c# - Entity Framework Core Using multiple DbContexts

Question

I'm having a problem that when I try to access a field in my PartsDbContext I get the following error:

System.Data.SqlClient.SqlException: 'Invalid object name 'fieldName''

It seems that this is because I'm trying to make my PartsDbContext use the same database as my ApplicationDbContext which is used with Identity. I need to know how to setup a 2nd dbcontext to work with EF core that uses/creates a different database.

I've tried creating a 2nd connection string but that gets me this error:

System.Data.SqlClient.SqlException: 'Cannot open database "PartsDb" requested by the login. The login failed. Login failed for user 'DESKTOP-4VPU567higle'.'

Here's my code:

appsettings.json

"ConnectionStrings": {
    "DefaultConnection": "Server=(localdb)\mssqllocaldb;Database=aspnet-PrecisionCustomPC-b14db89e-86ad-4855-a17f-ac64a04339aa;Trusted_Connection=True;MultipleActiveResultSets=true",
    "PartsConnection":  "Server=(localdb)\mssqllocaldb;Database=PartsDb"
},
"Logging": {
    "IncludeScopes": false,
    "LogLevel": {
        "Default": "Warning"
    }
}

PartsDbContext.cs

public class PartsDbContext : DbContext
{
    public DbSet<PartsViewModels.Tower> Towers { get; set; }
    public DbSet<PartsViewModels.Motherboard> Motherboards { get; set; }

    public PartsDbContext(DbContextOptions<PartsDbContext> options)
        : base(options)
    {
    }
}

Startup.cs

public void ConfigureServices(IServiceCollection services)
{
    // Add framework services.
    services.AddDbContext<ApplicationDbContext>(options =>
         options.UseSqlServer(Configuration.GetConnectionString("DefaultConnection")));

    services.AddIdentity<ApplicationUser, IdentityRole>()
        .AddEntityFrameworkStores<ApplicationDbContext>()
        .AddDefaultTokenProviders();

    services.AddEntityFramework()
        .AddDbContext<PartsDbContext>(options =>
          options.UseSqlServer(Configuration.GetConnectionString("PartsConnection")));

    services.AddMvc();

    services.AddAuthorization(options =>
    {
        options.AddPolicy("RequireAdminRole", policy => policy.RequireRole("Admin"));
    });

    // Add application services.
    services.AddTransient<IEmailSender, AuthMessageSender>();
    services.AddTransient<ISmsSender, AuthMessageSender>();
}

AdminController.cs

[Authorize(Policy = "RequireAdminRole")]
public class AdminController : Controller
{
    private readonly PartsDbContext _context;

    public AdminController(PartsDbContext context)
    {
        _context = context;
    }

    public IActionResult Index()
    {
        return View();
    }

    public IActionResult Towers()
    {
        var model = _context.Towers.ToList();
        return View(model);
    }
}

The line var model = _context.Towers.ToList(); is where the error is showing up.

Once again. I want to setup my PartsDbContext to work with Entity Framework Core in a way that EF-Core will automatically create the database.

Answer 1

I figured it out. This mostly came about because I accidentally deleted the database that Identity was using and I needed to figure out how to get it back.

Apparently there's nothing wrong with my connection string the way it is. I just needed to go into the package manager and type these commands in this order:

1. Add-Migration init -Context PartsDbContext
2. Update-Database -Context PartsDbContext

I found this out because that is what I had to do to get my ApplicationDbContext working again and it turns out that this step is done for you when you create a new MVC Core Web Application in Visual Studio using Individual User Authentication.

So basically the steps for adding more DbContexts is to:

1. Create a DbContext Class
2. Create a Connection string for that DbContext in appsettings.json
3. Add the DbContext to your configured services in Startup.cs
4. Setup the DbContext in the controllers that will use it.
5. Open the package manager and run the 2 lines above. (if "-Context" doesn't work try "--context"
6. Run your program and let EntityFrameworkCore take care of the rest.