I have a super annoying issue where this is the process:

  1. User fills in form
  2. My application uses CSOM to get a list of users from the form (these are selected by the user with people picker - I also want the Author)
  3. I need to add these users to some groups, and here is the problem..

The ListItem user fields are returning FieldUserValues rather than User objects - and these don't contain the user's login name, so how am I supposed to add that user to a group?

It seems ridiculous that I have to write some query using the user's lookup ID, can't I just pass in the FieldUserValue to a group creation method? The only way I have found is to pass in the UPN of the user.

Please can someone help it is so frustrating dealing with this system.

2 Answers 2


You can use the web.EnsureUser method to get the user object. In the method, pass the LookupValue.

Try and modify the below sample code:

FieldUserValue[] fuv = (FieldUserValue[])listItem["UserField"]; 
for (int i = 0; i < fuv.Length; i++) 
    User user = clientContext.Web.EnsureUser(fuv[i].LookupValue); 

    // code to add user to group
    // get the group    

    var group = clientContext.Web.SiteGroups.GetByName("Group name");


  • Thanks Gautam, that is what I ended up doing. However there were extra complications as this org seems to on-prem as well as cloud SP
    – Bassie
    Commented Jun 7, 2018 at 0:13

As Gautam mentioned, I can do this by using EnsureUser

However, what I came to realise was that my organisation seems to have 2 SharePoint instances - a 365 version as well as what I think is a on-premises version.

Therefore, before calling EnsureUser I need to make sure that the ClientContext is pointing at the correct instance.


If I use ClientContext("OnPrem.Company.com"), then the user's LoginName is given as domain\user.name, but if I use Clientcontext("Company.SharePoint.com"), then the username is given as [email protected], which is the actualy selection I want to use when adding the user to a group and when storing the username in the DB

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