Use SelectMany
instead:
UserSiteMapping = cd.SiteDefinitions.SelectMany(p2 => p2.UserSiteMappings)
You may also need ToList()
or ToArray()
call to switch from IEnumerable<T>
to ICollection<T>
:
UserSiteMapping = cd.SiteDefinitions.SelectMany(p2 => p2.UserSiteMappings).ToList()