Welcome to my first post on my SharePoint Blog. In this post we will talk about
using Business Connectivity Services in SharePoint 2010. If you are thinking
that this post is about introduction to BCS or its advantages then let me tell
you it is not, this blog is about the commonly faced challenges while working
with BCS. If you are new to BCS i would suggest you to go through
this wonderful article about BCS. So lets get
started!
Lets assume that by now you understand BCS and you have already created an
external content type and an external list. Now as a developer the first thing
that comes to my mind is i have a list ready can i use it like any other
SPList? Unfortunately the answer is No.
Here are the list of challenges i faces while exploring an external list
created using BCS
Challenge1: Permission denied to view the contents of external list on
UI.
Possible Reason : You have not set the permissions on BCS entity.
Solution: In Central Admin go to Application Management, then Manage
Service Applications. Open the Business Data Connectivity Service and select
your entity, then select Set permission from the context menu or click on the
Set Object Permission button. Once you have permission to the entity the error
should go away.
Challenge2: Attaching an event receiver to external list.
Possible Reason: External Lists do not support event receivers
Solution: i created an event receiver in visual studio which would
handle ItemCreated event and attached it to the external list. the code got
deployed without any errors but on creating a new Item in DB or in list the
receiver would never fire. after doing a lot of research i came to this
conclusion that External lists do not support sharepoint event handlers.
However i could not find any conclusive proof for this, hence the conclusion
drawn is on bases of my findings.
Challenge 3: Accessing an external SPList through code
Possible Reason: Usage of 'Pass Through Authentication'
Description: here is one of the most interesting challenges i faced
while working with an external list. i wanted to access and update my external
list throught custom code so i wrote a simple sharepoint code of accessing the
list but as soon as i iterated the ListItemCollection i got the following
exception:
System.UnauthorizedAccessException: Attempted to perform an unauthorized
operation.
at
Microsoft.SharePoint.SPListDataSource.CheckUserIsAuthorized(SPBasePermissions
perms)
Now this clearly indicated
that the identity with which the list was being accessed didn't have
sufficient permission to access the list. I was running the code under elevated
privileges block and the app pool identity had all the required permissions on
SharePoint list, external database and the BCS
entity.
Solution: Here is
what actually happened when i tried to access the list from my code, since i
was accessing an external list which in turn accesses an external database so
my Identity made two hops to get to external database. The first hop was
made from my client machine to the server and the second one from server to
external system. Since BCS uses 'Pass through Authentication' by default
so it does not work with NTLM, as a result of this the second hop i.e from
server to external system the Identity passed was 'Anonymous'.
Here is a wonderful
article which explains this issue in detail and also helps one to understand
the different authentication types used with External system.
The solution to this problem was usage of
'Secure Store' for BCS authentication which solved the double hop problem by
storing the required credentials in SharePoint.
Storing credentials in Secure Store will
enable BCS impersonation and thus the external system can be accessed with
required permissions.
Setting up
BCS with Secure Store Application impersonation
This article describes step
by step procedure to do it.
Hope this
post will be helpful to you all. have fun working with SharePoint!!
