.Net 5 change DbContext in controller - entity-framework

Question

I have a design where I have one "master" database and multiple "client" databases. When I get a request I lookup in the master database and setup the connection to the right client database.
I'm now trying to design the same in .net 5, where I setup the masterDB in StartUps ConfigureServices():
services.AddDbContext<Models.DataContext.MasterContext>(options =>
options.UseSqlServer("Name=MasterDB"));
I then on the request lookup in the MasterDB as the first thing in every controllers methods and find the connectionString for the clientDB.
But how do I then set it up at that point in time? While also not having to think about disposal of the connection, like when it's passed in using dependency injection, it's handled.
Any advice to do things slightly different are also encouraged.

Answer 1

Inject your MasterContext into a service that provides connection string lookups for your "client" databases (probably with caching). Then use that when resolving and configuring your "client" DbContext.
Something like this:
class ClientDatabaseService
{
MasterDbContext db;
IHttpContextAccessor context;
static Dictionary<string, string> cache = null;
public ClientDatabaseService(MasterDbContext db, IHttpContextAccessor context)
{
this.db = db;
this.context = context;
if (cache == null) RefreshCache();
}
public void RefreshCache()
{
cache = db.Clients.Select(c => new { c.ClientID, c.ConnectionString }).ToDictionary(c => c.ClientID, c => c.ConnectionString);
}
public string GetClientConnectionString()
{
var clientId = context.HttpContext.User.FindFirst("ClientID").Value;
return cache[clientId];
}
}
// This method gets called by the runtime. Use this method to add services to the container.
public void ConfigureServices(IServiceCollection services)
{
services.AddControllers();
services.AddDbContext<MasterDbContext>();
services.AddHttpContextAccessor();
services.AddScoped<ClientDatabaseService>();
services.AddDbContext<ClientDbContext>((services, options) =>
{
var constrService = services.GetRequiredService<ClientDatabaseService>();
var constr = constrService.GetClientConnectionString();
options.UseSqlServer(constr, o => o.UseRelationalNulls());
});
}