For example this item 293207269018 comes in multiple shirt sizes. 1. How do I know how many variations does an item have? Can I find it with Finding API, shopping API? 2. Where do I find the values for the various variations? for example, I want to present a bomber jacket. but their price, color, size, may vary, and all are under one listing ID. How can I approach this in order to fetch data so later I can organize it in my DB?
Trading requires headers and a token. There are ways to send the requests using header manipulation browser add-ons, but you still need to fetch the token. When you do a Finding request, each variation is returned as a separate item unless you set HideDuplicateItems. But Finding does not return the values themselves with each item. You can use findItemsAdvanced with the outputSelector=AspectHistogram which will return a node containing all the ItemSpecifics/Aspects. You can then do another call and request only the items that match certain aspects. This is useful if you want to find many items of a particular size/color/etc. Use Shopping GetMultipleItems to retrieve the variation details by itemID. It returns a single item node per item, with a variations node listing each variation's details. This is useful if you want to show all the variations of a particular item. Finding returns a flag for variation items, so you can use that to determine when to call Shopping if you want to combine the two. <isMultiVariationListing>true</isMultiVariationListing>
Trading was intended for sellers and has access to more data if you are the seller or the buyer. So if you need addl info about items you are selling, use Trading. Support here tends to default to GetItem for some reason in all their responses about item data. Finding and Shopping give you most of the data you'd want for websites/apps. The Buy/Sell APIs have additional hoops to jump thru to get the same information.
I'm not very familiar with trading API - Do I have have to submit a separate query per every product ID? If so, this is very inefficient. what If I want to query thousands of items, and each of them has variations? I get a list of results from finding API with one call, and then need to go one by one on any product that is "multivariation = true" with a separate trading call? Also, is there a way to send and get a trading response via Browser, like with Finding and Shopping? And in which case do variations appear within the Finding API response itself? I remember some instances of getting same item ID in response, which means they are listed as variations, but I cannot re-create this.