nailitdown nailitdown - 2 months ago 32
C# Question

Comparing object properties in c#

This is what I've come up with as a method on a class inherited by many of my other classes. The idea is that it allows the simple comparison between properties of Objects of the same Type.

Now, this does work - but in the interest of improving the quality of my code I thought I'd throw it out for scrutiny. How can it be better/more efficient/etc.?

/// <summary>
/// Compare property values (as strings)
/// </summary>
/// <param name="obj"></param>
/// <returns></returns>
public bool PropertiesEqual(object comparisonObject)
{

Type sourceType = this.GetType();
Type destinationType = comparisonObject.GetType();

if (sourceType == destinationType)
{
PropertyInfo[] sourceProperties = sourceType.GetProperties();
foreach (PropertyInfo pi in sourceProperties)
{
if ((sourceType.GetProperty(pi.Name).GetValue(this, null) == null && destinationType.GetProperty(pi.Name).GetValue(comparisonObject, null) == null))
{
// if both are null, don't try to compare (throws exception)
}
else if (!(sourceType.GetProperty(pi.Name).GetValue(this, null).ToString() == destinationType.GetProperty(pi.Name).GetValue(comparisonObject, null).ToString()))
{
// only need one property to be different to fail Equals.
return false;
}
}
}
else
{
throw new ArgumentException("Comparison object must be of the same type.","comparisonObject");
}

return true;
}

Answer

I was looking for a snippet of code that would do something similar to help with writing unit test. Here is what I ended up using.

public static bool PublicInstancePropertiesEqual<T>(T self, T to, params string[] ignore) where T : class 
  {
     if (self != null && to != null)
     {
        Type type = typeof(T);
        List<string> ignoreList = new List<string>(ignore);
        foreach (System.Reflection.PropertyInfo pi in type.GetProperties(System.Reflection.BindingFlags.Public | System.Reflection.BindingFlags.Instance))
        {
           if (!ignoreList.Contains(pi.Name))
           {
              object selfValue = type.GetProperty(pi.Name).GetValue(self, null);
              object toValue = type.GetProperty(pi.Name).GetValue(to, null);

              if (selfValue != toValue && (selfValue == null || !selfValue.Equals(toValue)))
              {
                 return false;
              }
           }
        }
        return true;
     }
     return self == to;
  }

EDIT:

Same code as above but uses LINQ and Extension methods :

public static bool PublicInstancePropertiesEqual<T>(this T self, T to, params string[] ignore) where T : class
{
    if (self != null && to != null)
    {
        var type = typeof(T);
        var ignoreList = new List<string>(ignore);
        var unequalProperties =
            from pi in type.GetProperties(BindingFlags.Public | BindingFlags.Instance)
            where !ignoreList.Contains(pi.Name)
            let selfValue = type.GetProperty(pi.Name).GetValue(self, null)
            let toValue = type.GetProperty(pi.Name).GetValue(to, null)
            where selfValue != toValue && (selfValue == null || !selfValue.Equals(toValue))
            select selfValue;
        return !unequalProperties.Any();
    }
    return self == to;
}