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Product Advertising API
Developer Guide (API Version 2013-08-01)

Specifying the Items in the CartCreate Request

In one CartCreate request, you can add up to ten different items to the cart. The quantity of each item can be between 1 and 50. That means in one CartCreate request, you could add up to five-hundred items (10 items * 50 quantity).

Items are specified in parameter pairs, as follows:

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Item.N.ItemIdType=[Item identifier] Item.N.Quantity=[Number of Item.N items]

N is a positive integer. The N value associates the ItemId with the quantity of those items that should be added to the cart, for example:

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Item.1.OfferListingId=[An OfferListingId]& Item.1.Quantity=3& Item.2.OfferListingId=[An OfferListingId]& Item.2.Quantity=5&

This request adds three number 1 items and five number 2 items to the remote shopping cart. You could interchange lines without affecting the end result, for example:

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Item.1.OfferListingId=[An OfferListingId]& Item.2.OfferListingId=[An OfferListingId]& Item.1.Quantity=3& Item.2.Quantity=5&

The values for N do not have to be listed in ascending or descending order, nor do the values of N need to be sequential. You could, for example, use the values, 1, 4, 7 for N. Also, the value of N is not retained between requests. For that reason, it is permissible to use Item.1 in a CartCreate request and then in a CartAdd request, which adds an item to the cart. In these requests, Item.1 can refer to two completely different items.

The value of adding multiple items to the cart in one request is performance. It takes less time to add ten items in one request than it does to add ten items to the cart in ten separate requests.

Using OfferListingId

You can specify items to add to a cart in the following ways.

Identifiers Description
ASIN An alphanumeric token that uniquely identifies an item sold by Amazon. Amazon assigns ASINs to items. Using OfferListingId is the preferred method of identifying items to add to the cart.
OfferListingId An alphanumeric token that uniquely identifies an item sold by a seller or merchant. Amazon assigns OfferListingIds to items. You can find an OfferListingId using the ItemLookup and ItemSearch operations with Offers and OfferFull response groups. Using OfferListingId is the preferred method of identifying items to add to the cart.

The CartCreate example uses OfferListingId to identify the items to add to the cart. An OfferListingId is returned by the Offers and OfferFull response groups. An alternative is using an item's ASIN. An ASIN is assigned to every item offered by Amazon. An OfferListingId is assigned to every item that is available for sale.

The advantage of using OfferListingId in the CartCreate request is that items that cannot be purchased, such as Variation parent items, do not have OfferListingId's. By using the OfferListingId, you are assured that an item can be purchased.

Offers and Identifiers

ASINs identify items, such as a Harry Potter book. ASINs do not, however, identify sales information related to those items.

As you can see in the preceding figure, an ASIN identifies an item but not an instance of it that a customer can purchase. Every ASIN can be sold by many merchants. Each merchant lists the condition and price of the item. This combination of data represents an OfferListingId. Taken together, all OfferListingIds are referred to as offers. If an ASIN does not have an OfferListingId, the item cannot be purchased.

For this reason, it is recommended that you add items to a shopping cart by their OfferListingId rather than by their ASIN.