PropertyInfo.GetValue unable to compare datetimes?

Question

I am looping through two objects to see if all items within the two objects are the same. After adding a watch at the point where it is return false, I see the same values. The two items being compared are both datetime. They have the exact same value, but are returning false. My question is Considering these two items are both datetime, are they causing the issue? If not, is there a better way to compare my two objects?

private bool CompareObj(Visit object1, Visit object2)
{
    foreach (var obj1PropertyInfo in object1.GetType().GetProperties())
    {
        foreach (var obj2PropertyInfo in object2.GetType().GetProperties())
        {
            if (obj1PropertyInfo.Name == obj2PropertyInfo.Name && obj1PropertyInfo.GetValue(object1, null) != obj2PropertyInfo.GetValue(object2, null))
            {
                return false;
            }
        }
    }
    return true;
}

Do they actually have the same value, including ticks/milliseconds? — Douglas Barbin, Aug 05 '14 at 19:36
Use `.Equals`, not `==`. Otherwise you are comparing references of boxed DateTime values instead of the values themselves. — Michael Liu, Aug 05 '14 at 19:36
What was the purpose of this? Would object.Equals(object1, object2) fit? Why not? Can they have different type? What if one have property that the other does not have? — firda, Aug 05 '14 at 19:51
There may be simmilar question: http://stackoverflow.com/questions/506096/comparing-object-properties-in-c-sharp — firda, Aug 05 '14 at 20:00

score 2 · Answer 1 · answered Aug 05 '14 at 19:45

2

Here is a linq way:

return object1
      .GetType()
      .GetProperties()
      .All(x => object.Equals(x.GetValue(object1), x.GetValue(object2));

answered Aug 05 '14 at 19:45

Selman Genç

100,147
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What if I pass in some object with a property with value null? – firda Aug 05 '14 at 19:46
Then you get a `NullReferenceException`, obviously, as this was originally written. `object.Equals` fixes that. – Douglas Barbin Aug 05 '14 at 19:47

score 1 · Accepted Answer · answered Aug 05 '14 at 19:41

1

Use Equals (works for nulls as well)

private bool CompareObj(Visit object1, Visit object2)
{
    foreach (var obj1PropertyInfo in object1.GetType().GetProperties())
    {
        foreach (var obj2PropertyInfo in object2.GetType().GetProperties())
        {
            if (obj1PropertyInfo.Name == obj2PropertyInfo.Name
            && !Equals(obj1PropertyInfo.GetValue(object1, null),
            obj2PropertyInfo.GetValue(object2, null)))
            {
                return false;
            }
        }
    }
    return true;
}

answered Aug 05 '14 at 19:41

firda

3,268
17
30

1

Also you can eliminate nested loop. It is redundant – Sriram Sakthivel Aug 05 '14 at 19:42
Can be reduced if object1.GetType() == object2.GetType() ...but can we assume that? Or can we return false if the type is different? – firda Aug 05 '14 at 19:45
Can be reduced to `return object.Equals(object1, object2);`. If the types aren't the same, then the objects won't be either. – Douglas Barbin Aug 05 '14 at 19:46
Object can be equal even if not of the same type. We need to know what was the purpose first. – firda Aug 05 '14 at 19:52

Douglas Barbin · Answer 3 · 2014-08-05T19:46:11.090

Credit to Michael Lieu for suggesting this first, but I will put it in answer form since he did not.

If you are only interested in object equality (and not whether or not the objects share the same reference), use the .Equals method. By default (i.e., assuming that it is not overloaded), == compares references, which (presumably) are the same in your case because these are 2 different instances of DateTime.

This is all under the assumption that you are comparing 2 DateTime instances, of course: private bool CompareObj(Visit object1, Visit object2) { return object.Equals(object1, object2); }

If you are comparing more complex objects, you may need the loop with reflection to iterate through the properties.

Summary: If you are only interested in equality, but you don't care whether or not the references are identical, use Equals instead of ==.

PropertyInfo.GetValue unable to compare datetimes?

3 Answers3