public class WorkOrder1
    {
        public int Id { get; set; }
        public string Accepter { get; set; }
        public string Foreman { get; set; }
        public string myDate { get; set; }
        public ICollection<GuideWorkTypeStandardHour1> GuideWorkTypeStandardHour1s { get; set; }
        public WorkOrder1()
        {
           GuideWorkTypeStandardHour1s = new List<GuideWorkTypeStandardHour1>();
        }
    }

public class GuideWorkTypeStandardHour1
    {
        public int Id { get; set; }
        public string CodeWork { get; set; }
        public ICollection<WorkOrder1> WorkOrder1s { get; set; }
        public GuideWorkTypeStandardHour1()
        {
            WorkOrder1s = new List<WorkOrder1>();
        }

    }

private void button1_Click_1(object sender, EventArgs e)
        {
            WorkOrder1 wo = new WorkOrder1();
            wo.myDate = maskedTextBoxData.Text;
            wo.Accepter = textBoxAccepter.Text;
            wo.Foreman = textBoxForeman.Text;
            wo.BestPractice = textBox4Recommendation.Text;

            db.WorkOrders.Add(wo);
            db.SaveChanges();

        }

List<GuideWorkTypeStandardHour1> guideWorkTypeStandardHour1;
WorkOrder1 workOrder1 = db.WorkOrders.Find(ListWorkOrders.workorderselectedId);

var works = db.GuideWorkTypeStandardHour1s;

foreach(var w in works)
{
    if(workOrder1.GuideWorkTypeStandardHour1s.Contains(w))
    {
        guideWorkTypeStandardHour1.Add(w);
    }
}

public class WorkOrder1
{
    public int Id { get; set; }
    public string Accepter { get; set; }
    public string Foreman { get; set; }
    public string myDate { get; set; }

    [ForeignKey("Id")]
    public virtual ICollection<GuideWorkTypeStandardHour1> GuideWorkTypeStandardHour1s { get; set; }
    public WorkOrder1()
    {
       GuideWorkTypeStandardHour1s = new List<GuideWorkTypeStandardHour1>();
    }
}

public class GuideWorkTypeStandardHour1
{
    public int Id { get; set; }
    public string CodeWork { get; set; }

    [ForeignKey("Id")]
    public virtual ICollection<WorkOrder1> WorkOrder1s { get; set; }
    public GuideWorkTypeStandardHour1()
    {
        WorkOrder1s = new List<WorkOrder1>();
    }
}

public virtual ICollection<GuideWorkTypeStandardHour1> GuideWorkTypeStandardHour1s { get; set; }

var order =  db.WorkOrder
    .Where(x=>x.Id==512)
    .Include(x=>x.GuideWorkTypeStandardHour1s);

var order =  db.WorkOrder
    .Where(x=>x.Id==512)
    .Include("GuideWorkTypeStandardHour1s");

[ForeignKey("Id")]
public virtual ICollection<GuideWorkTypeStandardHour1> GuideWorkTypeStandardHour1s { get; set; }