I have a list lookup that is currently reading a list inside my sharepoint environment. All is well. However, I've been told the data that this list will need to change over to a external list so it can be viewable from multiple sharepoint sites and it can be updated from one location. Essentially removing the need to update the list in three different sites. Made sense to me, until I tried to change the location of my list lookup to point to the new external list. It doesn't show up in the drop down for the source list. I've searched around and seen a handful of posts, but with no real solutions (some of them are quite old too). I've tried to change the Source List to an expression then list the name external list name. That doesn't save when I try that. Has anyone been able to get this to work? I know I can use the SQL controls to effectively get what I need. However, that will effectively cause all my previous forms to lose information. Deleting that control and inserting the SQL control could cause me other headaches. Is there no way to point the list lookup to an external list?
Use a List Lookup control to query a External List
Ok, a little more information here. We were able to successfully use the list lookup control to poll the external list. Following @igorsp post https://community.nintex.com/t5/Nintex-for-SharePoint/Display-lookup-info-from-an-external-list/td-p/11839, I was able to get the control to successfully poll the list and be able to select the item. However, as he mentions in this post, I am unable to use the lookup function as part of a calculated control to poll information in that same list. As this post is a few years old, I was wondering if someone else has found a solution to this.
Ok, after working with support we still could not discover a solution and they could not definitively tell me if the lookup function works with external lists. At this point, I'm under the impression it is not possible. I ended up changing the control to a sql control and parsed the data from sql database the external list was referencing. This presented a challenge as my form's various calculated fields were pulling data from the original control. Since the control is now different, I had to create a new formula for each control. Since I had the controls set to only evaluate in New and Edit modes, Display mode the user see's no issue. In most cases, my users will not go back into edit the form after it is approved. There would be no reason to do so (this is a purchase request form). In the off chance someone actually does go into edit mode, they only need to re-select the vendor.
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