[SOLVED] How to add Materialized Views in rails 5

How to add Materialized Views in rails 5

I want to add a Materialized Views for avg rating.

My Rate model is:

class Rating < ApplicationRecord
  belongs_to :post
  validates_presence_of :rate
  validates_inclusion_of :rate,in: 1..5
end

My Post Model is:

class Post < ActiveRecord::Base
  has_many :ratings
  accepts_nested_attributes_for :ratings
end

I want to find Avg for the post Using Materialized view as

<%= "Avg.rate:#{post.ratings.average(:rate).to_f.round(2)}"%><br>

I created a migration for MV as

class CreateAvgMatView < ActiveRecord::Migration[5.1]
  def change
    execute <<-SQL
      CREATE MATERIALIZED VIEW rateavg_matview AS
      SELECT AVG("ratings"."rate") FROM "ratings"
    SQL
  end
end

I find a issue like

D013:post_app naren$ rake db:migrate
== 20180813080437 CreateAvgMatView: migrating =================================
-- execute("      CREATE MATERIALIZED VIEW rateavg_matview AS\n        SELECT AVG(\"ratings\".\"rate\") FROM \"ratings\"\n\n")
rake aborted!
StandardError: An error has occurred, this and all later migrations canceled:

SQLite3::SQLException: near "MATERIALIZED": syntax error:       CREATE MATERIALIZED VIEW rateavg_matview AS
        SELECT AVG("ratings"."rate") FROM "ratings"

Solution

SQLite does not support materialized views. Please read more here How can a materialized view be created in sqlite?

You'd have to switch to different RDMS (e.g. PostgreSQL) or create a "normal" table and use trigger to update it.