/// <summary>Given an istance of an object T, create a hash for field values we want to track a change in</summary>
/// <typeparam name="T">Object type</typeparam>
/// <param name="obj">object instance</param>
/// <returns></returns>
/// <remarks>
/// https://developer.apple.com/library/content/documentation/Swift/Conceptual/Swift_Programming_Language/AdvancedOperators.html
/// https://msdn.microsoft.com/en-us/library/system.object.gethashcode(v=vs.110).aspx
/// </remarks>
public static int HashByValue <T>(T obj)
{
// get only public instance properties
PropertyInfo[] props = typeof(T).GetProperties(BindingFlags.Public | BindingFlags.Instance);
// track a running hash value
int hash = 0;
foreach (PropertyInfo prop in props)
{
// ignore if not a public read property
if (!prop.CanRead)
{
continue;
}
// get the properties TrackChange attribute
TrackAttribute map = prop.GetCustomAttribute <TrackAttribute>(false);
// has a Track attribute set to true
if (map != null && map.TrackChange)
{
object value = prop.GetValue(obj, null);
if (value == null)
{
hash = hash ^ 0;
}
// make null strings and empty strings cause the same value since they might be read from different sources
else if (prop.PropertyType == typeof(string) && String.IsNullOrWhiteSpace(value.ToString()))
{
hash = hash ^ 0;
}
else
{
hash = hash ^ value.GetHashCode();
}
}
}
return(hash);
}
/// <summary>Forms a string to determine if the object is the same</summary>
/// <remarks>strings are NOT case sensitive</remarks>
public static string HashByString <T>(T obj)
{
// get all the properties in the class
PropertyInfo[] props = typeof(T).GetProperties(BindingFlags.Public | BindingFlags.Instance);
// concatenate every field we care about
StringBuilder sb = new StringBuilder();
foreach (PropertyInfo prop in props)
{
// is this a public read property
if (!prop.CanRead)
{
continue;
}
// get the properties FieldMap attribute
TrackAttribute map = prop.GetCustomAttribute <TrackAttribute>(false);
if (map != null && map.TrackChange)
{
// null values add nothing to the hash
object value = prop.GetValue(obj, null);
if (value == null)
{
continue;
}
// change to switch
if (prop.PropertyType == typeof(string))
{
sb.Append(value.ToString().Trim().ToLower());
}
else if (prop.PropertyType == typeof(bool) || prop.PropertyType == typeof(Nullable <bool>))
{
sb.Append(value.ToString().ToLower()[0]);
}
else if (prop.PropertyType == typeof(DateTime) || prop.PropertyType == typeof(Nullable <DateTime>))
{
sb.Append(value.ToString().ToLower());
}
else if (prop.PropertyType == typeof(int) || prop.PropertyType == typeof(Nullable <int>))
{
sb.Append(value.ToString());
}
else if (prop.PropertyType == typeof(long) || prop.PropertyType == typeof(Nullable <long>))
{
sb.Append(value.ToString());
}
else if (prop.PropertyType.IsEnum)
{
sb.Append(Convert.ToInt32(value));
}
else
{
throw new System.Exception("Unknown type in the Hash Comparison.");
}
}
}
return(sb.ToString());
}
