RoR, Judge Judy, and little old ladies

[Andrei Alexandrescu (See Website For Email)]

Robby wrote:
> Andrei Alexandrescu (See Website For Email) wrote:
>> After yesterday's hubbub, Judge Judy called and punished me to read 
>> about RoR, in addition to the obligatory sentence of helping a little 
>> old lady cross the street five times a week.
>>
>> So I went and read the nice tutorial at:
>>
>> http://www.onlamp.com/pub/a/onlamp/2006/12/14/revisiting-ruby-on-rails-revisited.html 
>>
>>
>> I have a couple of questions that I assume will be easy to answer by 
>> anyone who actually has used RoR.
>>
>> On the second page of the tutorial, the authors describe how they 
>> write SQL code to create tables, and then how they invoke Ruby to 
>> parse that SQL code and generate (I assume) Ruby wrappers for it.
>>
>> Now consider that the database changes: new tables, new fields, 
>> different types for existing fields, etc.
>>
>> 1. Is now the generated Ruby code is out of sync with the database?
>>
>> 2. In case it is out of sync, what is the way to bring it back in 
>> sync? Manual editing of the Ruby code? Editing the SQL and then 
>> regenerating the wrappers? Some automated way?
>>
>> An additional question: most interesting work in databases is done 
>> through views (SELECT statements) and stored procedures. Can Ruby 
>> parse such stuff and generate appropriate wrappers? If so, what 
>> happens when the views and stored procedures change?
>>
>> I'm asking these questions because I want to figure whether automating 
>> the task of keeping in sync with a database, plus the additional type 
>> safety and speed, are significant advantages in the Web/DB domain. In 
>> such a scenario, error messages like the one in Part 2 
>> (http://www.onlamp.com/pub/a/onlamp/2007/01/05/revisiting-ruby-on-rails-revisited-2.html?page=4) 
>> may be avoided; the code simply fails to compile. I know of domains 
>> where such advantages are very important, but I'm not sure how the 
>> Web/DB domain feels about it.
>>
>>
>> Andrei
> 
> 1 & 2 depend on a couple of things in relation to RoR.
> 
> Since classes absorb the schema of the table they represent, if a data 
> type of a column changes, it can handle it in the means of generic find, 
> save, etc. However, if there is logic in the code that depends on that 
> type, it's obviously going to fail.

Makes sense. So if all Ruby does is e.g. display a column, which I 
assume is a generic operation with uniform syntax over all types, the 
type of that column could be anything. If, on the other hand, Ruby does 
some math against a column, and that column changes from number to 
string, runtime errors would ensue.

What if there is a web page that accepts that column? Say the old type 
was a string (so the appropriate form field is a textbox), and the new 
type is a date (so the appropriate form field is three drop-down boxes). 
Is Ruby's HTML generator going to figure things out and spit the 
appropriate HTML page?

> Again with the addition of a column, it's absorbed by the class (meaning 
> that there is a property generated at runtime for access to the class 
> implementation.

Alright. And are there any operations (e.g. "print all columns") that 
will naturally encompass the new column too?

> If a table is added RoR doesn't care about it, but you can't use it in 
> an association, due to the fact that the machinery needed for 
> represented associations needs to be generated against that new table.

Interesting. So here's a limitation that might be addressed. Do all of 
today's database engines (e.g. mysql) offer structure inspection (e.g. 
"enumerate tables in this database", "enumerate fields in this table"...)?

> So how does it handle changes? Pretty blindly, as long as your changes 
> don't change any logic you've predetermined into some code. including 
> associations (like belongs_to (where you've changed the name of the 
> foreign key)
> 
> Bonus Question:
> Rails is pretty ignorant of the relationships defined in the database 
> itself DHH (author of RoR) has his reasonings listed here
> http://www.loudthinking.com/arc/000516.html

Interesting. I happen to disagree with the author, and the "you'll have 
to pry that logic from my dead, cold object-oriented hands" part 
definitely sets off a blinking red LED somewhere, but I'm not a DB 
expert nor a Ruby expert so possibly I'm even misunderstanding things.

I'm not even thinking of stored procedures as logic vehicles. All stored 
procedures I've dealt with were little more than simply stored views 
(SELECT statements). If I want to see customer phone numbers and their 
orders, I'm glad to let the database do that efficiently by doing an 
inner join and passing me the information in one shot, instead of having 
me look at the two relevant tables for the sake of object orientedness. 
To say nothing about data integrity, which is best taken care of at the 
database level.

The whole idea of manipulating data at table level and compulsively 
delaying absolutely all meaning to the application level reminds me of 
dBase and the 1980s.

Anyhow, what I think might be good for most people is to write a SELECT 
statement that does something, and have the columns of that SELECT 
automatically available for further processing. I understand RoR doesn't 
do that.

> I have read about hacks to get procs to work under oracle, though I 
> really haven't invested any time to the situation, as I've never used 
> the db (firebird mainly)
> 
> (Not Defending his choices, nor am I an authoritative voice on RoR, 
> besides the couple of patches back to it, I'm just a user - though 
> limited as of late).
> 
> If these answers don't answer what you're looking for feel free to let 
> me know

Thanks, the answers were exactly to the point. By and large, I'm 
interested in seeing strengths and limitations in the RoR approach, and 
making an impression whether a more static approach would make a big 
difference (better DB <-> code binding, better error detection, faster 
execution).

After all, the approach wouldn't even feel much more static: with rdmd, 
fast compilation, and the bang syntax, D can pretty much have the feel 
of an interpreter.


Andrei