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Updating an object with MVC

When editing an object (like an entity) in MVC, it returns a new one populated with your objects. If you try to save it using dataContext.Attach(), you may find that when saving it bombs on you. A great example of this would be something like a DateTime called .CreatedOn, since you wouldn’t let users edit it, would be the same value as new DateTime() which is year 0 or 1. When the object attempts to be persisted it won’t allow a date that low to be stored in a normal datetime field in SQL (datetime2, yes, but datetime should be sufficient in most cases) and bombs with a YSOD.

Maybe there’s a better way, but until I discover it or someone points it out to me, here’s what I did:

/// <summary>
/// Maps only the submitted changes in model state from one object to another.
/// </summary>
/// <typeparam name="T"></typeparam>
/// <param name="mapToObject"></param>
/// <param name="mapFromObject"></param>
public static void MapChangedProperties<T>(this ModelStateDictionary modelState, ref T mapToObject, T mapFromObject)
{
	var props = typeof(T).GetProperties();
	foreach (var item in modelState)
	{
		var prop = props.FirstOrDefault(p => p.Name == item.Key);
		if (prop != null)
		{
			prop.SetValue(mapToObject, prop.GetValue(mapFromObject, null), null);
		}
	}
}

To use, get the object out of the database and run this on it:

// "obj" is our returned model name, and we have a database connection open
if (ModelState.IsValid)
{
        dbObj = db.Objs.Single(o => o.ID = obj.ID);
        ModelState.MapChangedProperties(ref dbObj, obj);
        dbObj.ModifiedDT = DateTime.UtcNow;
        db.SaveChanges();
}

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