Actions and Multiselect
Reposted from Chris Webb's blog with the author's permission.
At the beginning of this week a customer asked me why, in a certain third-party client tool that shall remain nameless, they could no longer do a drillthrough when they did a multiselect on a filter axis. It seemed a bit weird to me, and it got weirder when I asked around for ideas and Greg Galloway pointed out that Excel 2007 didn’t show any actions at all when there was a multiselect, and Marco Russo noted that the current beta of Excel 2010 didn’t either. This made me wonder whether the problem was in fact with Analysis Services rather than the client tools…
I didn’t actually know how a client tool worked out what actions were available when, so I did some research and found out that the MDSCHEMA_ACTIONS schema rowset was how it was done. Here’s the documentation on MSDN:
For example, if a client tool needs to know which actions can be called when a user clicks on a cell in a resultset, then it will execute an XMLA command something like this one on Adventure Works:
You can see that a tuple is being passed into the COORDINATE to indicate which cell we’re interested in. But when there’s a multiselect, which cell in the cube are we actually clicking on? Good question… Different client tools handle multiselect in different ways, and it turns out there’s no way of telling SSAS you’re doing a multiselect in this situation. If you try to pass a set of tuples to the COORDINATE you get no actions returned, for instance.
Having talked this over with Akshai Mirchandani from the dev team, what the client tool needs to do is to make multiple calls to MDSCHEMA_ACTIONS, one for each member selected in the multiselect. It then needs to work out from each of the rowsets returned which actions should be available in the current context – and of course, in this case, there’s a good chance that different client tools will do different things (if they do anything at all). Not ideal.
To be honest, this really needs to be something that is solved in SSAS rather than on the client and the key to solving it properly would be to have a standard way of handling and detecting multiselect in MDX. As Mosha hinted here, it’s something that’s been on the dev team’s radar for a while but it’s still not made it into the product unfortunately. In the meantime, if there are any client tool developers from the Excel team or third parties out there reading this, it would be great if you could at least do something rather than nothing here!
Chris has been working with Microsoft BI tools since he started using beta 3 of OLAP Services back in the late 90s. Since then he has worked with Analysis Services in a number of roles (including three years spent with Microsoft Consulting Services) and he is now an independent consultant specialising in complex MDX, Analysis Services cube design and Analysis Services query performance problems. His company website can be found at http://www.crossjoin.co.uk and his blog can be found at http://cwebbbi.spaces.live.com/ .