Added basic rate model and it's database schema

app/models/rate.rb

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+class Rate < ActiveRecord::Base
+end

db/migrate/001_create_rates.rb

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+class CreateRates < ActiveRecord::Migration
+  def self.up
+    create_table :rates do |t|
+      t.column :amount, :decimal, :precision => 15, :scale => 2
+      t.column :user_id, :integer
+      t.column :project_id, :integer
+      t.column :date_in_effect, :date
+    end
+  end
+
+  def self.down
+    drop_table :rates
+  end
+end

db/migrate/002_add_indexes_to_rates.rb

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+class AddIndexesToRates < ActiveRecord::Migration
+  def self.up
+    add_index :rates, :user_id
+    add_index :rates, :project_id
+    add_index :rates, :date_in_effect
+  end
+
+  def self.down
+    remove_index :rates, :user_id
+    remove_index :rates, :project_id
+    remove_index :rates, :date_in_effect
+  end
+end

spec/models/rate_spec.rb

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+require File.dirname(__FILE__) + '/../spec_helper'
+