If your table look like:
CREATE TABLE [dbo].[_Partner](
	[Sifra] [int] NOT NULL,
	[Naziv] [nvarchar](70) NULL,
	[Mesto] [nvarchar](50) NULL,
	[Pib] [nvarchar](20) NULL,
	[Adresa] [nvarchar](50) NULL,
	[Region1] [int] NULL,
	[Region2] [int] NULL,
	[Region3] [int] NULL,
	[HRabat] [decimal](18, 2) NULL,
 CONSTRAINT [PK__Partner] PRIMARY KEY CLUSTERED 
(
	[Sifra] ASC
)WITH (PAD_INDEX  = OFF, STATISTICS_NORECOMPUTE  = OFF, IGNORE_DUP_KEY = OFF, ALLOW_ROW_LOCKS  = ON, ALLOW_PAGE_LOCKS  = ON) ON [PRIMARY]
) ON [PRIMARY]
Then your model should look like:
using System;
using System.Data.Entity;
using System.ComponentModel.DataAnnotations;

namespace MvcMovie.Models
{
    [Table("_Partner")]
    public class Partner
    {
      [Key]
      public int Sifra { get; set; }
      public string Naziv { get; set; }
      public string Mesto { get; set; }
      public string Pib { get; set; }
      public string Adresa { get; set; }
      public int? Region1 { get; set; }
      public int? Region2 { get; set; }
      public int? Region3 { get; set; }
      public decimal? HRabat { get; set; }
    }

    public class PartnerDBContext : DbContext
    {
        public DbSet Partners { get; set; }
    }
}

Where int? and decimal? are fields with NULL values.

One example of connection string in web.config is like: