Get Principal By Id - Getting User or Group by ID

Question

How to get a CSOM Principal from a user or group ID?

For example to assign permissions stored in a "People" field (which can also contain groups).

At the moment I have this super kludge using ExceptionHandlingScope.

void AddRole(SecurableObject securable, int principalId, RoleDefinition role)
{
    var scope = new ExceptionHandlingScope(context);
    using (scope.StartScope())
    {
        using (scope.StartTry())
        {
            var principal = context.Web.SiteUsers.GetById(principalId);
            securable.RoleAssignments.Add(principal, new RoleDefinitionBindingCollection(context) { role });
        }
        using (scope.StartCatch())
        {
            var principal = context.Web.SiteGroups.GetById(principalId);
            securable.RoleAssignments.Add(principal, new RoleDefinitionBindingCollection(context) { role });
        }
    }
}

The REST API just accepts raw principal ID, but that loses a lot of the advantages of using the CSOM.

Answer 1

You can use the ResolvePrincipal method in the Microsoft.SharePoint.Client.Utilities namespace.

It accepts the principal ID, but you need to send it as string instead of int. Also, instead of ID, if you directly want to send the user's or group's name, it would work

It would work as below:

using Microsoft.SharePoint.Client;    
using Microsoft.SharePoint.Client.Utilities;

void AddRole(SecurableObject securable, int principalId, RoleDefinition role)
{       
    var info = Utility.ResolvePrincipal(context, context.Web, principalId.ToString(), PrincipalType.All, PrincipalSource.All, null, false);

    context.ExecuteQuery();

    Principal principal = null;

    if (info.Value.PrincipalType == PrincipalType.User)
    {
        principal = context.Web.SiteUsers.GetById(principalId);
    }
    else if (info.Value.PrincipalType == PrincipalType.SharePointGroup
          || info.Value.PrincipalType == PrincipalType.SecurityGroup)
    {
        principal = Context.Web.SiteGroups.GetById(info.Value.PrincipalId);
    }
    else
    {
        throw new NotImplementedException($"PrincipalType {info.Value.PrincipalType}");
    }

    securable.RoleAssignments.Add(result, new RoleDefinitionBindingCollection(context) { role });
}

Modified from here - ResolvePrincipal vs SearchPrincipal