Change SQL Server Connection String Dynamically inside an ASP.Net Core application - sql-server

Question

I open one database at the start, then need to open another database based on user selecting two values. The database selection has to be at run-time and will change every time.
Have tried to access the Connection String using the Connection String class and have tried other options like Singleton which I do not understand. I am running this on a local Windows 10 system running SQL Server Express. Am coding using Asp.Net Core 2.1
> ASP.Net Core v2.1
Building multi tenant, multi year application
Every client will have one SQL DATABASE per year
I hope to have a table with the following structure
COMPANY_CODE VARCHAR(3),
COMPANY_YEAR INT,
COMPANY_DBNAME VARCHAR(5)
Sample Data
COMPANY_CODE: AAD
COMPANY_YEAR: 19
COMPANY_DB: AAD19
COMPANY_CODE: AAD
COMPANY_YEAR: 18
COMPANY_DB: AAD18
COMPANY_CODE: AAD
COMPANY_YEAR: 17
COMPANY_DB: AAD17
So, every company will multiple rows - one for each financial year.
The COMPANY_DB column will store the DB name to open for that session.
Once the user is authenticated, I want to change the connection string to point to the database in the COMPANY_DB column of the selected row and then let the logged in user perform transactions.
I am unable to figure out how to change the connection string that is embedded in startup.cs.
Any tips on how to achieve this will be most appreciated.

Answer 1

I figured out that you are using one DbContext class for each database. See here for more information: docs.
Remove AddDbContext from Startup, remove OnConfiguring from DbContext and pass options to the constructor.
public class BloggingContext : DbContext
{
public BloggingContext(DbContextOptions<BloggingContext> options)
: base(options)
{ }
public DbSet<Blog> Blogs { get; set; }
}
Then, write service providing DbContext:
public interface IBlogContextProvider
{
BlogContext GetBlogContext(string connectionString);
}
public class BlogContextProvider : IBlogContextProvider
{
BlogContext GetBlogContext(string connectionString)
{
var optionsBuilder = new DbContextOptionsBuilder<BloggingContext>();
optionsBuilder.UseSqlServer(connectionString);
return new BlogContext(optionsBuilder);
}
}
Add service in your Startup.cs:
services.AddScoped<IBlogContextProvider, BlogContextProvider>();
Now you can use DI:
public class HomeController : Controller
{
private IBlogContextProvider _provider;
public HomeController(IBlogContextProvider provider)
{
_provider = provider;
}
public ActionResult Index()
{
using (var context = _provider.GetBlogContext(<your connection string>))
{
//your code here
}
return View();
}
}
EDIT: Of course, you can write ContextProvider as generic.