HasFields

HasFields provides you with a way to have multiple scoped dynamic key value, attribute stores persisted in the database for any given model. These are also known as the Entity-Attribute-Value model (EAV).

Installation

In your Gemfile:

gem "has_fields"

Do a bundle install, then for each model you want to have custom fields (say User with an organization scope for the fields and attributes) do the following:

$ rails generate has_fields:install User organization

Then check and run the generated migrations

$ rake db:migrate

Then add the has_fields class method to your model:

class User < ActiveRecord::Base
  has_fields :scopes => [:organization]
end

Normally has_fields stores information in three tables:

fields - the name and type of the info being stored, and the scope id attributes - the actual info, linked to the field and to the original class (User) select_options - if the field has a 'select' type, the select options can be stored here

If these table names appear to be too general or you want to use different tables for different calling classes, you can pass in a number of options (listed in the lib/has_fields/class_methods.rb file).

Description

What is Entity-attribute-value model?

Entity-attribute-value model (EAV) is a data model that is used in circumstances where the number of attributes (properties, parameters) that can be used to describe a thing (an "entity" or "object") is potentially very vast, but the number that will actually apply to a given entity is relatively modest.

Typical Problem

Say you have a contact management system, and each person in the database belongs to an organisation. That organization may have a bunch of values that need to be stored in the database, such as, primary contact name, or hot prospect?

Each of these could be stored as column values on the organization table, but you could have 10-20 of these, and adding a new one would require a database change.

HasFields allows you to define these key values simply with an attribute type.

Example

Following on from the installation section above, we have a User with the following fields setting:

class User < ActiveRecord::Base
  has_fields :scopes => [:organization]
end

We can now find the fields for the organization.

@organization = @user.organization
@organization_fields = User.field_fields(:organization, @organization.id)

This returns an array full of UserFields that will look something like:

UserField id: 104, name: "High Potential", style: "checkbox", select_options: nil

Which could then be rendered out into a HTML page like so (logic in HTML for demonstration purposes, would be better to do this as a helper method)

<% @organization_fields.each do |field| %>
  <p>
  <% case field.style %>
  <% when 'checkbox' %>
    <%= f.check_box field.name %>
  <% when 'text' %>
    <%= f.text_field field.name, @user.fields[:organization][@organization.id]['High Potential'] %>
  <% end %>
  </p>
<% end %>

Running the Specs

Ruby Environment

You should run the unit tests under ruby-1.9.2, a sample .rvmrc would be:

$ cat .rvmrc rvm ruby-1.9.2@has_fields --create

Once you have the right ruby, you should bundle install. Running the specs then is done with:

$ rake spec

Creating the test database

The test databases will be created from the info specified in spec/db/database.yml. Either change that file to match your database or change your database to match that file.

Copyright (c) 2008 Marcus Wyatt, released under the MIT license