How do you construct Entity Framework Core IdentityDbContext<> outside of a service? - entity-framework

Question

I was curious as generally you can do this WITHOUT IdentityDbContext:
public class SomeContext : DbContext
{
protected override void OnConfiguring(DbContextOptionsBuilder optionsBuilder)
{
if (!optionsBuilder.IsConfigured)
{
//I am using Postgres but will also accept answers to SQL Server as I want both ultimately
optionsBuilder.UseNpgsql(#"Host=localhost;Database=someDb;Username=user;Password=yeah");
}
}
}
But when I go to the 'IdentityDbContext<(POCOUser)>' my OnConfiguring method disappears. And it appears this is really not wired up anymore except if I am starting up a service and doing something similar to the Startup of:
services.AddDbContext<SomeContext>(cfg =>
{
cfg.UseSqlServer(_config.GetConnectionString("MyConnectionString"));
});
That's great if I am doing a service and the EF Core is in the same contained project. But what if I am not? Are you not able to specify the connection string on the fly in a constructor or other method on instantiation?

Answer 1

appsettings.json - add connection string:
{
"Logging": {
"LogLevel": {
"Default": "Warning"
}
},
"AllowedHosts": "*",
"ConnectionStrings": {
"SomeDatabase": "Host=localhost;Database=...;Username=...;Password=..."
}
}
Update Startup.cs
public void ConfigureServices(IServiceCollection services)
{
services
.AddMvc()
.SetCompatibilityVersion(CompatibilityVersion.Version_2_2)
.AddJsonOptions(options => options.SerializerSettings.ReferenceLoopHandling = ReferenceLoopHandling.Ignore);
services
.AddEntityFrameworkNpgsql()
.AddDbContext<SomeContext>(options => options.UseNpgsql(Configuration.GetConnectionString("SomeDatabase")))
.BuildServiceProvider();
}
Inject into controller:
private SomeContext _db;
public SomeController(SomeContext someContext)
{
_db = someContext;
}