Entity Framework - How to get relative file path in seed method

问题

Why is filePath null? Any ideas on how to get the relative filePath?

internal sealed class Configuration : DbMigrationsConfiguration<MvcProject.Models.FileDb>
{
    public Configuration()
    {
        // code here is not relevant to question
    }
    protected override void Seed(MvcProject.Models.FileDb context)
    {    
        string filePath = System.Web.HttpContext.Current.Server.MapPath("~/Content/File.txt");

        // read File.txt using filePath and update the database
    }
}

I have the above code in Configuration.cs file in Migrations folder created when entity framework is set up on an ASP .NET MVC project

When I run "Update-Database -Verbose" in Package Manager Console I get an error that filePath is null.

If I manually set filePath with an absolute URL to the file:

string filePath = "C:/Users/User1/My Documents/Visual Studio 2012/Projects/MvcProject/Content/File.txt";

Everything works fine.

Obviously the goal is to have a relative path to enable work with different developers on different setups.

Truth be told all I need is the file - not necessarily the path. Any help will be appreciated.

回答1:

I use this function to map paths inside the Seed method, not very clean but it works:

private string MapPath(string seedFile)
{
    if(HttpContext.Current!=null)
        return HostingEnvironment.MapPath(seedFile);

    var absolutePath = new Uri(Assembly.GetExecutingAssembly().CodeBase).LocalPath; //was AbsolutePath but didn't work with spaces according to comments
    var directoryName = Path.GetDirectoryName(absolutePath);
    var path = Path.Combine(directoryName, ".." + seedFile.TrimStart('~').Replace('/','\\'));

    return path;
}

then just call it using:

   using (var streamReader = new StreamReader(MapPath("~/Data/MyFile.csv")))

回答2:

As I say , I belive that you call it from a page and the System.Web.HttpContext.Current is null, because MapPath function never return null with a not null input - so you get an exception there.

Try that alternative:

string filePath = HttpRuntime.AppDomainAppPath + "/Content/File.txt";

or

string filePath = HostingEnvironment.MapPath("~/Content/File.txt");

Related question: How to access the HttpServerUtility.MapPath method in a Thread or Timer?

来源：https://stackoverflow.com/questions/16260975/entity-framework-how-to-get-relative-file-path-in-seed-method