实体框架 - 未在保存父实体上添加到数据库的新子实体（仅在生产环境中）

Question

I am facing a weird issue in an application. I have the following code which updates a parent entity and add new child entities.

    Item item = db.Items.Find(Id);

    if (newSubItems.Count() > 0)
    {
        newSubItems.ForEach(x =>
        {
            var subItem = new SubItem();
            subItem.Name = x.Name;

            item.SubItems.Add(subItem);
        });
    }

    item.ModifiedAt = DateTime.Now;
    item.ModifiedBy = UserId;

    db.Entry(item).State = EntityState.Modified;

    using (var s = db.Database.BeginTransaction(isolationLevel: IsolationLevel.RepeatableRead))
    {
        await db.SaveChangesAsync();
        s.Commit();

        logger.info("Updated successfully.");
    }

This code is working fine in my local environment. If I supply new sub-items, those are added successfully to the respective table.

The models are given below.

    public partial class Item
    {
        public Item()
        {
            this.SubItems = new HashSet<SubItem>();
        }

        public int Id { get; set; }
        public DateTime ModifiedAt { get; set; }
        public int ModifiedBy { get; set; }
        public virtual ICollection<SubItem> SubItems { get; set; }
    }

    public partial class SubItem
    {
        public int Id { get; set; }
        public string Name { get; set; }
        public int ItemId { get; set; }
        public Item Item { get; set; }
    }

However this is not working in my production environment as expected. Parent entity is updated, but new child entities are not added if there are no existing child entities. I checked the logs and I can see that "Updated successfully" is logged. If there is at-least 1 child entity for the parent, then new child entities are added successfully.

So now as a work around in production environment, I am re-adding the sub-items again after the first save operation using the below code.

    int subItemsCount = db.SubItems.Where(a => a.ItemId == item.Id).Count();

    if (subItemsCount == 0 && newSubItems.Count() > 0)
    {
        logger.info(string.Format("Sub-items are not added for Id - {0}. Adding those again.", item.Id));

        newSubItems.ForEach(x =>
        {
            var subItem = new SubItem();
            subItem.Name = x.Name;
            subItem.ItemId = item.Id;

            db.SubItems.Add(subItem);
        });

        await db.SaveChangesAsync();

        logger.info(string.Format("Sub-items re-added successfully for Id - {0}.", item.Id));
    }

Now at looking the logs from production environment, I can see that the message "Sub-items are not added for Id" is logged many times and sub-items are added successfully in the second save operation.

Wondering if any one know the reason for this weird behavior in specific environment alone.

Answer 1

In your first approach you should check if item.SubItems for null before doing item.SubItems.Add() on it.

If it is null then initialize like item.SubItems = new ICollection<SubItem>();

In your second approach,in this code block you are not assigning ItemId

 newSubItems.ForEach(x =>
        {
            var subItem = new SubItem();
            subItem.Name = x.Name;
            subItem.ItemId = item.Id;/* missing line*/
            db.SubItems.Add(subItem);
        });