Cannot attach mdf file as database

Question

I am using VS 2015 to create an ASP.NET MVC project and found the following error:

Cannot attach the file 'F:\MINH\Documents\Visual Studio 2015\Projects\NailShop\NailShop\App_Data\NailShop.Models.TechnicianContext.mdf' as database 'NailShop.Models.TechnicianContext'.

The error is found in the line:

technicianDetails = technicianContext.Technician.Single(x => x.TechnicianID == id);

I see that in Project Explorer/App_Data folder is empty. I didn't delete and thing. This is a fresh project.

My model:

namespace NailShop.Models
{
    [Table("TechnicianDetails")]
    public class TechnicianDetails
    {
        // model fields: 
        [Key]
        public int TechnicianID { get; set; }    // no semicolon
        public int commentID { get; set; }
        public int serviceID { get; set; }
        public string firstName { get; set; }
        public string lastName { get; set; }
        public string introduction { get; set; }
        public int rating { get; set; }
    }
}

My controller:

public class TechnicianDetailsController : Controller
{
    // GET: TechnicianDetails
    public ActionResult TechnicianDetails(int id)
    {
        // Model class:
        TechnicianDetails technicianDetails = new Models.TechnicianDetails();
        // DBContext class:
        TechnicianContext technicianContext = new TechnicianContext();

        // map the row in database table to model : assign the TechnicianID in the db to the parameter technicianID of the action method
        technicianDetails = technicianContext.Technician.Single(x => x.TechnicianID == id);


        return View("~/Views/Technician/TechnicianDetails.cshtml", technicianDetails);
    }
}

My connection string: I assign the connection string by Server Explorer -> Add Connection --> select the server and database --> Advanced --> copy and paste the Data Source. The database is also connectable via Visual Studio Server Explorer

enter image description here

Package manager console:

I followed the steps from Cannot attach the file *.mdf as database and choose the guide "to fix it with SQL Server Management Studio".

I also followed the steps from: Cannot attach the file .mdf as database

I run

SQLLocalDB info

and found 2 instances:

MSSQLLocalDB
ProjectsV12

I then followed to stop, delete, start each instance.

I also ran update-database and get the following error:

enter image description here

Answer 1

I found out the name of the connection string (TechnicianDetailContext) doesn't match with the class inheritting DBContext class that I created (TechnicianContext).

Therefore, Visual Studio will run the TechnicianContext with defaul connection, that points to a different local server as show in attach image:

enter image description here