There are two main ways of achieving this. Let's look at an object - Brochure: { ProductId, Year, Month, ProductName}. We want:

• ProductId
• Year
• Month

To make up the primary key.

Method 1 - Data annotations

In your entity class, simply decorate any properties that you want to make up your key with the attribute "Key":

public class Brochure 
{ 
  [Key, Column(Order = 0)] 
  public int ProductId { get; set; }

  [Key, Column(Order = 1)]
  public int Year { get; set; }

  [Key, Column(Order = 3)] 
  public int Month { get; set; }

  [Required] 
  public string ProductName { get; set; } 
}

Method 2 - DbMigration class

NOTE: You shouldn't need to use this method if you are using full entity framework code first. However, some projects only use entity framework to handle migrations - so this might be of use to you:

public partial class BrochureTable : DbMigration 
{ 
  public override void Up() 
  { 
    CreateTable("Brochures", c => new 
      { 
        ProductId = c.Int(nullable: false), 
        Year = c.Int(nullable: false), 
        Month = c.Int(nullable: false), 
        ProductName = c.String(maxLength: 60) 
      }
    ).PrimaryKey(bu => new {bu.ProductId, bu.Year, bu.Month}); 
  } 
}

Enjoy!