STI and has_many relationship with type column as key
I am using Single Table Inheritance to manage various types of projects. I decided to keep some information related to each type of project. So I created a new table "project_types" with the "model_type" field as the primary key. The primary key values are the values of the "table" field of the projects. Problem . When I try to bind the ObjectTypes object object, it always returns null.
>> p = Project.find(:first)
=> #<SiteDesign id: 1, type: "SiteDesign", name: "1", description: "dddd", concept: "d", client_id: 40, created_at: "2009-10-15 08:17:45", updated_at: "2009-10-15 08:17:45">
>> p.project_type
=> nil
Getting the projects associated with the ProjectTypes is fine. Is there a way to do this right?
Models:
class Project < ActiveRecord::Base
belongs_to :project_type, :class_name => "ProjectTypes", :foreign_key => "model_name"
end
class SiteDesign < Project
end
class TechDesign < Project
end
class ProjectTypes < ActiveRecord::Base
self.primary_key = "model_name"
has_many :projects, :class_name => "Project", :foreign_key => "type"
end
Migrations:
class CreateProjectTypes < ActiveRecord::Migration
def self.up
create_table :project_types, :id => false do |t|
t.string :model_name , :null => false
t.string :name, :null => false
t.text :description
t.timestamps
end
add_index :project_types, :model_name, :unique => true
#all project types that are used.
models_names = {"SiteDesign" => "Site design",
"TechDesign" => "Tech design"}
#key for model_name and value for name
models_names.each do |key,value|
p = ProjectTypes.new();
p.model_name = key
p.name = value
p.save
end
end
def self.down
drop_table :project_types
end
end
class CreateProjects < ActiveRecord::Migration
def self.up
create_table :projects do |t|
t.string :type
t.string :name
t.text :description
t.text :concept
t.integer :client_id
t.timestamps
end
end
def self.down
drop_table :projects
end
end
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No wonder you're in trouble. Going from a pure STI system to your current system, you are horribly breaking the patterns you use by mixing parts of one with parts of the other.
I would personally go for something like:
class Project < ActiveRecord::Base
attr_readonly(:project_type)
belongs_to :project_type
before_create :set_project_type
def set_project_type()
project_type = ProjectType.find_by_model_name(this.class)
end
end
class SiteProject < Project
end
class TechProject < Project
end
class ProjectType < ActiveRecord::Base
has_many :projects
end
with migrations:
class CreateProjectTypes < ActiveRecord::Migration
def self.up
create_table :project_types do |t|
t.string :model_name , :null => false
t.string :name, :null => false
t.text :description
t.timestamps
end
add_index :project_types, :model_name, :unique => true
#all project types that are used.
models_names = {"SiteDesign" => "Site design",
"TechDesign" => "Tech design"}
#key for model_name and value for name
models_names.each do |key,value|
p = ProjectTypes.new();
p.model_name = key
p.name = value
p.save
end
end
def self.down
drop_table :project_types
end
end
class CreateProjects < ActiveRecord::Migration
def self.up
create_table :projects do |t|
t.string :type
t.references :project_type, :null => false
t.text :description
t.text :concept
t.integer :client_id
t.timestamps
end
end
def self.down
drop_table :projects
end
end
It just clears things up and also helps clarify what you are doing. Your "ProjectType" table is purely for additional data, your inheritance tree still exists. I also threw some checks to make sure your project type is always set (and correct, based on the model name), and only stops you from changing the project type after you save it if the attribute is read-only.
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