Posting to REST APIs from mysql triggers

This was a fun crazy idea that turned out not to be so good in practice. If you have a mysql table you are monitoring for changes, you can use a trigger to do so (as long as you have a semi-modern version of msyql).

Sometimes you might want to notify another service of any change (remote logging service, message queue, etc). For instance, at 8z, when the price of a listing changes, this is an interesting event that other software should be notified of.

The first step is to install the mysql http UDF (all commands below are for centos).

$ sudo yum install curl-devel

$ CPPFLAGS="-I/usr/include/mysql"  ./configure --with-mysql=/etc/my.cnf   --enable-shared

$ make

This gives us a .la file (built with libtool) but luckily there’s a .so file hiding:

sudo cp .libs/mysql-udf-http.so.0.0.0 /usr/lib64/mysql/plugin/mysql-udf-http.so

Then, your remote rest service will probably want JSON, so you’ll want to visit the mysql udf hub. There lives a JSON function. I just grabbed the C file from github and compiled it: gcc -fPIC -shared -o lib_mysqludf_json.so -I/usr/include/mysql/  lib_mysqludf_json.c

After these are compiled you have to copy the .so files to the appropriate directory and then add functions as a privileged user, per usual UDF convention.

Now you can create a trigger that calls these functions.

delimiter $$
CREATE TRIGGER upd_check BEFORE UPDATE ON account 
FOR EACH ROW 
  BEGIN 
    IF NEW.amount > 0 THEN 
      set @json = select json_object(account_id,amount) 
      select http_post('http://restservice.example.com/account/post',@json); 
    END IF; 
  END;$$ 

delimiter;

Note that I didn’t actually implement this, so the code up above is based on my memory. If you try this and have some corrections, please leave them in the comments and I’ll update this post.

Why didn’t I actually implement this, after doing the better part of a day’s worth of research? The database is not the best place for this kind of logic. Error handling for triggers is weak–if the trigger failed for any reason (like the remote service was down), you would need to build an error logging system, or send an email. Also, if there are a number of updated rows, which all trigger outbound http calls, you might run into performance issues which would be difficult to replicate or analyze, and, most importantly, might impact your database’s ability to act as a database. The three tier architecture exists for a reason.

But, it was fun to investigate, and, as my colleague said, would have been cool if it had worked. If you are still interested, there’s more on this topic here.


Running a brown bag lunch series in your office

Courtesy of smoothfluid

Courtesy of maxually

Brown bag lunches are great opportunities for employees to share their knowledge, learn new skills, and bring a small company together.  By ‘brown bag lunch’, I mean an internal presentation lasting about an hour, made by an employee on an interesting topic of their choice.  The name comes from everyone bringing their lunch to work on that day, rather than eating out.

8z has been doing them for over two years, and here are some lessons.

  • Schedule them monthly, and one mont at a time.  Don’t try to schedule out the whole year.
  • Have presenters spend as little time as possible building a powerpoint.  It’s hard to get away from them as a structural crutch, but they don’t really add a lot of value.
  • Bring in real business situations.  One of the most memorable presentations occurred when presenters analyzed a recorded call during the presenation.
  • Have someone be point and recruit people individually.  Don’t count on volunteers, especially at the beginning.
  • It’s OK to miss a month or two if other stuff is going on.  Hello December.
  • Record them if you can.  All you need is an ipad and a youtube account.
  • Technical presentations (like application architecture) are appreciated by the business folks.
  • Everyone has something to say.
  • You can have people repeat every six months or so.
  • Some people won’t want to speak.
  • Presenting in pairs can work.
  • Make sure the presenter leaves plenty of time for Q&A.  8z budgets an hour for the talk and Q&A.
  • Schedule it so founders/executives attend.  This makes a powerful statement and exposes them to direct ideas.
  • Be prepared to capture changes/feedback from the presentation.
  • The departmental cross pollination is a major benefit.
  • Consider themed potlucks (mexican, breakfast for lunch, etc) instead of brown bag lunches.

How do you spread knowledge within your small company?


Building an automated postcard mailing system with Lob and Zapier

Courtesy of smoothfluid

Courtesy of smoothfluid

I was looking at automated paper mailing systems recently (and listed what I found), and was especially impressed with Lob, especially the ease of its API.

Among other printing services, Lob will let you mail a postcard with a custom PDF on both sides, or a custom PDF on one side and a text message on the other, anywhere in the USA for $0.94.  (Sorry, not sure about international postcards) The company for which I work sends out tens of thousands of postcards every quarter. The vendor which we use charges them a similar fee (less, but in the same ballpark) but there’s a manual process to deliver the collateral and no API. So an on-demand, one by one post card sending system is very interesting to me.

Note that I haven’t received the Lob postcard which I sent myself, so I can’t speak to quality. Yet.

