Recently I posted about accessing lookup fields in item event receivers and about some pitfalls when you are using it.
Next part is about using PeopleEditor (or people picker as it sometimes called). Let's add new field to our list and see what will happen in event receivers.
In AfterProperties you can see "7". "7"?! Why? Because SPFieldUser that we was added also an a lookup field. Lookup list for this field is a hidden UserInformationList that trackes a part of user-related information, such as login name, display name, email, and some other. "7" is id of user in UserInformationList. You can get SPUser object by using method web.SiteUsers.GetByID(id), or you can use SPFieldUserValue to get user.
In ItemAdded you can see that our lookup has a value - this a login name of a user:
But sometimes you may encounter with problem, when user may not in UserInformationList. I delete user from this list using this small PS script:
Recently I was playing with synchronous item event receivers and lookup fields and found some interesting behavior in different situations. I'll try to describe some pitfalls that I faced when develop item receivers for SharePoint.
So, lookup fields. When you try access to a lookup field in such events as Adding or Updating you may to have lookup value. But AfterProperties always contain only lookup Id, if you want to get lookup value you must query item by id. Imagine you have a list named "Software", it has title field and category lookup field (now we have 19 category types in "Category" list). When we try to add new item in "Software" list in ItemAdding event we can see:
Where "18" is an Id of category. And ItemAdded:
So, when use class SPFieldLookupValue, in ItemAdding event LookupValue equal to null (in AfterProperties) and not null in ItemAdded(in ListItem).
Let's try to update this item:
Situation is very similar - in AfterProperties we have an item Id (LookupId in SPFieldLookupValue class, LookupValue is null), and value in ListItem. In ItemUpdated event as you may know we will have both lookupId and LookupValue. Be aware of this SharePoint behavior.