C# Reflection - merge two objects together

Question

I have a need to update object A\'s property if null with that from object B\'s equivalent property if that is not null. I wanted code I can use for various objects.

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Answer 1

Hi I modified Ben Robinsons solution in order to not overwrite Collections or list, instead, it adds the elements of one object to the other one where the merging is happening:

 public static class ExtensionMethods
{
    public static TEntity CopyTo<TEntity>(this TEntity OriginalEntity, TEntity EntityToMergeOn)
    {
        PropertyInfo[] oProperties = OriginalEntity.GetType().GetProperties();

        foreach (PropertyInfo CurrentProperty in oProperties.Where(p => p.CanWrite))
        {
            var originalValue = CurrentProperty.GetValue(EntityToMergeOn);

            if (originalValue != null)
            {
                IListLogic<TEntity>(OriginalEntity, CurrentProperty, originalValue);
            }
            else
            {
                var value = CurrentProperty.GetValue(OriginalEntity, null);
                CurrentProperty.SetValue(EntityToMergeOn, value, null);
            }
        }

        return OriginalEntity;
    }

    private static void IListLogic<TEntity>(TEntity OriginalEntity, PropertyInfo CurrentProperty, object originalValue)
    {
        if (originalValue is IList)
        {
            var tempList = (originalValue as IList);
            var existingList = CurrentProperty.GetValue(OriginalEntity) as IList;

            foreach (var item in tempList)
            {
                existingList.Add(item);
            }

        }
    }
}

Answer 2

I have created the below extension method for use in my latest project and it works fine, collections and all. It is a pretty much a simpler version of what you are doing in your method. With mine both classes have to be the same type. What problem do you encounter with collections?

    public static class ExtensionMethods
    {
        public static TEntity CopyTo<TEntity>(this TEntity OriginalEntity, TEntity NewEntity)
        {
            PropertyInfo[] oProperties = OriginalEntity.GetType().GetProperties();

            foreach (PropertyInfo CurrentProperty in oProperties.Where(p => p.CanWrite))
            {
                if (CurrentProperty.GetValue(NewEntity, null) != null)
                {
                    CurrentProperty.SetValue(OriginalEntity, CurrentProperty.GetValue(NewEntity, null), null);
                }
            }

            return OriginalEntity;
        }
    }