Connecting to Remote DB with psql

psql -h host.crap.com -U user_name -d database_name

For more options, see the postgres manual: http://www.postgresql.org/docs/8.1/interactive/app-psql.html

Example of Using svn:externals

svn propset svn:externals "ucb_tasks $svn_commons/ucb-rails-application-scaffold/trunk/lib/tasks" ucb_rails_logs/lib/tasks

Ruby / Rails and Web Services

Making web services in Rails is pretty easy. Recently I created a test web service following the instructions located here: http://manuals.rubyonrails.com/read/chapter/67

For this example, I'm going to create two web services. One will interface with a Color API and the other with a Person API. For the Color API, we need to create a color model, extending ActiveRecord::Base. The color model should have 1 attribute (db column): "name". Now create a person model, extending ActiveRecord::Base, and give it the following attributes: first_name, last_name, email. As always, these classes go in the models dir of your Rails app.


Here are the migrations for populating your tables:

class AddColorsTable < ActiveRecord::Migration
  def self.up
    create_table :colors do |t|
      t.column :name, :string
    end
  end

  def self.down
    drop_table :colors
  end
end

class AddPersonTable < ActiveRecord::Migration
  def self.up
    create_table :people do |t|
      t.column :uid, :string
      t.column :first_name, :string
      t.column :last_name, :string
      t.column :email, :string
    end
  end

  def self.down
    drop_table :people
  end
end

Next, use script/generate to fire off the creation of the web service:

rooster> script/generate web_service remote


This creates an "apis" directory beneath the "app" directory and adds one file to it: "remote_api.rb." It also adds a "remote_controller.rb" to the controller directory. We're going to use delegated dispatching so we don't need the remote_api.rb class, deleted it, I did :-). If you care, you can read all about the different dispatching types at the above URL.

Now add the following to your remote_controller.rb file:

class RemoteController < ApplicationController
  web_service_dispatching_mode :delegated
  web_service_scaffold :invoke
  
  web_service :person, PersonService.new
  web_service :color, ColorsService.new
end

Brief explanation of the class:
web_service_dispatching_mode: specifies dispatch type
web_service_scaffold: this allows us to test our web server by going to: localhost:3000/remote/invoke
web_service: name, instantiate (this declares one of our web services).


Ok, let's create the PersonService. Add the below classes to the "apis" directory.

person_service.rb:
class PersonService < ActionWebService::Base
  web_service_api PersonApi
 
  def find_all
    Person.find(:all)
  end

  def find_by_name(last_name, first_name)
    hash = {:first_name => first_name, :last_name => last_name}
    hash.reject! {|key, val| val.blank?}
    query_string = hash.map {|key, val| "#{key} = '#{val}'"}.join(" and ")
    
    return [] if query_string.blank?
    Person.find(:all, :conditions => query_string)
  end
end

person_api.rb
class PersonApi < ActionWebService::API::Base
  api_method :find_all,
             :returns => [[Person]]
            
  api_method :find_by_name,
             :expects => [{:last_name => :string}, {:first_name => :string}],
             :returns => [[Person]]
end

Now the ColorsService:

colors_service.rb
class ColorsService < ActionWebService::Base
  web_service_api ColorsApi
 
  def find_all_colors
    Color.find(:all).map {|c| c.name}
  end

  def find_color_by_name(name)
    c = Color.find_by_name(name)
    c.name unless c.nil?
  end
end

colors_api.rb
class ColorsApi < ActionWebService::API::Base
 
  api_method :find_all_colors,
             :returns => [[:string]]
 
  api_method :find_color_by_name,
             :expects => [{:color_name => :string}],
             :returns => [:string]
end

You can view the WSDL for these services by going to: http://localhost:3000/remote/service.wsdl. Note, the wsdl contains info for both services.


Ok, so now let's test our service. Fire up irb so we can play a nice game of Simon Says.

rooster@banway28 > irb
irb(main):001:0> require 'soap/wsdlDriver'
=> true

irb(main):002:0> driver = SOAP::WSDLDriverFactory.new("http://localhost:3000/remote/service.wsdl")

=> #
irb(main):003:0> person_rpc = driver.create_rpc_driver("Service", "PersonPort")

=> #>
irb(main):005:0> color_rpc = driver.create_rpc_driver("Service", "ColorPort")

=> #>
irb(main):006:0> color_rpc.findAllColors

=> ["red", "green", "blue", "yellow", "orange", "black", "white"]
irb(main):007:0> person_rpc.findAll
=> [#, #, #, #]

irb(main):008:0> person_rpc.findByName("", "steven")
=> []

irb(main):009:0> person_rpc.findByName("", "steve")
=> [#, #]

irb(main):010:0> person_rpc.findByName("", "steve").first.first_name
=> "Steve"

Pretty neat stuff eh? The key thing to keep in mind, is that with delegated dispatching, you need to create separate rpc drivers for each API you want to interact with. That's why I created the person_rpc and colors_rpc objects.


