Book Review, “Pro Active Record”
Published by Apress
By Kevin Marshall, Chad Pytel, Jon Yurek
Book Info
Sample Chapter: Ch. 01 - Introducing Active Record
Table of Contents
Years ago when I was in PHP Land (now I travel quite a bit more! haha), I strugged for months with how to write a good ORM . It was tough, because I wanted to abstract the "boring logic" of retrieving records from a database without writing SQL but still remain flexible enough. I never really came up with a good model. I used the DAO from "extreme php" library which I think was a knock off from java. It was ok, but I still didn't feel like I had "arrived".
When I discovered Ruby on Rails, I found ActiveRecord. Ahh HA! Finally, this is what I was looking for. At first I thought it was part of Rails, but its not. Its a standalone library and you can use it with straight up ruby scripts.
I got a review copy of "Pro Active Record" some time ago and read it some when I got it, then some later, and now I am going to officially write up a review!
If you do anything with Active Record, get this book. The things that are briefly mentioned in most Rails books are described in detail in this book.
Chapter 1 - Introducing Active Record
Most of the time, the first chapters of a book are boring to me. I don't need another "History of the Internet" or how "HTML was developed" ... blah blah. But this one, the story is only 1 page. And it actually has some introductory scripts on using Active Record, so you can see right away how it works. It also explains the benefits of MVC and why ORMs are good. Some people still don't get it!
Chapter 2 - Active Record and SQL
This chapter helps you translate the "sql in your head" to how to write it with Active Record. I've used Active Record so much that now I have forgotten most of my SQL, which is kind of embarrassing. 
I now find writing sql tedious and boring! I would have actually called this chapter "Demystifying Active Record" since it explains why all the dynamic finders work. You'll also find transactions and locking explained here.
Chapter 3 - Setting up Your Database
Migrations! The Awesome Thing that can turn into a nightmare for large rails projects with multiple developers.... definitely have to decide on some best practices with your team on this one. The chapter has only one thing to say about this -- assume any checked in migration has already been run by your team and the migration should not be edited and checked back in! You'll have to make another migration file with your changes.
[tip]
Nola's Note: When you make a migration, test it both UP and DOWN!! Here's what I do --
write a migratiion
rake db:migrate (go up to the version with new code)
rake db:migrate VERSION=n-1, (go to version before the latest)
rake db:migrate (back to lastest)
rake db:migrate VERSION=0 (back to blank db)
rake db:migrate (back to latest)
[/tip]
Just to be sure its all good -- even on a new database!
Chapter 4 - Core Features of Active Record
Now is the fun stuff - Callbacks. This is magic. This makes Active Record so flexible, and is one thing I could never figure out how to do with my PHP ORMs. I use call backs to set defaults for fields. If its just a straight default, then I set it in the database but if I need to make a decision, (if this field then this field..) then I can use it in a callback.
Associations - at first this is very confusing! I don't know how many times I got "has_many" and "belongs_to" mixed around in the beginning.
Validations - Awesome. I had to do some ruby code without a database and I really really really missed the validations. It took me like 5x longer than it should! Understanding all of these validation methods will make your life so much more enjoyable. I really really hate doing boring, repetitive stuff...it seems so wasteful to me.
Chapter 5 - Bonus Features
Everybody likes a bonus and this isn't even the last chapter of the book.
Java people will like the Active Record Observers -- seems a little AOP to me (aspect orienteted programming) and something I probably have neglected to use to their fullest extent.
Acting up -- Learn how to "save time" with the "acts_as" magic: List, Tree, Nested Sets. If your data needs these structures, you got it made. I can imaging how much longer it would take to write this stuff in perl or php.
Composed of - I haven't used this, but this looks like a good way to make sensible objects out of database tables. There is quite a bit of explanation and examples of this, it will come in handy.
There are a few other in depth explanations of things, such as method_missing which is how alot of the magic happens. Rock on.
Chapter 6 - Active Record Testing and Debugging
Ahh yes, Testing. My favorite subject. My friends who know how much I love testing say I am sick. I must have an inner need to PROVE I am right or something, haha.
The chapter goes into depth about using test_unit with Active Record, sadly no RSpec. But, it does go into all the error messages that Active Record throws so you can write good try/catch blocks and make very exact error messages (probably best logged for the admin rather then displayed to the user!)
Chapter 7 - Working with Legacy Schema
Here's how you work with that old database that just won't die... or that management won't let you totally redo. Active Record follows some of the principles of Rails "convention over configuration" ... relying on table and column naming conventions to figure out how to build your object....but still giving you a way out if you want your tables singular and your primary id field called "myawesomeid" instead of "id"
I've used some of these things on an older database and it was possible! Not too bad if thats what you have to work with.
[soapbox]
Some people find this annoying "oh gosh! my library can't make decisions for me! OMG! That sucks" .. to that I say, "Umm ok. But if you follow these conventions then I can come into your project and know exactly what is going on" ... like with web standards, we all harp on how IE and FF do things differently, yet people want to bellyache about Active Record preferring to have plural names and id field called "id". Right.
Follow the dang convention and find something worth complaining about to complain about.
[/soapbox]
Chapter 8 - Active Record and The Real World
This chapter goes into depth about the library and encourages you to go read the Active Record code. Always a good idea to know what it is you are using I've actually learned ruby better by reading source code. The chapter walks you through basic structure of the files. Very cool.
[soapbox]
I used to work at a place that didn't like any "outside code" because they were afraid "OMG ... it will send our passwords to Russia!" ... ok, well I am not an idiot. I read over any code that I use that I didn't write. I look at the tests to see if I am using it right. I even RUN the tests so I can be sure its working as advertised.
[/soapbox]
Alternatives to Active Record - with EXAMPLES! If something about Active Record doesn't set too well with you, take a look at the alternatives. Sometimes I look at the alternatives and decide that the first wasn't so bad after all. You'll find examples of DBI, Og, ActiveRelation.
Finally a section on Q and A finishes up this book. The Appendix has a complete reference of ActiveRecord methods to make this book a well rounded reference, tips, documentation and very handy to have at your desk!