按 null 值过滤的内存数据库不起作用

Question

I've got a working piece of code, that I want to cover with unit tests. However Microsoft's in-memory database returns some unexpected values.

If I query like that

var count = query.Count(c => c.Birthday2000 != null);

the result is 0, although it should be 12.

If I query that way

var count = query.ToList().Count(c => c.Birthday2000 != null);

the result is 12, which was expected.

If I run it with my relational database (mysql) the first line works too.

I've got the following model

public class Customer
{
    public DateTime? BirthDay {get; set; }
    private DateTime? _birthday2000;
    public DateTime? BirthDay2000 
    {
        get
        {
            if (BirthDay == null) _birthday2000 = null;
            else _birthday2000 = new DateTime(2000, BirthDay.Value.Month, BirthDay.Value.Day);
            return _birthday2000;
        }
        set => _birthday2000 = value;
    }
}

What could cause that issue?

My goal is to query the database for the next n birthdays to come. I can't order and filter BirthDay, because the year-portion differs, that's why I introduced a BirthDay2000-property where the year gets set to a fixes year.

I used a custom g/setter to set it automatically when I receive new customers by a webservice.

Answer 1

Not only is your BirthDay2000 invalid as far as mapping EF.Core to a database of any kind (ORMs use data objects, not logic objects), it's fairly invalid as far as properties go in general as well: your getter has side effects.