SqlException: Cannot attach the file as database.

• Open Package Manager Console

• Remove the LocalDB instance if it exists.

  SqlLocalDB i
  SqlLocalDB p "MSSQLLocalDB"
  SqlLocalDB d "MSSQLLocalDB"

• Delete all *.mdf files in the App_Data folder.

• Delete Migration folder if it exists.

• Rebuild project Ctrl + B

• Enable Code-First Migration

  # Enable-Migrations -ContextTypeName <DbContext class FullName>
  # Example:
  Enable-Migrations -ContextTypeName FUStudentMVC.Models.FUDBContext
  # (Optional) Restore `Configuration.cs` content to populate database
  Update-Database

SqlException: Directory lookup for the file ...

• Manually create the App_Data folder.