.cs
namespace WPFCodeFirstExisting
{
using System.ComponentModel.DataAnnotations;
using System.ComponentModel.DataAnnotations.Schema;
public class Product
{
public int ProductID { get; set; }
[Required]
[StringLength(40)]
public string ProductName { get; set; }
public int? SupplierID { get; set; }
public int? CategoryID { get; set; }
[StringLength(20)]
public string QuantityPerUnit { get; set; }
[Column(TypeName = "money")]
public decimal? UnitPrice { get; set; }
public short? UnitsInStock { get; set; }
public short? UnitsOnOrder { get; set; }
public short? ReorderLevel { get; set; }
public bool Discontinued { get; set; }
public virtual Category Category { get; set; }
}
}
ProductContext.cs
namespace WPFCodeFirstExisting
{
using System.Data.Entity;
public partial class ProductContext : DbContext
{
public ProductContext()
: base("name=ProductContext")
{
Database.SetInitializer<ProductContext>(null);
}
public virtual DbSet<Category> Categories { get; set; }
public virtual DbSet<Product> Products { get; set; }
protected override void OnModelCreating(DbModelBuilder modelBuilder)
{
modelBuilder.Entity<Product>()
.Property(e => e.UnitPrice)
.HasPrecision(19, 4);
}
}
}
MainWindows.xaml.cs
public partial class MainWindow : Window
{
public ProductContext _context = new ProductContext();
public MainWindow()
{
InitializeComponent();
}
private void Window_Loaded(object sender, RoutedEventArgs e)
{
System.Windows.Data.CollectionViewSource categoriesViewSource = ((System.Windows.Data.CollectionViewSource)(this.FindResource("categoriesViewSource")));
_context.Categories.Where(x => x.CategoryName.Contains("P")).Load();
categoriesViewSource.Source = _context.Categories.Local;
}
App.config:
<connectionStrings>
<add name="ProductContext" connectionString="data source=ABC;initial catalog=Northwind;integrated security=True;MultipleActiveResultSets=True;App=EntityFramework" providerName="System.Data.SqlClient" />
<add name="ProductContextView" connectionString="data source=ABC;initial catalog=Northwind;integrated security=True;MultipleActiveResultSets=True;App=EntityFramework" providerName="System.Data.SqlClient" />
</connectionStrings>
Now if I modify the code to use 2 views instead:
SELECT * FROM [dbo].[vProducts]
SELECT * from [dbo].[vCategories]
these views just contain the select statement from their respective tables.
vCategory.cs:
namespace WPFCodeFirstExisting
{
using System.Collections.Generic;
using System.ComponentModel.DataAnnotations;
using System.ComponentModel.DataAnnotations.Schema;
[Table("vCategories")]
public class vCategory
{
[System.Diagnostics.CodeAnalysis.SuppressMessage("Microsoft.Usage", "CA2214:DoNotCallOverridableMethodsInConstructors")]
public vCategory()
{
vProducts = new HashSet<vProduct>();
}
[Key]
public int CategoryID { get; set; }
[StringLength(15)]
public string CategoryName { get; set; }
[Column(TypeName = "ntext")]
public string Description { get; set; }
[Column(TypeName = "image")]
public byte[] Picture { get; set; }
[System.Diagnostics.CodeAnalysis.SuppressMessage("Microsoft.Usage", "CA2227:CollectionPropertiesShouldBeReadOnly")]
public virtual ICollection<vProduct> vProducts { get; set; }
}
}
vProducts.cs:
namespace WPFCodeFirstExisting
{
using System.ComponentModel.DataAnnotations;
using System.ComponentModel.DataAnnotations.Schema;
[Table("vProducts")]
public class vProduct
{
[Key]
public int ProductID { get; set; }
[Required]
[StringLength(40)]
public string ProductName { get; set; }
public int? SupplierID { get; set; }
[ForeignKey("CategoryID")]
public int? CategoryID { get; set; }
[StringLength(20)]
public string QuantityPerUnit { get; set; }
[Column(TypeName = "money")]
public decimal? UnitPrice { get; set; }
public short? UnitsInStock { get; set; }
public short? UnitsOnOrder { get; set; }
public short? ReorderLevel { get; set; }
public bool Discontinued { get; set; }
public virtual vCategory vCategory { get; set; }
}
}
ProductContextView.cs
namespace WPFCodeFirstExisting
{
using System.Data.Entity;
public class ProductContextView : DbContext
{
public ProductContextView()
: base("name=ProductContextView")
{
Database.SetInitializer<ProductContextView>(null);
}
public DbSet<vCategory> vCategories { get; set; }
public DbSet<vProduct> vProducts { get; set; }
protected override void OnModelCreating(DbModelBuilder modelBuilder)
{
modelBuilder.Entity<vProduct>()
.Property(e => e.UnitPrice)
.HasPrecision(19, 4);
}
}
}
MainWindow.xaml.cs
public partial class MainWindow : Window
{
public ProductContextView _context = new ProductContextView();
public MainWindow()
{
InitializeComponent();
}
private void Window_Loaded(object sender, RoutedEventArgs e)
{
System.Windows.Data.CollectionViewSource categoriesViewSource = ((System.Windows.Data.CollectionViewSource)(this.FindResource("categoriesViewSource")));
_context.vCategories.Where(x => x.CategoryName.Contains("P")).Load();
categoriesViewSource.Source = _context.vCategories.Local;
}
When I run using the ProductContextView, These lines do not return any data;
_context.vCategories.Where(x => x.CategoryName.Contains("P")).Load();
categoriesViewSource.Source = _context.vCategories.Local;
I even tried doing something very simple like the following:
var prods = _context.Database.SqlQuery<vCategory>("Select * from dbo.vCategories");
foreach (var p in prods)
{
string test = p.CategoryName.ToString();
}
but prods doesn't return any data either. This test works perfectly fine when using the tables.
I'm hoping to just replace the tables with views using EF. I do not want to use any CRUD operations with the views they are fine being read-only.

Answer 1

What I found is that in code-first if you add a class representing a view as dbSet when the database is seeded it will create what you want to be a view as a table (probably why you are getting no results).
A work around is to create a custom an initializer :
public class CustomDBInitializer : CreateDatabaseIfNotExists<ProductContextView>
{
protected override void Seed(ProductContextView context)
{
base.Seed(context);
}
}
Then after the base seed method use...
context.Database.ExecuteSqlCommand()
...to drop the generated tables and run a SQL script that generates the views to replace them.
You can then use the dbset like a table but it will actually be using the view.
Also not sure why you created to separate contexts.