Need assistance restructuring an N-Tier MVC/WEB.API app

Question

Currently have the following N-Tiers:

MVC/API UI <-> BLL / DAL / NLL / Model

Would like to accomplish the following:

MVC/API UI <-> BLL <-+-> DAL <-> Model
                     |
                     \-> NLL

I have a class in the DAL to return the context. However when I try and reference this class I get the following error (which is mentioned several times on StackOverflow, however all do not apply to this case):

A field initializer cannot reference the non-static field, method, or property 'Corporate.Web.API.Controllers.SiteAdminAPIController._oDataBaseContext'

The following code is in my DAL for the dbContext:

using System;
using System.Collections.Generic;
using System.Linq;
using System.Data;
using System.Data.Entity;
using System.Data.Entity.Infrastructure;
using System.Text;
using System.Threading.Tasks;
using Corporate.Web.API.Model;

namespace Corporate.Web.API.DAL
{
    public class DataBaseContext
    {
        public DbContext dbContext()
        {
            Corporate_WebEntities _oContext = new Corporate_WebEntities();
            return _oContext;
        }
    }
}

The following code is in my MVC/API controller:

using System;
using System.Collections.Generic;
using System.Data;
using System.Data.Entity;
using System.Data.Entity.Infrastructure;
using System.Linq;
using System.Net;
using System.Net.Http;
using System.Web.Http;
using System.Web.Http.Description;
using System.Threading.Tasks;
using Corporate.Web.API.Model;
using Corporate.Web.API.DAL;
using Corporate.Web.API.BLL;
...
private readonly DataBaseContext _oDataBaseContext = new DataBaseContext();
private readonly DbContext _oDBContext = _oDataBaseContext.dbContext();

1. What do I need to do to get this mess working properly?
2. What am I Missing?

Answer 1

Doing wrong at the following line:

private readonly DbContext _oDBContext = _oDataBaseContext.dbContext();

(1) instead it should be like following:

public class SiteAdminAPIController : Controller
{
    private readonly DataBaseContext _oDataBaseContext = new DataBaseContext();
    private Corporate_WebEntities _oDBContext;

    public SiteAdminAPIController()
    {
         _oDBContext = _oDataBaseContext.dbContext();
    }
}

(2) Or make it property like below:

private DbContext _oDbContextField;
private DbContext _oDbContext
{
    get{
        if(_oDbContextField == null)
        {
            _oDbContext = _oDataBaseContext.dbContext();
        } 
        return _ODbContext;
    }
}

(3) and third and easy option which many people do not recommend is like make _oDataBaseContext.

Replace below line

private readonly DataBaseContext _oDataBaseContext = new DataBaseContext();

with

private static readonly DataBaseContext _oDataBaseContext = new DataBaseContext();

Update You also need to update dbContext() method's return type.

public class DataBaseContext
{
    public Corporate_WebEntities dbContext()
    {
        Corporate_WebEntities _oContext = new Corporate_WebEntities();
        return _oContext;
    }
}