Variable context in ASP.NET MVC (C#)

Question

In my ASP.NET MVC project (written in C#), I want to use the right DbContext according some value from some condition. That DbContext should be available for all the methods of the controller. To do that, I used the following approach:

First, I built the application with all the contexts I need:

builder.Services.AddDbContext<Context1>(options => options.UseMySql(conection1, ServerVersion.AutoDetect(conection1)));
builder.Services.AddDbContext<Context2>(options => options.UseMySql(conection2, ServerVersion.AutoDetect(conection2)));
builder.Services.AddDbContext<Context3>(options => options.UseMySql(conection3, ServerVersion.AutoDetect(conection3)));
....

Second, for each DbContext added to the builder, I created the respective model class:

namespace Project.Models
{
    public class Context1 : Context0 
    {
        public Context1(DbContextOptions<Context0> options): base(options)
        {
        }

        public DbSet<Table1> Table1 { get; set; }
        public DbSet<Table2> Table2 { get; set; }
        // ....
    }
}

namespace Project.Models
{
    public class Context2 : Context0 
    {
        public Context2(DbContextOptions<Context0> options): base(options)
        {
        }

        public DbSet<Table1> Table1 { get; set; }
        public DbSet<Table2> Table2 { get; set; }
        // ....
    }   
}

Were Context0 has its own model class:

namespace Project.Models
{
    public class Context0 : DbContext 
    {
        public Context0(DbContextOptions options): base(options)
        {
        }

        public DbSet<Table1> Table1 { get; set; }
        public DbSet<Table2> Table2 { get; set; }
        // ....
    }
}

All the models have the same set of DbSets.

Third, my goal is to use the Context0 on my controller after I assign the right injected context:

namespace Project.Controllers
{
    public class HomeController : Controller
    {
        private Context0 MainContext;
        private readonly Context1 InjectedContext1;
        private readonly Context2 InjectedContext2;
        private readonly Context3 InjectedContext3;
        // ....

        public HomeController(Context1 context1,
                              Context2 context2,
                              Context3 context3,
                              ....)
        {
            InjectedContext1 = context1;
            InjectedContext2 = context2;
            InjectedContext3 = context3;
            // ....

            if (some condition)
            {
                MainContext = InjectedContext2; 
            }
        }
    }
}

The problem: when I try to use the MainContext on any method of the controller, I get an error:

System.ArgumentNullException: 'Value cannot be null.'

The error is raised on this line:

Data1 = MainContext.Table1.ToList();

Where MainContext is null.

However (this is important):

• #1: the InjectedContext2 is correctly assigned to MainContext (I can see that at runtime)

• #2: the InjectedContext2 is properly injected to the controller (when I write InjectedContext2.Table1.ToList() instead of MainContext.Table1.ToList(), I got no error and the method works fine)

It looks like the lifecycle of the MainContext doesn't endure through the controller, if you know what I mean. It's assigned, yes, but doesn't have any data "inside" of it.

Does anyone have a solution? Thanks