The Lob API is a bit weird, because the request is form encoded rather than a JSON payload.  It also uses basic auth, but only the username, not the password. But the API seems to have all the pieces you’d need to generate all kinds of postcards–reminder postcards, direct mail postcards, photo postcards, etc.

After testing out the service via the web interface and cURL examples, I thought that it’d be fun to build a Zapier zap. In particular, being able to send a postcard for an entry in a Google spreadsheet seemed like a useful use case. Plus, Zapier is awesome, and I’d wanted to test out their integration environment for myself.

So, I built a Zapier integration for Lob, using the Zapier developer docs in combination with the Lob developer docs. It was actually easy. The most complicated step was translating the Zapier action data, which is a one or two dimensional array of typed data, into the Lob data format, which wanted a couple of text fields and two address arrays. Zapier has a scripting environment that let me modify data from APIs pre and post send, and even had an example about form encoded APIs. Zapier’s JavaScript scripting development environment was full featured, including syntax and error highlighting. It had no real debugging available, but I could use the venerable debug-by-log-statement method fairly easily.

Where could I take this next? Everywhere people use postcards in real life. The postcards depend on PDF files (see a sample), so if you are generating a custom postcard for each interaction things become more complex, but there are a few APIs (based on a 30 second google search, here and here) available for dynamic PDF generation. There are also limits on API call throughput, if I stuck to the Zapier integration–I could send at most 300 postcards a day, unless I managed multiple spreadsheets.

I see reminders of high value events (dentist, house maintenance, etc), contests and marketing as key opportunities for this type of service. And if I had a product where direct mail was a key component, using Lob directly would be worth serious consideration.

Regarding the Zap, I believe I cannot make this Zap available to anyone else. Since I’m not a representative of Lob, I couldn’t commit to maintaining this Zap, and Zapier doesn’t want to have any of their customers depending on an integration that could disappear or be unsupported at any time–a fair position.

If the Zapier or Lob folks want to take this integration and run with it, I’d be happy to share my code–just leave a comment. If anyone else is interested in being able to generate Lob postcards from a Google spreadsheet (or any other compatible API) via Zapier integration, let me know and I’ll see what I can do.


Google Spreadsheet Custom Functions With Spreadsheet Based Configuration

The business for which I work, 8z Real Estate, runs on Google spreadsheets–they are everywhere, and are especially powerful when combined with Google Forms. (Except in the tech department–we use more specialized tools like wikis and bug trackers.)

Recently I was cleaning up one of these spreadsheets and making it more efficient. This spreadsheet was an ongoing list of items that should be charged to various real estate agents. There was a fairly clear set of rules (person A should be charged this for item B, but not for item C, and person D should not be charged for items E, but should for item F). The rules were also fairly constant–not a lot of change. While they were clear, there were some intricacies that had tripped up some folks. And since there was real money involved, there was often a lot of time expended to make sure the charges were correct.

For all these reasons, it made sense to automate the charge calculations. Given the data was already in a Google spreadsheet, I decided a custom function was the best way to do this. The custom function could read from a configuration tab in the same spreadsheet with a list of people and items which would represent the charge rules. In this way, if there was a new item, a new row could be added to the configuration spreadsheet without requiring any help from a developer.

I was able to write the functions fairly quickly, using QUnit for Google Apps Script. I can’t recommend using QUnit highly enough–developing in Google Apps Script combines the joys of javascript (with its … intrinsic difficulties) and a remote execution environment that can be tough to debug. So, unit test your Apps Script code!

The initial implementation pulled data from the configuration tab with each custom function call. This naive implementation worked fine up to a couple of hundred rows. However, eventually this caused Exceeded maximum execution time errors. I believe this is because when the spreadsheet was calculating all the charge values, it was accessing the configuration spreadsheet range hundreds of times a second.

My next step was to try to cache the configuration data. I used stringified JSON stored in the cache service. Unfortunately, this caused a different issue: Service invoked too many times in a short time: cacheService rateMax. Try Utilities.sleep(1000) between calls.

Third time is the charm: have the function return multiple values. The configuration data is only read once, as is the list of items and names. These are iterated and the charges for all of them are calculated and returned in a double array to fill entire columns. Using this technique avoided the above issues, but created another one. Adding new rows with new items wouldn’t update the charges columns. Apparently there is additional, ill documented caching of custom function values. Luckily StackOverflow had an explanation: spreadsheets “evaluate your [custom] functions only when a parameter changes.” The way I worked around this was to pass a parameter to the custom function of the number of non blank rows of the spreadsheet: =calculateCosts(counta(A:A)). When a new row is added, the custom function is re-evaluated.

In the end I have written unit tested code that works in the way the business wants to work (in Google Spreadsheets), that runs on someone else’s infrastructure (Google’s), that can be configured by non technical employees and that will increase the accuracy of the charge calculations. Wahoo!



© Moore Consulting, 2003-2017 +