Recently, we came across a severe problem in production farm with the Content Types. I would like to explain the background of this problem first.
We have nice working feature for Content Types installation in production and test farms. We developed and deployed (using wsps) this SharePoint feature in Visual studio. We are using the publishing pages using page layouts and Content Types to help content editors to quickly publish the web pages. Unfortunately, some Content Types and site columns have been manually updated/added by some people in the production, so whenever I (developer) make some changes to the existing Content Types (using Visual Studio and feature activation/deactivation) , SharePoint removes one or two columns (during feature activation/deactivation) from Content Types; or the columns which have not been added in a best practice way. I think the best practice is to update Content Types using Visual Studio.
Now, I wish to ensure that site columns shouldn’t get removed from Content Types upon feature activation/deactivation.
Note: Our feature for Content Type activation/deactivation doesn’t hold any activation dependencies in the feature.xml
Recommended Approach
Based on all these factors, my suggestion would be to:
• Create two Features: one for the original markup and one for making changes. (Or you can put them in the same Feature; I just want to differentiate between where you do what.)
• The original Feature should contain the CAML for Site Columns and Content Types. This ensures the IDs have been assigned ahead of type and remain constant.
• If you want to update a Site Column by changing nearly anything about it except its Field type, do it using a Feature Receiver. By doing this, you can call the Update method and pass in a boolean indicating if you want all the existing assets in the site that inherit from this to update to, (something you couldn’t do via the CAML.)
• You can also add an existing Site Column (that you provisioned via the CAML feature) to an existing Content Type (that was provisioned via the CAML feature). This is helpful if the Column was not part of that Content Type before, etc.
• In a scenario like the one I just mentioned in the last bullet point, it’s necessary to deactivate and reactive the CAML feature (to provision the new assets) before calling your Feature Receiver. What will this mean for the site? Since all the Site Columns and Content Types in the lists in the site are using the same ID’s as the ones provisioned in the Site Collection root, removing its parent from the Site Collection won’t change that. It might leave it orphaned temporarily, (i.e. there will be no relationship between that item and an item in the Site Collection root, but it will function the same way it always has, since it’s really a fully-functioning copy of the original item) until you reactivate the Feature that puts the item back in the Site Collection. It’s like the parents are going on vacation when you deactivate the Feature, and are coming back home when you activate the Feature again.
You have a choice when it comes to how you maintain the CAML and the Feature Receiver, since you have two scenarios: existing Site Collections and new ones.
• You could make a policy that every time you write code in your Feature Receiver to update a Site Column or Content Type, you have to make the change in your CAML as well. That would mean that every time you activated the CAML Feature in a “fresh” Site Collection, the CAML would be up-to-date and accurate; there would be no need to run the “updater” feature. (In your Feature Receiver, you should make sure you do some extra checking to make sure a Site Column doesn’t already belong to a Content Type before adding it, etc. in case that change is already in place before the code executes.) This approach means you only have to execute one Feature when creating a new Site Collection, but it also means you’re maintaining changes in two places: in your Feature Receiver for making changes to existing sites, and in your CAML for new sites. It’s a cleaner approach, but also contains an element of redundancy, which always leaves room for human error.
• The other approach is to simply assume that every time the base CAML feature is activated, you’re always going to execute the Feature Receiver. This approach says the only time you’d change the CAML is to add a new Site Column or new Content Type; otherwise, all the changes happen in the Feature Receiver. This approach reduces redundancy, but also means your Feature Receiver code could get quite large with all your changes over time, and it could leave your CAML as very much “legacy” over time.
Src: http://blog.beckybertram.com/Lists/Posts/Post.aspx?List=eb3e1762%2Dbab0%2D4e96%2D8bc5%2Dd67d6e6bfd44&ID=18