Compare objects where some props have different formats

Question

What is the best way to compare all properties of two objects where some of them have different formats (e.g. DateTime in one and DateTime.ToString() with custom format in other)?

I was able to do that by using 2 assertions:

o1.ShouldHave().AllPropertiesBut(dto1 => dto1.Date).EqualTo(o2);
o1.Date.Should().Be(DateTime.Parse(o2.Date));

I would think about the following, but that does not compile because EqualTo<T>() is void.

o1.ShouldHave().AllProperties().But(d => d.Date).EqualTo(o2)
.And.Date.Should().Be((DateTime.Parse(o2.Date));

types are:

public class Dto1
{
    public int ID { get { return 1; } }
    public DateTime Date { get { return DateTime.Now.Date; } }
}

public class Dto2
{
    public int ID { get { return 1; } }
    public string Date { get { return DateTime.Now.Date.ToShortDateString(); } }
}

var o1 = new Dto1();
var o2 = new Dto2();

Answer 1

The first example is typically the best way. However, if you would switch o1 and o2, it might work in a single call. Fluent Assertions will try to convert (using Convert.ChangeType) the actual value of a property to the expected value of the property with the same name. In your particular example, it would try to convert the DateTime in Dto1 to a string in Dto2 before comparing the values. But since the string representation of a DateTime is dependent on the culture of the thread, it would not give you predictable results. However, if you would switch o1 and o2, I wouldn't be surprised if Convert.ChangeType would succesfully convert your short datetime back to a DateTIme object.

As a side-note, my DTOs usually just pass the DateTime to the caller without any string conversion. I believe that the actual representation of the DateTime is purely a UI responsibility.

HTH

Dennis