Asp.Net Core 3.1 MVC Run the query only once when running the program?

As far as I know, if you want to run dbcontext when the application started, I suggest you could try to asp.net core lifetime method to run codes in the Configure method.

More details, you could refer to below codes:

In the startup.cs Configure method add below codes:

        lifetime.ApplicationStarted.Register(
         () => AddLogs(app));

Addlogs method:

    static void AddLogs(IApplicationBuilder app)
    {

        using (var serviceScope = app.ApplicationServices.CreateScope())
        {
            //Check the table or role is exsited or not to make sure below codes will just start once.
            if (true)
            {

                var context = serviceScope.ServiceProvider.GetService<TestDbcontext>();

                var list = context.Admissions.ToList();
                //dbcontext.Admissions.Add(new Admission() { });
                context.SaveChanges();
            }

        }
    }

Result:

Update:

lifetime is a parameter which we could passed to the startup.cs Configure method:

public void Configure(IApplicationBuilder app, IWebHostEnvironment env, IHostApplicationLifetime lifetime)