C# - Get property in member class using Reflection

SHORT VERSION

What's the best way to use reflection to turn something like string prop = "part1.first_name"; into a System.Reflection.PropertyInfo, so that I can use the GetValue and SetValue functions?

LONG VERSION

I'm using ASP .NET MVC to build a questionnaire for my organization. It's very long, so it's divided into several different pages. Since it's not uncommon for us to get requests like, "Can you move this question to that page, and this other question to another page," I need to build this to be pretty flexible for a junior programmer to change.

My model is a complex class (it's got five member classes that have mostly primitive-typed properties on them).

So, I access it by doing things like Model.part1.first_name or Model.part2.birth_date.

Since the same model is used on all of the pages, but not all of the questions are on every page, I have ActionAttributes that essentially clear out all of the properties that were submitted on the form except for the ones that were displayed on that page (so someone can't inject a hidden field into the form and have the value persist to the database).

I want to make sure that I only save valid field values and don't let the user proceed to the next page until the current one is entirely OK, but I also want to save the values that are valid, even if the user isn't allowed to proceed.

To do this, I have a function that takes two instances of my model class, a reference to the ModelState开发者_JAVA百科Dictionary, and a string[] of field names like "part1.first_name" and "part2.birth_date". That function needs to copy all of the values listed in the string array that do not have validation errors from the first (ie, form-submitted) object into the second (ie, loaded from the db) object.

As stated above, what's the best way to use reflection to turn something like "part1.first_name" into a System.Reflection.PropertyInfo, OR, is there a better way to accomplish this?

---

var infoParts = prop.Split('.');
var myType = Type.GetType(infoParts[0]);
var myPropertyInfo = myType.GetProperty(infoParts[1]);

Assuming "part1" is your type. Although this is very limited and very dependent on the string being in the correct format and the type being in the current scope.

---

I would probably handle this differently, using data. I would keep, in the database, which step each question belongs to. To render that step, I would select the questions that match that step and have a model that contains a list of question id/question pairs. Each input would be identified by the question id when posted back. To validate, simply compare the set of question ids with the expected ids for that step. This way, to change which question goes in which step is to only change the data in the database.

If you do end up going down that road, you'll need to split the string into parts and recursively or iteratively find the property on the object at each step.

PropertyInfo property = null;
Type type = questionModel.GetType();
object value = questionModel;
object previousObj = null;
foreach (var part in questionId.Split('.'))
{
    property = type.GetProperty(part);
    previousObj = value;
    value = property.GetValue(value,null);
    type = value.GetType();
}
// here, if all goes well, property should contain the correct PropertyInfo and
// value should contain that property's value...and previousObj should contain
// the object that the property references, without which it won't do you much good.