Can I have one connecting string for multiple Model classes? - asp.net-mvc

Question

As I understand a connection string is attached to one class only. But what if I have many Model classes? Can I use one connection string for multiple classes?
This is a simple version of my UserModel.cs file:
public class UserModel
{
public int Id { get; set; }
public string Email { get; set; }
}
public class UserTable : DbContext
{
public UserModel GetByEmail(string Email)
{
return this.Database.SqlQuery<UserModel>("SELECT * FROM Users WHERE Email=#Email", new SqlParameter("Email", Email)).SingleOrDefault();
}
}
And this is the connection string:
<connectionStrings>
<add name="UserModel"
connectionString="Server=.\SQLEXPRESS;Database=MyDatabase;User Id=MyUser;Password=MyPassword;"
providerName="System.Data.SqlClient" />
</connectionStrings>
Now lets say I want to add a new Model class named DataTable also derived from DbContext as user table is. Do I need a connection string named the same or can I use the already defined one? What is the conventional way of dealing with multiple Model classes and connection strings?

Answer 1

The DbContext class uses the ConnectionString to make the connection to the database.
You normally have multiple model classes exposed by a DbContext.
It is possible to have multiple DbContext objects that use the same connection string value to connect to the database. In this way, you can separate portions of your model into separate contexts if desired (for example, if you are creating separate assemblies that access different tables but provide similar services to the application).
One caveat to note with EF up to at least 5.0, you cannot use the code-first migrations with multiple DbContexts, one will overwrite the other's changes. The solution to this is to create an aggregated DbContext that is only used for the Migrations process.
I've done this in an app that I built. I used the Unity IoC container, and the built a Plugin Interface that allowed me to pass my ConnectionStringName into my separated DbContexts. An example of the plugin in one of the assemblies was:
public class Bootstrapper : IBootstrapper
{
public void Bootstrap(IUnityContainer container, string connectionStringName)
{
container.RegisterType<ISQService, SQService>();
container.RegisterType<ISQEntities, SQEntities>(
new HierarchicalLifetimeManager(), new InjectionConstructor(connectionStringName));
container.RegisterType<IController, SQController>("SQ");
}
}
My global.asax referenced the bootstrapper class below:
protected void Application_Start()
{
AreaRegistration.RegisterAllAreas();
ModelBinders.Binders[typeof(DataTable)] = new DataTableModelBinder();
RegisterGlobalFilters(GlobalFilters.Filters);
RegisterRoutes(RouteTable.Routes);
Bootstrapper.Initialise();
}
protected void Application_End()
{
Bootstrapper.Dispose();
}
Bootstrapper
public static class Bootstrapper
{
private static IUnityContainer container;
public static void Initialise()
{
container = BuildUnityContainer();
DependencyResolver.SetResolver(new UnityDependencyResolver(container));
}
public static void Dispose()
{
container.Dispose();
}
private static void RegisterPlugins(IUnityContainer theContainer, string wildcard, string connectionStringName)
{
var pluginBootStrappers = from Assembly assembly in wildcard.LoadAssemblies()
from type in assembly.GetExportedTypes()
where typeof(IBootstrapper).IsAssignableFrom(type)
select (IBootstrapper)Activator.CreateInstance(type);
pluginBootStrappers.ToList().ForEach(b => b.Bootstrap(theContainer, connectionStringName));
}
private static IUnityContainer BuildUnityContainer()
{
var theContainer = new UnityContainer();
const string ConnectionStringName = "MyDb";
RegisterPlugins(theContainer, "MyApp.Systems.*.dll", ConnectionStringName);
// Register Application Specific objects
theContainer.RegisterType<IMyEntities, MyEntities>(
new HierarchicalLifetimeManager(),
new InjectionConstructor(ConnectionStringName));
theContainer.RegisterType<IAimaService, AimaService>();
var factory = new UnityControllerFactory(theContainer);
ControllerBuilder.Current.SetControllerFactory(factory);
return theContainer;
}
}

Answer 2

The connection string defines the parameters needed to connect to the DB.
Maybe I think you are talking about or confusing the SQL Query with the connectionstring.
Yes one SQL Query can QUERY more than one table at any given time.
Maybe you could look into the "SQL Query Statement" on google for in depth information.