Aug 14, 2020 03:01 AM|yij sun|LINK
Accroding to your description,as far as I think,you could update them one-by-one in a Foreach.Then you could call SaveChanges().
More details,you could refer to below codes:
WallPaperCategory std = (from x in Context.WallPaperCategries
where .... // add where condition here
foreach (WallPaperCategory x in std )
x.is_default = false;
More details,you could refer to below article: