Populate SiteColumn type choice field with List Items

Question

I am building a SP app in VS2012 and need a content type field to show a dropdown choice list with items from a list within the app itself. To keep thing simple:

• List1 has a FieldX column with values A, B and C. But this might become more values or less values once the app is in use.
• DocLib1 is a document library which uses a obligatory ContentType1. FieldX is a field in ContentType1 and when adding a document to DocLib1 the user should have dropdownlist A, B, C values to choose from (or whatever values are in FieldX column of List1 at that moment.

How can I achieve this? I really have no clue where to start.... All help will be highly appreciated!!!

Edit: I found a way to read the items in a variable with javascript, but don't know how to insert them as choices in the Site Column I created in my custom Content Type. Is there a way to write them to the Elements.xml file tags somehow?

Answer 1

If I understand it right, you could create a LookupField in your DocLib1 which shows the values of FieldX Column from List1?

Reference to Lookup Columns: http://office.microsoft.com/en-us/sharepoint-server-help/create-list-relationships-by-using-unique-and-lookup-columns-HA101729901.aspx