EF Core strange behaviour

Question

I'm using EF Core 3.0 code first. I have this loop:

foreach (var profileCount in quantity)
{
    //here I get the exception:
    var oldItem = dc.Stock.Items.FirstOrDefault(a => a.Profile.Id == profileCount.Key); 

    if (oldItem == null)
    {
        dc.Stock.Items.Add(new Item
        {
            Price = 0,
            ProfileId = profileCount.Key,
            Quantity = profileCount.Value,
            WasChanged = false
        });
    }
}

Stock.Items is empty(not null). First iteration works fine, on the second one I get

System.NullReferenceException: Object reference not set to an instance of an object.

I guess it's because I add and try to read from the same collection, but I'm not sure why exactly this is happening.

have a looks at `a.Profile.Id` condition. you are setting `profileCount.Key` to `ProfileId ` — Krishna Varma, Feb 19 '20 at 13:00
Does this answer your question? [What is a NullReferenceException, and how do I fix it?](https://stackoverflow.com/questions/4660142/what-is-a-nullreferenceexception-and-how-do-i-fix-it) — Ian Kemp, Feb 19 '20 at 13:11

Johnathan Barclay · Accepted Answer · 2020-02-19T13:07:44.757

1

When you insert your first item (dc.Stock.Items.Add(new Item) you don't add a Profile, so on the next iteration a.Profile.Id will be a NullReferenceException.

Either assign a Profile when you add a new item, or check for null in your FirstOrDefault.

edited Feb 19 '20 at 13:07

answered Feb 19 '20 at 12:59

Johnathan Barclay

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Thanks, it was the case – Jamil Feb 19 '20 at 13:06

EF Core strange behaviour

1 Answers1