Add/Remove user from group when user is / is not a member already

Question

I am working with updating groups programmatically and have been wondering how SPGroup's react when you:

a) Try to remove people that are not already a member - silently fail, throw exception, ??
b) Try to add a person to a group he is already a member of - again, with what outcome.

Since MSDN do not document Exception-handling (at all) I tried google but I can't seem to find any articles with my google-fu that will give me the right answer.

Any and all help is appreciated.

Answer 1

In both cases nothing will happen because there is nothing to do on SPGroup.Update(). If you are trying to add user that already exist - it's already there and if you are trying to remove user who is not member of group - there is nothing to remove.

Your code will continue as normal and no exception will be thrown.

I personally find this 'malfunction' to be very useful especially in case where you are programmatically doing bulk SPGroup updates.

Answer 2

I can only provide anacdotal evidence to this question. In some Nintex workflows we have, we are adding users to groups via the web services. When a user is already in the group, the workflow continues on, the workflow does not error. I haven't tried to decipher if it is readding the user or if it is just aborting and silently continuing because the user is there.

I have not tried to remove users from a group via the web services in a workflow so I don't have any evidence to give you on that.