Fetching multiple SimpleDB items in a single request
The only way to retrieve multiple items at a time, along with their attributes, from Amazon SimpleDB is with the Select operation. Typically, you query for some property of the items which you want to retrieve, not by item name:
select * from my_domain where date > '2009-01-01'
The only documented way to retrieve the attributes of an item by item name is with the GetAttributes operation, which only gets one item at a time. But what if you have a list of item names you want to retrieve, and you just want to avoid the overhead of making a separate GetAttributes call for each one?
A clue towards the solution can be found in the fact that the special itemName() token can be used in the field list for Select:
select itemName() from my_domain where date > '2009-01-01'
I didn't find this explicitly documented anywhere, but you can also use itemName() in a query condition:
select * from my_domain where itemName() = 'ABC123'
…and from there it’s a short step to our solution, which uses the IN predicate:
select * from my_domain where itemName() in ('ABC123', 'DEF456', ...)
And there you have it, a way to retrieve multiple items by name in a single request, subject only to limits on query size and response size. I don’t know if this is common knowledge to longtime SimpleDB users, but it was new to me, so I thought I’d share it.
This work, unless otherwise expressly stated, is licensed under a Creative Commons Attribution-Noncommercial-Share Alike 3.0 United States License.
Related posts:
