Skip to main content

Experiences Using "Build Your Own Ruby On Rails Web Applications"

This is the first of a series of tech posts on this blog. I'm studying RubyOnRails, (RoR), using an excellent book: Build Your Own Ruby On Rails Web Applications . The book is easy to understand and flows well in a narrative fashion with plenty of humor thrown in. As I build my real-world application I'll post notes of interest here. These posts are intended for RubyOnRails beginners or others reading the book.

Model class to database table naming:
I understood from the book that a model class like 'Story' would be translated into a table name in a migration file of 'story'. What I was not aware of was that a name like 'MyBigStory' will be translated into a table name of 'my_big_story'.

rake and rolling back database migrations:
First, this feature of RoR is incredible! Essentially it's revision control for database schemas! With a minimum of work, the developer can maintain a framework that allows her to easily move back and forth between versions of the schema. The generated migration files go a long ways towards making this feature convenient to use.

There is a typo in the book around rolling back versions. The command in the book is:

rake db:migrate -VERSION=n

the command should read:

rake db:migrate VERSION=n

Most importantly, this typo led me to re-read the beginning of the book where it is noted that all errata will be published at the books online errata page.

Of course, the question arises, why did I need to do a rollback of a schema so soon? I typed in an incorrect column name for a table column. So, on page 187 of the book where the author adds a story_id column, I added a stary_id column. Because of the errata, I was unable to roll back the migration. It didn't seem right to roll back the migration and lose the development history anyway. So, I moved forward and created a new migration to correct the misnaming.

First, ruby was used to create a new migration file:

rruby script/generate migration RenameID

The new migration simply used the following rename_column method in the migration file's self.up method:

rename_column :votes, :stary_id, :story_id

In the self.down method, the change was reversed with:


rename_column :votes, :story_id, :stary_id

I then ran

rake db:migrate

rake pulled in the new migration file, changed the column name and all was well!


Comments

CresceNet said…
Hello. This post is likeable, and your blog is very interesting, congratulations :-). I will add in my blogroll =). If possible gives a last there on my site, it is about the CresceNet, I hope you enjoy. The address is http://www.provedorcrescenet.com . A hug.

Popular posts from this blog

Cool Math Tricks: Deriving the Divergence, (Del or Nabla) into New (Cylindrical) Coordinate Systems

The following is a pretty lengthy procedure, but converting the divergence, (nabla, del) operator between coordinate systems comes up pretty often. While there are tables for converting between common coordinate systems, there seem to be fewer explanations of the procedure for deriving the conversion, so here goes!

What do we actually want?

To convert the Cartesian nabla



to the nabla for another coordinate system, say… cylindrical coordinates.



What we’ll need:

1. The Cartesian Nabla:



2. A set of equations relating the Cartesian coordinates to cylindrical coordinates:



3. A set of equations relating the Cartesian basis vectors to the basis vectors of the new coordinate system:



How to do it:

Use the chain rule for differentiation to convert the derivatives with respect to the Cartesian variables to derivatives with respect to the cylindrical variables.

The chain rule can be used to convert a differential operator in terms of one variable into a series of differential operators in terms of othe…

Lost Phone

We were incredibly lucky to have both been in university settings when our kids were born.  When No. 1 arrived, we were both still grad students.  Not long after No. 2 arrived, (about 10 days to be exact), mom-person defended her dissertation and gained the appellation prependage Dr. 

While there are lots of perks attendant to grad school, not the least of them phenomenal health insurance, that’s not the one that’s come to mind for me just now.  The one I’m most grateful for at the moment with respect to our kids was the opportunities for sheer independence.  Most days, we’d meet for lunch on the quad of whatever university we were hanging out at at the time, (physics research requires a bit of travel), to eat lunch.  During those lunches, the kids could crawl, toddle, or jog off into the distance.  There were no roads, and therefore no cars.  And, I realize now with a certain wistful bliss I had no knowledge of at the time, there were also very few people at hand that new what a baby…

Lab Book 2014_07_10 More NaI Characterization

Summary: Much more plunking around with the NaI detector and sources today.  A Pb shield was built to eliminate cosmic ray muons as well as potassium 40 radiation from the concreted building.  The spectra are much cleaner, but still don't have the count rates or distinctive peaks that are expected.
New to the experiment?  Scroll to the bottom to see background and get caught up.
Lab Book Threshold for the QVT is currently set at -1.49 volts.  Remember to divide this by 100 to get the actual threshold voltage. A new spectrum recording the lines of all three sources, Cs 137, Co 60, and Sr 90, was started at approximately 10:55. Took data for about an hour.
Started the Cs 137 only spectrum at about 11:55 AM

Here’s the no-source background from yesterday
In comparison, here’s the 3 source spectrum from this morning.

The three source spectrum shows peak structure not exhibited by the background alone. I forgot to take scope pictures of the Cs137 run. I do however, have the printout, and…