Most of the time in a web application, a single API request consists of multiple database queries. For example: class DashboardsController < ApplicationController def dashboard @users = User.some_complex_scope.load_async @products = Product.some_complex_scope.load_async @library_files = LibraryFile.some_complex_scope.load_async end end Quoting snippet from load_async PR description from rails repository. The queries are executed synchronously, which mostly isn’t a huge concern. But, as the database grows larger in size, the response time of requests is getting longer. A significant part of the query time is often just I/O waits.

Sometimes dealing with DB processes in a Rails application consume a lot of time. Often there are a bunch of small and simple DB queries that go endless. For example, bulk insertions or bulk updates in tables. Dividing it into various background jobs is an idle solution. In a few scenarios, we can't prefer background jobs e.g. the change you apply, makes the existing data invalid. In this article, we will see how to complete a large set of DB queries under minutes which would otherwise take hours if not optimized. It's a better practice to create a rake

While performing concurrent operations, a database must ensure data integrity. ACID compliant relational database ensures this data integrity through its locking mechanism. ACID = Atomicity, Consistency, Isolation, Durability Locks can be at the database, table, page, or row level. Here is a beginner's guide to database locking in PostgreSQL. In this article, let's see how Rails provides a mechanism for optimistic locking on ActiveRecord models. However, before we proceed, let us first understand the basics of optimistic and pessimistic locking. What is optimistic locking? Let's take an example of two admin users, Mohan and Ritesh, managing the product inventory in their

Recently while working on one of our project there was an requirement of tracking count of records associated with has-many association. But also there was "is_hidden" flag set on some of the records which I do not suppose to count in counter as those were hidden records. So default counter_cache option of rails active-record was not appropriate in this case which automatically counts and caches the number of associated records and keeps cache updated. Refer following model code for this. class Order < ActiveRecord::Base belongs_to :customer, counter_cache: true end class Customer < ActiveRecord:

Performing an action via a callback is fairly easy and doable. Sometimes requirement may be a bit enhance that we need to track every change now and then. On the same note, if we have associations and we wanted to make some changes that needs to be reflected on previous and new values, this dirty concepts can save our time. This module gives a way to track changes done in an active-record object. By default, rails include ActiveRecord::Dirty this module. This gives many powerful methods that helps us to track attribute changes. This methods are based on the attribute

This is an awesome link on how to setup attributes on ActiveRecord LINK: 5-ways to set attributes And I want to mention one trick about active record: When we try to assign a value to active record object like class A In case of any queries, post your queries in comments.

ActiveRecord::Base#find_in_batches. This lets you iterate over all the records in cursor-like fashion (only retrieving a set number of records at a time into the memory): @Subscription.find_in_batches(batch_size => 100 ) { |subs| subs.each { |s| ... } }@ iterate over all subscriptions in chunks of 100 find_in_batches supports scopes @class Subscription < ActiveRecord::Base scope :expired, :conditions => { :expired => true } end @ @Subscription.expired.find_in_batches(:batch_size => 100 ) { |subs| ... }@ _Disadvantage: _ You can’t specify :order or :limit in the options. Where to use it: Large Dataset, where you need to loop through

What is Mass Assignment? Assigning multiple attributes of a record with params received from the application within a single query. For example,{:user => {:first_name => "FirstName", :last_name => "LastName", :role => "admin"}} So while creating a new record in User table, we specify as => User.create(params[:user]) In the above query, rails gives the freedom for one-to-one mapping of params attributes with model-record attributes. Lets say, we don't explicitly specify as User.create(:first_name => params[:user][:first_name], :last_name => params[:user][:last_name].......). Such assignments