Considerations and Best Practices for extending Content Types in Atlas

When extending Content Types in Atlas there is a specific process you need to follow to ensure the extensions work correctly, which is explained here: Content Type Extensions Utility

However there are also a number of limits on extensions coming from Microsoft in terms of number of Lookup columns in a List view and the number of Mandatory Lookup columns in a list (regardless of whether they are shown in views). These limits are not actively enforced, so it is possible to break your list views by adding too many Lookup columns if not planned carefully.

This article explains these Microsoft limits.

Microsoft Lookup Column Limit

Microsoft have a limit of how many lookup columns you can have (these include People columns and Managed Metadata columns as well as actual Lookup columns to other lists).

It is generally understood in the SharePoint community that having more than 12 Lookup columns showing on a list or library view will break the view and prevent it being displayed. However, a less known fact is that Required Lookup columns (e.g. set as a Required column in the list) are included in this limit whether they are shown in the view or not - we suspect this is because they need to be loaded for the form displayed for the "New" button.

Therefore if you have more than 12 Lookup columns in a list or library the process needs to be managed carefully. Since Atlas content types already include 9 or 10 Required Lookup fields depending on which content type, you may only be able to add 2 or 3 Required Lookup fields, so some of your extensions may need to be set as Optional to avoid breaking the views.

Why is this important?

Atlas content types include 5 or 6 mandatory lookup fields out-of-the-box (5 global - Activity, Department, Entity, Location, Subject;  and sometimes a "Type" dependent on the content type).

Microsoft OOTB libraries include 4 mandatory lookup fields (Created, Created By, Modified, Modified By)

Atlas has other optional lookup columns (3x author fields), and Microsoft has other optional lookup columns which might be in play depending on content type. 

So if you're adding more Lookup columns it is very likely you will hit the 12 limit if you want all of them to either be mandatory (required), or to be shown in a list/library view.

Microsoft have very little documentation on this limit, even the number 12 is not actually stated in documentation. So these rules and guidelines are something ClearPeople have had to discover, manage, and strategise accordingly - so they are a common pitfall when creating custom content types that have numerous lookup columns.

Our advice

We advise that if you are looking to do some advanced content type configuration, please get in touch with your Atlas Representative so we can discuss and properly plan out the steps and architecture so we can leverage all of our experience to avoid problems and progress smoothly.