Census is a Rails plugin that collects searchable demographics data for each of your application’s users. The data to be collected is defined using a simple admin interface that Census provides.

After installing the Census gem, require it in your Rails app and run the census generator.

In your config/environment.rb:

config.gem 'census'

Run the generator and migrate your database:

script/generate census
rake db:migrate

The generator creates a sample configuration file in config/initializers/census.rb. At the top of this file, you’ll see a configuration option that allows you to restrict access to the Census admin user interface. You’ll probably want to set this option, or anyone will be able to access the admin UI. Assuming your app has an authentication system that implements a current_user method, and that your user model has an admin? method, you could do something like this:

Census.configure do |config|
  config.admin_role = 'current_user.admin?'
end

The remainder of the configuration file defines various data types that you can use for the data you’ll be collecting. Census comes with a few data types already defined, and you can add additional types if needed. When defining a data type, you can provide various Ruby procs that are used to convert the data to and from a string representation that will be stored in the database. The procs you can provide are:

• :sql_transform - returns a SQL fragment that will be used for comparing data when doing search queries

• :format_data - used to convert data from its string representation

• :validate_data - used to validate form field submissions, and should return nil if the data is valid or an error message if it is invalid

As an example, here’s the data type definition for integer data:

Census::DataType.define(
  "Number",
  :sql_transform  => lambda {|column_name| "CAST(#{column_name} AS SIGNED INTEGER)"},
  :format_data    => lambda {|data| data.to_i unless data.blank? },
  :validate_data  => lambda {|data| "must be a number" unless data =~ /^\d*$/}
)

You can access the Census admin UI at /census/admin. You may want to add a link to census_admin_path somewhere in your app’s administration interface. Using the admin interface, you’ll be able to create questions and their optional multiple-choice answers. Questions are organized into data groups and can be reordered using drag and drop.

You could also create DataGroup, Question, and Choice instances programatically if you’d prefer not to use the admin UI.

Census provides a partial that you can include in a form that collects answers from your users. This partial assumes it’s inside of a form_for(:user) block. It will render fields for each of the questions you’ve defined.

<%= render 'census/user_questions', :user => @user %>

Data groups are rendered as fieldsets that contain a list of input fields, one for each question. If you take a look at the rendered HTML, you’ll see several class and id attributes that you can use to style the form fields as needed.

Census provides a partial that you can use to display a user’s answers. Somewhere in your app, probably in users/show.html.erb, add the following to render the partial:

<%= render 'census/user_answers', :user => @user %>

From your User object, you can get to that user’s answers using methods that are automatically generated for each of your data groups and questions. For example, let’s assume you have a data group called “Physical Attributes” with questions for “Weight” and “Hair Color.” You can retrieve a user’s answers like this:

user.census_data.physical_attributes.weight user.census_data.physical_attributes.hair_color

If your data group and question names change frequently, or if you’ve exposed the census admin UI so that the questions can be changed by your users, you’ll probably want to avoid relying on the auto-generated method names. Instead, you can access the user’s answers using strings, like this:

user.census_data['Physical Attributes']['Weight']
user.census_data['Physical Attributes']['Hair Color']

Starting with version 0.4.2, census allows you to expose its data as attributes directly on your model class. This is especially useful if you’re trying to display census answers in forms and you’d like Rails’ default form handling to work for that data.

If we assume that you have census questions defined as in the previous section, you can add the following in your User class:

expose_census_data('Physical Attributes', 'Weight', :weight)
expose_census_data('Physical Attributes', 'Hair Color', :hair_color)

And then you can get or set the census answers directly on the user, like this:

user.weight = 148          # set the user's weight
user.weight                # returns 148

user.hair_color = "Blond"  # set the user's hair color
user.hair_color            # returns "Blond"

Census provides a search interface for finding users whose answers match a list of search criteria. To perform a search, first create a Census::Search object, passing your search criteria as a hash of questions and values. We’ll assume for this example that we have questions for “Hair Color” and “Age,” and we’ll look them up by name.

hair_color = Question.find_by_prompt('Hair Color')
age = Question.find_by_prompt('Age')
search = Census::Search.new(hair_color => 'Brown', age => 25)

The search listed above will find all users who have brown hair and are 25 years old. You can also pass arrays or ranges, like this:

search = Census::Search.new(hair_color => ['Brown', 'Blond'], age => 25..30)

That search will find all users between the ages of 25 and 30 that have either brown or blond hair. Once you’ve created the Search object, call its perform method to query the database and get back the list of matching users.

users = search.perform

In order to run the test suite for Census, first make sure you have all of the dependencies installed. Then, you need create a blank rails app in the test/rails_root folder and add ‘shoulda’ and ‘factory_girl’ as gem dependencies for that app’s test environment (test/rails_root/config/environments/test.rb).

The default rake task runs the test suite for Census.

Copyright © 2010 Envy Labs LLC. See LICENSE for details.