EF - Update multiple rows in database without using foreach loop

Just to update Steve's answer, in newer EF (current EF Core 3.1.3) you can do it all as one statement.

await db.Message.Where(m => m.FromUser == fromUser && m.ToUser == toUser).ForEachAsync(m => m.IsRead = true);
await db.SaveChangesAsync().ConfigureAwait(false);

You don't need to SaveChanges() on each iteration. That will hit the database multiple times. Try:

using (var db = new MyDbContext())
{
  string fromUser = ""; //sender
  string toUser = ""; //receiver
  var messages = db.Message.Where(x => x.FromUser == fromUser && x.ToUser == toUser)
                 .ToList();
  messages.ForEach(m => m.IsRead = true);
  db.SaveChanges();
}