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Implement the grpc-server method AddItemAndOrder: 1. Add items to the cart 2. Be sure to notify potential consumers about the cart checkout via a message broker. 3. When the cart contents change, recalculate basket.Total = sum(count * price) 4. All cart items must be unique by the ProductID key 5. To checkout the cart, change its status to ordered 6. No changes are allowed to finalized carts There is a table where all columns are integers. The code contains the query: select * from t1 where a > ? and b = ? and c != ? order by a;

sobes.tech AI

Answer from AI

Below is an example implementation of the gRPC server method AddItemAndOrder in Go, which considers all requirements:

func (s *Server) AddItemAndOrder(ctx context.Context, req *pb.AddItemAndOrderRequest) (*pb.AddItemAndOrderResponse, error) {
    basketID := req.GetBasketId()
    newItems := req.GetItems() // list of items to add

    // Retrieve basket from database
    basket, err := s.store.GetBasket(ctx, basketID)
    if err != nil {
        return nil, err
    }

    if basket.Status == "ordered" {
        return nil, status.Errorf(codes.FailedPrecondition, "Cannot modify an ordered basket")
    }

    // Create a map for uniqueness by ProductID
    itemsMap := make(map[int32]*pb.Item)
    for _, item := range basket.Items {
        itemsMap[item.ProductId] = item
    }

    // Add/update items
    for _, newItem := range newItems {
        itemsMap[newItem.ProductId] = newItem
    }

    // Recalculate total
    var total int32 = 0
    var updatedItems []*pb.Item
    for _, item := range itemsMap {
        total += item.Count * item.Price
        updatedItems = append(updatedItems, item)
    }

    // Update basket
    basket.Items = updatedItems
    basket.Total = total

    // Change status to "ordered" if the request has the order flag
    if req.GetOrder() {
        basket.Status = "ordered"
    }

    // Save changes
    err = s.store.UpdateBasket(ctx, basket)
    if err != nil {
        return nil, err
    }

    // If the basket is ordered, publish an event to the message broker
    if basket.Status == "ordered" {
        err = s.messageBroker.Publish("basket_ordered", basket)
        if err != nil {
            return nil, err
        }
    }

    return &pb.AddItemAndOrderResponse{Basket: basket}, nil
}

In this example:

All items are unique by ProductID thanks to the itemsMap.
When the basket composition changes, the Total is recalculated.
The status changes to ordered upon checkout.
Modifications to an ordered basket are prohibited.
After checkout, an event is published to the message broker.

Regarding the SQL query:

select * from t1 where a > ? and b = ? and c != ? order by a;

This is an example of a parameterized query, where ? are placeholders for values. This approach helps prevent SQL injection and improves code readability.

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