Navigation property -> Foreign Key

    class Category
    {
        private ICollection<Post> posts;

        public Category()
        {
            this.posts = new HashSet<Post>();
        }

        public int CategoryId { get; set; }

        //virtual -> lazy loading Entity Framework
        public virtual ICollection<Post> Posts
        {
            get { return this.posts; }

            set { this.posts = value; }
        }

    }

    class Post
    {
    //primary key -> automatic set by Entity Framework id or class name + id
        public int PostId { get; set; }

        public string Title { get; set; }

        public string Content { get; set; }

        //foreign key -> automatic set by Entity Framework
        public int CategoryId { get; set; }

        //navigation property
        public virtual Category Category { get; set; }
    }