Next time I'll show you how to update/create data using SOAP and ruby.

Installing Rubygems in a Non-Standard Dir

From the rubygems FAQ: http://rubygems.org/read/chapter/15

You have to redefine the location of the GEM_HOME variable and add the paths to the gem repositories in the RUBYLIB variable before launching the installation into a custom directory.

GEM_HOME should point to $PREFIX/lib/ruby/gems/1.8 if it used with the 1.8 version of ruby.

RUBYLIB should point to the $PREFIX/lib/ruby and $PREFIX/lib/site_ruby/1.8

Here is a shell script that runs in the rubygems distribution directory to install into /home/user :

PREFIX=$HOME
export GEM_HOME=$PREFIX/lib/ruby/gems/1.8
export RUBYLIB=$PREFIX/lib/ruby:$PREFIX/lib/site_ruby/1.8
ruby setup.rb all --prefix=$PREFIX

You may add GEM_HOME and RUBYLIB into your ~/.profile file to automatically load on login.

Uninstalling MySql on OSX

Recently I installed mysql-5 on my laptop using the .dmg installer. Later I decided that I wanted to use mysql-4 instead. Since there is no mysql uninstaller for os x, I did [rm -rf /usr/local/mysql], thinking this would do the trick. The problem, however, is now when I try to install mysql I keep getting the message "You cannot continue. There is nothing to install." After poking around a bit more I found out that you need to delete the "mysql*.pkg/" directories located in /Library/Receipts

That did the trick!

Finally Got Mysql/Postgres Gem to Install

The incantation:

gem install mysql -- --with-mysql-lib=/opt/csw/lib/mysql --with-mysql-include=/opt/csw/mysql5/include/mysql

gem install postgres -- --with-pgsql-lib=/opt/csw/postgresql/lib --with-pgsql-include=/opt/csw/postgresql/include

The reason this was tricky, is because our sysadmin guys didn't install the mysql-devel libraries. They did however install the mysql4rt (runtime) stuff. I ended up installing the devel libraries in my home directory while the sysadmin guys get around to it.

Somewhat related, is how I improperly used ruby's [mkmf] library to debug the gem installation. Each gem that needs to build C extensions, uses an extconf.rb file that runs a bunch of crap and ends up generating a Makefile. The extconf.rb file makes heavy use of ruby's [mkmf] library. Anyway, I noticed that the extconf.rb script kept bombing out during its call to: [find_library('mysqlclient', 'mysql_query', lib] where [lib = /path/to/static/lib/mysql]. This seemed odd since the [lib] var was pointing to the mysql static libraries that I installed in my home directory. So I tried using irb to isolate the problem:

irb(main):001:0> require 'mkmf'
=> true
irb(main):002:0> lib = "/path/to/static/lib/mysql"
=> "/path/to/static/lib/mysql"
irb(main):003:0> find_library('mysqlclient', 'mysql_query', lib)
=> false

WTF?

For some reason I thought that the find_library() function wanted to know the path to the static library 'libmysqlclient.a'. This is not the case, it actually wants the path to the location of the shared library 'libmysqlclient.so'. Once I figured this out, I was able build the extension and find_library() was able to find the library:

irb(main):001:0> require 'mkmf'
=> true
irb(main):006:0> lib = '/path/to/shared/lib/mysql
=> "/path/to/shared/lib/mysql"
irb(main):007:0> find_library('mysqlclient', 'mysql_query', lib)
checking for mysql_query() in -lmysqlclient... yes
=> true

The True Meaning of libx.a Files

I don't really know C very well, so I was surpirsed (and delighted) when I finally learned what all those libx.a files are. For example, if you have mysql installed on your system, go take a look in the mysql/lib directory. You should see a bunch of files ending in .a . These are archive files containing compiled C code, basically they are the same thing as a java .jar file. Who knew?

If you want to check the contents of the arhive you can use the [nm] command. Like [nm libmysqlclient.a]

Want to know if the arhive has a specific function? [nm libmysqlclient.a | grep mysql_query]