Initialize database table from existing .tsv file

Question

I have an ASP.NET MVC 5 project and I want to fill a certain table in the database with information from a .tsv file.

These are what the first 3 lines of the file look like:

CAE_Num CAE_Description
01111   Description 1
01112   Description 2

So I made a model/class that looks like this:

namespace project.Models
{
public class CAE
{
    public int Id { get; set; } // id

    public int CAE_Num { get; set; }
    public string CAE_Description { get; set; }

    public static CAE FromTsv(string tsvLine)
    {
        string[] values = tsvLine.Split('\t');

        CAE cae = new CAE();
        cae.CAE_Num = Convert.ToInt32(values[0]);
        cae.CAE_Description = Convert.ToString(values[1]);

        return cae;
    }
}
}

The model includes a function that splits a string and creates a CAE object based on it.

In order to fill the database before runtime, I decided to use the Seed method in the Configuration class, created when you enable database migrations. I've used this in a different project before, for user roles, so I know this is one of the right places I can achieve what I want. So here's what I did:

namespace project.Migrations
{
using System;
using System.Data.Entity;
using System.Data.Entity.Migrations;
using System.Linq;
using project.Models;
using System.IO;
using System.Collections.Generic;
using System.Web;

internal sealed class Configuration : DbMigrationsConfiguration<ApplicationDbContext>
{
    public Configuration()
    {
        AutomaticMigrationsEnabled = false;
    }

    protected override void Seed(ApplicationDbContext context)
    {
        List<CAE> listCAEs = File.ReadAllLines(HttpContext.Current.Server.MapPath("~/App_Data/CAE.tsv")) // reads all lines into a string array
                .Skip(1) // skip header line
                .Select(f => CAE.FromTsv(f)) // uses Linq to select each line and create a new Cae instance using the FromTsv method.
                .ToList(); // converts to type List

        listCAEs.ForEach(s => context.CAEs.Add(s));
        context.SaveChanges();
    }
}
}

When I run update-database I get the error/warning:

Object reference not set to an instance of an object.

and my model isn't filled at all when I go to localhost:xxxx/CAEs, nor is any information added to the dbo.CAEs [Data] table in the Server Explorer.

I am wondering if my issue is with the path to the .tsv file. I googled and I read that having the file in the App_Data folder saves me the trouble of hardcoding a file path.

Your issue is null HttpContext. http://stackoverflow.com/questions/19323437/how-to-get-file-path-in-entity-framework-seed-method-without-httpcontext-execut/20070329#20070329 — Steve Greene, Jul 04 '16 at 18:58

score 0 · Accepted Answer · edited May 23 '17 at 12:16

For anyone reading this in the future, I placed the function from SteveGreene's link in the Configuration class, above all other methods. In this function I only changed AbsolutePath to LocalPath.

Then on the Seed method I changed the line

List<CAE> listCAEs = File.ReadAllLines(HttpContext.Current.Server.MapPath("~/App_Data/CAE.tsv"))

to

List<CAE> listCAEs = File.ReadAllLines(MapPath("~/App_Data/CAE.tsv"))

Initialize database table from existing .tsv file

1 Answers1