实体框架：将子记录添加到现有父记录中

Question

I need to add a child record to and existing parent.

I call the following methods

_handler.Update(custOrder);
_handler.Save();


public TEntity Update(TEntity entity)
        {
            Entities.Attach(entity);
            DataContext.Entry(entity).State = EntityState.Modified;
            return entity;
        }

and

  public void Save() {
            try
            {
                base.SaveChanges();
            }
            catch (Exception e) { }
        }

The custOrder contains the parent (which already exists) and a new child record that needs to be added. Eg Adding an order item for an existing order.

However when I execute this the child does not get added.

I am not sure how specify that the parent has not changed but a child was added

Please advice.

Answer 1

I finally got the answer it was a bit subtle have to admit, The parent entity needed to be added instead of attached and the state set to modified afterwards.

 public TEntity Update(TEntity entity)
        {
            Entities.Add(entity);
            DataContext.Entry(entity).State = EntityState.Modified;
            return entity;
        }

Answer 2

You need to tell EF that the child itself was actually added. It won't assume from the parent that something needs to be added when the EntityState is set to Modified. You need to Add that new child record to the context, and then run the save.

Assuming OrderItem class as your child:

dbContext.OrderItems.Add(myNewOrderItem);
dbContext.SaveChanges();