Child object not saving into the DB, using Entity Framework Code First

Question

I have a parent object which has the collection of the child objects. I want to save this data into the DB using EF Code First. For some strange reason the parent object gets saved but the child objects not.

Here's my code:

class Person
{
        public Person()
        {
            Operations = new ICollection<Operation> ();
        }

    public int Id { get; set; }

    public virtual ICollection<Operation> Operations { get; set; }
}


public class Operation
{
    public int Id { get; set; }

    public string Data { get; set; }

    public int PersonId { get; set; }

    public virtual Person Person{ get; set; }
}

Here's thee DAL UpdateMethod:

public bool UpdatePerson entity)
{

   //_context.Set<Person>().AddOrUpdate(entity);
   var entityInDb = _context.Persons.Find(entity.Id);

   _context.Entry(entityInDb).CurrentValues.SetValues(entity);
   _context.Entry(entityInDb).State = EntityState.Modified;

   return _context.SaveChanges() > 0;
}

And here's the BLL:

   //Create a new person if it does not exist. If exists, add only the Operations:

       //check if such the person exists in the DB
       var person = Repository.Filter(p=>p.Id == Id)
                    .AsNoTracking().FirstOrDefault();


        //if not, create a new record
        if(person == null)
        {
            personNew = new Person{
                 ...
            };
            bool res = Repository.Insert(personNew );

            if (res)
            {
                //find newly created person
                person = Repository.Filter(p => p.Id == ...)
                      .AsNoTracking().FirstOrDefault();
            }
        }

//Add Operations to the Person entity and Save them:    
        var op = obj.ToOperationModel();
        op.PersonId = person.Id; 
        person.Operations.Add(op);

        var res2 = Repository.Update(person);

There is no error, the parent object (Person) gets created, res2 returns true, but no Operation is added into the DB

Answer 1

Modify the update method like this;

public bool UpdatePerson entity)
{

   //_context.Set<Person>().AddOrUpdate(entity);
   var entityInDb = _context.Persons.Include(x => x.Operations).FirstOrDefault(x => x.Id == entity.Id);//Add Include for navigation property

   _context.Entry(entityInDb).CurrentValues.SetValues(entity);
   _context.Entry(entityInDb).State = EntityState.Modified;
   _context.Entry(entityInDb).Property(x => x.Operations).IsModified = true; // Add this line
   return _context.SaveChanges() > 0;
}

To establish relationship between the entities, you can use DataAnnotations attributes or Fluent Api. To associate relationships by using DataAnnotations , modify the Operation and Person entities like this;

public class Operation
{
    public int Id { get; set; }

    public string Data { get; set; }

    [ForeignKey("Person")] // Add ForeignKey attribute
    public int PersonId { get; set; }

    public virtual Person Person{ get; set; }
}
public class Person
{
    public Person()
    {
        Operations = new ICollection<Operation> ();
    }
    [Key] // Add key attribute
    public int Id { get; set; }

    public virtual ICollection<Operation> Operations { get; set; }
}