Tuesday, January 12, 2010

Hack day with Kenny: Fey::ORM, testing and screen.

After sleeping through the Linux@LAX users group meeting (sorry guys), I rolled up to Kenny's (Kenny Flegal), where he had invited me for a day of coding and authentic Salvadorian food. Win Win!

I showed him briefly the topic of my upcoming Monger's presentation, but mostly we looked at his current project. He is forking a GPL licensed project, to recreate part of the functionality and extend it in a different direction. Along the way he's rewriting the app layer in perl from command line php scripts.

We discussed the various clauses of the Gnu Affero GPL with regards to the hosting of the project during the initial revs. Can he have a public repository before he has finished changing all references to the old name to a new name and adding "prominent notices stating that you modified it, and giving a relevant date" as per Section 5, paragraph a? We decided that he probably could, but that it'd be easier to start with a private repo and not publish until that part is done. That seems sub-optimal from a "getting the source to the people" mindset, but it is more optimal in the "protect the good name of the original project and publishers." For a fork that won't follow up-stream patches, does one just make a single prominent notice to that affect like, "forked from project XYZ on 2010-01-02?"

Along with switching from php to perl, he's pulling out the hard coded sql from the scripts and moving to an ORM. He's picked Dave Rolsky's impressive Fey ORM. This project has a ridiculously complex set of schemas, with inconsistent table names and not explicit foreign key constraints. As such, it is extra work to get the fey schema situated.

Kenny started to give me a run through of some of the code, but it was awkward with both of us on laptops to see the code conveniently. I made him stop and set up a screen session for sharing, as described in my previous post on screen. This was more difficult than I expected, with the problem eventually being that ubuntu 9.4 and beyond has moved /usr/bin/screen to /usr/bin/screen.real and made screen a shell wrapper. The screen multiuser ACL system requires that the screen binary be setuid (chmod +s). With this setup we needed to make screen.real setuid. That took a while to notice.

Once we had a shared session open, it was much easier for him to give me a guided tour of the codebase and database/sql setup. Once that was clear it was time to get some code started. He showed me some of the Fey::ORM model code and how he was migrating over the individual sql statements to the ORM. He had been plugging away on the model code for a while, starting by creating a comment for every line of sql in the application including the file and line of the caller.

The next step was clear, we needed some tests. We set to work getting an initial test of the model code. First we installed Fey::ORM::Mock as a mock layer. This works at a higher level than a standard DBD::Mock interface to allow better testing of the Fey::ORM features. The test didn't pass at first due to missing data in the mock object, so we grabbed a list of the fields that mapped to DB fields and started adding values to pass constraint failures on the data. Once we had a minimal set of data then we started to see problems with the ORM schema description. The lack of well defined foreign key constraints meant we needed to explicitly define that structure for the ORM. More boilerplate code into the model. We repeated this test-update-repeat cycle a few more times adding more data linkage descriptions.

I took a brief break from our pairing and jumped to a different screen to install some goodies. I grabbed a copy of the configuration files from the December la.pm.org talk and started updating his config. He didn't have a .vimrc, .vim or .perltidyrc on this brand new dev box, so I pulled those in from the repo. I showed him how much time using ":make" in vim could slice off his build/test cycle, and he was super excited. (ok, not till the third or fourth try but he eventually got the hang of it).

To get around some issues in code placement, I modified the .vimrc and .vim/ftplugin/compiler code to add -MFindBin::libs to the calls to perl -c and prove. This allowed the parent libs/ directory to be found for these non-installed modules. This is a bit of a hack and I'll get it removed as we move closer to an initial release and pick a packaging tool, possibly Dist::Zilla.

An open question is the speed of Fey::ORM. It takes a big startup hit while building the models from the schema and interacting with the database. This is supposed to lead to a big speed gain during runtime from aggressive caching of that information. All I know for certain is that the compile-run-test cycle was really slow. This is my first time using Fey so I don't know how this plays out normally. It could just be that the number of crosslinked tables in the db config were causing additional slowdowns.

By this point we had already had two delicious meals of El Salvador cuisine and it was approaching midnight. The first meal was home cooked fried (skinless) chicken for lunch and the second was papoosas at a local, excellent place in Van Nuys. I was all coded out, which made for a perfect transition to the party at Andy Bandit's that night, conveniently just 6 miles from Kennys.

All in all, a fine Saturday.

No comments: