-Re: Composite key, scan on partial key
Bryan Keller 2010-12-15, 01:32
Isn't a filter much less efficient than specifying a range with the Scan object?
On Dec 14, 2010, at 3:32 PM, Ryan Rawson wrote:
> If the order ids are variable, then you will have to use a separator.
> You then can use a start of 'foo:' and a prefix filter of 'foo:'.
> The start,end key wont work with variable length in this way. But the
> good news is prefix filter is very efficient.
> Good luck!
> On Tue, Dec 14, 2010 at 3:28 PM, Bryan Keller <[EMAIL PROTECTED]> wrote:
>> I had a question about using a Scan on part of a composite key. Say I have order line item rows, and the ID is order ID + line item ID. Each ID is a random string. I want to get all line items for an order with my Scan object.
>> Setting the startRow on Scan is easy enough, just set it to the order ID and leave off the line item ID. However, because endRow is exclusive, I need to come up with a key that is just past the order ID. This would be straightforward if the keys are numeric (just add one to the order ID), but becomes kind of a kludge when the keys are strings.
>> Right now I build the keys with a byte separator between the two strings and set it to 0 when storing. Then when I want to scan, I create the startRow with the Order ID + (byte)0, and the endRow with Order ID + (byte)1. Seems like kind of a waste to have that extra byte just for this purpose, though. Is there a better approach, like specifying the endRow inclusively?