The iterative design process: Query parameters example
When we start building a feature, we often have a pretty good idea of what we want to have and how to get there. And then we actually start building it and we often end up with something that is quite different (and usually much better). It has gotten to the point where we aren’t even trying to do hard specs and detailed design at anything beyond the exploratory levels. For example, in the design of RavenDB 4.0, there was not even a mention of RQL. That ended up being a very late addition to the codebase, but it improved RavenDB significantly. On the other hand, the low level mechanisms of zero copy documents from Voron all the way to the network were designed up front, but only at a fairly high level.
In this post, I want to talk about query parameters in RavenDB. Actually, let me be more specific, we have query parameters, but what we don’t have (or rather, didn’t have, because that will be merged in by the time you read this post) is the ability to run parameterized queries from the studio. We always meant to have that capability, but we run out of time with the 4.0 release. As we are gearing up to the 4.1 release, we are cleaning the table from the major-minor issues. (Major in term of impact, minor in term of amount of work required). The query parameters in the studio is one such example. Here is what this looks like:
My first thought was to just build something like this:
Give the user the ability to define arguments and be done with it. The task was assigned to one of our developers and I expected to get a PR in a short while.
This particular developer has a tendency to consider not just the task at hand but also other aspects of the problem. He didn’t want the user to have to manually specify each argument, since that has poor ergonomics. Instead, he wanted the studio to figure it out its own and help the user. So the first thing he did was detect the arguments (regex: “\$\w+”) and present them in the grid. Then there was the issue of how to deal with edits, etc. Then he run into another problem, types. Query parameters can be more than just strings, they can be any JSON data type.
Here is what he came up with:
Instead of having to define the query parameters in a separate location, just put them right in. Having the parameters grid involves pointing and clicking with the mouse, entering possibly complex values (such as long arrays) and in general much more work than just having them right above the query.
Note that this is a studio only feature, queries from the client API already have ways to specify arguments properly. So the next question is how we are going to handle passing the arguments to the server. Remember, this is only on the studio, so we can take quite a few shortcuts. In this case, we’ll simply snip the entire first section of the query text (which contains the query parameters). We can do that by going from the start of the query to the first from or declare keywords. We do a basic pre-processing to turn “$name = …“ into “results.$name = …“ and then just execute this code in the browser, giving us a JS object with all the parameters that we can then send to the servers.
The next stage is to make this discoverable, by detecting parameters whose value is not provided and giving the user a quick fix to add them.