ASP.NET EF with class library - entity-framework

Question

I created a class library which is going to have my database model with DB first approach. I am using the Northwind database.
public void ConfigureServices(IServiceCollection services)
{
services.AddDbContext<NorthwindContext>(options =>
{
options.UseSqlServer(Configuration.GetConnectionString("NorthwindContext"));
});
}
In this method in asp.net project it tells me that the NorthwindContext is not convertible to DBcontext but the class inherits from it:
Error CS0311
The type 'NorthwindDal.NorthwindContext' cannot be used as type parameter 'TContext' in the generic type or method 'EntityFrameworkServiceCollectionExtensions.AddDbContext(IServiceCollection, Action?, ServiceLifetime, ServiceLifetime)'.
There is no implicit reference conversion from 'NorthwindDal.NorthwindContext' to 'Microsoft.EntityFrameworkCore.DbContext'.
If I don't use the AddDbcontext and try to run the project, it just tells me that it cannot find the connection string for the database.
The context is auto created and it inherits from the DBcontext as well.
I think its probably because I try to use the class library to do this but is there a way to use class library with ASP.NET?
Northwind Context
public partial class NorthwindContext : DbContext
{
public NorthwindContext()
: base("name=NorthwindContext")
{
}
protected override void OnModelCreating(DbModelBuilder modelBuilder)
{
throw new UnintentionalCodeFirstException();
}
public virtual DbSet<Category> Categories { get; set; }
public virtual DbSet<CustomerDemographic> CustomerDemographics { get; set; }
public virtual DbSet<Customer> Customers { get; set; }
public virtual DbSet<Employee> Employees { get; set; }
public virtual DbSet<Order_Detail> Order_Details { get; set; }
public virtual DbSet<Order> Orders { get; set; }
public virtual DbSet<Product> Products { get; set; }
public virtual DbSet<Region> Regions { get; set; }
public virtual DbSet<Shipper> Shippers { get; set; }
public virtual DbSet<Supplier> Suppliers { get; set; }
public virtual DbSet<Territory> Territories { get; set; }
}

Answer 1

Based on your scenario if you would like to implement "database first approach" you could follow the below steps.
Database Schema:
You can download Northwind database schema from our official site as well. Just for reference.
Startup.cs:
public void ConfigureServices(IServiceCollection services)
{
services.AddDbContext<ApplicationDbContext>(options =>
options.UseSqlServer(Configuration.GetConnectionString("DefaultConnection")));
}
Note: You can set any meaningful connection string name here in DefaultConnection as I have set this.
DbContext class:
public class ApplicationDbContext : DbContext
{
public ApplicationDbContext(DbContextOptions<ApplicationDbContext> options) : base(options)
{
}
public DbSet<Categories> Categories { get; set; }
protected override void OnModelCreating(ModelBuilder modelBuilder)
{
modelBuilder.Entity<Categories>().ToTable("Categories");
}
}
appsettings.json:
"ConnectionStrings": {
"DefaultConnection": "Server=YourServerName;Database=Northwind;Trusted_Connection=True;MultipleActiveResultSets=true"
}
Controller:
public class NorthwindController : Controller
{
private readonly MvcAttendanceDbContext _context;
private IHostingEnvironment _hostEnvironment;
public NorthwindController(IHostingEnvironment _environment, MvcAttendanceDbContext context)
{
_hostEnvironment = _environment;
_context = context;
}
public IActionResult Index()
{
var categories = _context.Categories.ToList();
return View(categories);
}
}
View:
#model IEnumerable<MVCApps.Models.Categories>
<h3 class="card-title"><strong>Northwind Category</strong> </h3>
<div class="row">
#foreach (var item in Model)
{
<div class="col-sm-4">
<div class="card" style="width: 18rem;border:1px;padding: 2px 2px 2px 2px; margin-bottom:20px;box-shadow: rgba(0, 0, 0, 0.35) 0px 5px 15px;">
<div class="card-body">
<h5 class="card-title"><strong>#Html.DisplayFor(modelItem => item.CategoryName)</strong> </h5>
<p class="card-text">#Html.DisplayFor(modelItem => item.Description)</p>
<a asp-action="Details" class="btn btn-primary" asp-route-memberId="#item.Description">Details</a> | <a asp-action="EditMember" class="btn btn-warning" asp-route-memberId="#item.CategoryID">Edit</a>
</div>
</div>
</div>
}
</div>
Output:

Answer 2

To generate model classes and database context from an existing database you need to use ef tool scaffolding. You can do it using the command
dotnet ef dbcontext scaffold "Your connection string" Microsoft.EntityFrameworkCore.SqlServer
You need the add reference following NuGet packages if you need to run the command.
dotnet add package Microsoft.EntityFrameworkCore.Design
dotnet add package Microsoft.EntityFrameworkCore.SqlServer