✅ I want to get duplicate items in my List (EF Core)

var deckList = await _context.DeckContents
            .Where(i => i.DeckId.ToString() == deckId)
            .Select(i => i.CardId)
            .ToListAsync();

var cardList = await _context.Cards
            .Where(i => deckList.Contains(i.Id))
            .ToListAsync();