Rails 5 ActiveRecord Queries Cheat Sheet

Active Record Queries

Find:	clients = Client.find([1, 10])	SELECT * FROM clients WHERE (clients.id IN (1,10))
Find By:	Client.find_by! first_name: 'Nobody'	SELECT * FROM clients WHERE (clients.first_name = 'Nobody) LIMIT 1	find_by! will raise an error if no record is found. # => ActiveRecord::RecordNotFound
Passing Params	Client.where("orders_count = ? AND locked = ?", params[:orders], params[:locked])
Passing Params as Hash	Client.where("created_at >= :start_date AND created_at <= :end_date", {start_date: params[:start_date], end_date: params[:end_date]})}
Between	Client.where(created_at: (Time.now.midnight - 1.day)..Time.now.midnight)	SELECT FROM clients WHERE(clients.created_at BETWEEN '2008-12-21 00:00:00' AND '2008-12-22 00:00:00')
Subsets: Find using SQL IN	Client.where(orders_count: [1,3,5])	SELECT * FROM clients WHERE (clients.orders_count IN (1,3,5))
Not:	Client.where.not(locked: true)	SELECT * FROM clients WHERE (clients.locked != 1)
Distinct:	Client.select(:name).distinct	SELECT DISTINCT name FROM clients
Limit	Client.limit(5)	SELECT * FROM clients LIMIT 5
Take:	client = Client.take(2)	SELECT * FROM clients LIMIT 2	Returns record without any implicit ordering. Returns nil if no record is found.
Offset:	Client.limit(5).offset(30)	SELECT * FROM clients LIMIT 5 OFFSET 30
Find or Create a New Object	Client.find_or_create_by!(first_name: 'Andy')	SELECT * FROM clients WHERE(clients.first_name = 'Andy') LIMIT 1 BEGIN INSERT INTO clients(created_at, first_name, updated_at) VALUES ('2011-08-30 05:22:57', 'Andy', '2011-08-30 05:22:57') COMMIT
Find or Initialize a New Object	nick = Client.find_or_initialize_by(first_name: 'Nick')
Find by SQL	Client.find_by_sql("SELECT * FROM clients INNER JOIN orders ON clients.id = orders.client_id ORDER BY clients.created_at desc")
Exists?	Client.exists?(1)
	Client.exists?(name: ['John', 'Sergei']
	Client.where(first_name: 'Ryan').exists?
Count	Client.count	SELECT count(*) AS count_all FROM clients
Average	Client.average("orders_count")
Minimum and Maximum	Client.minimum("age")		minimum/maximum value of a field
Sum	Client.sum("orders_count")		sum of a field
Ordering Results	Client.order(:orders_count, created_at: :desc)
	Client.order("orders_count ASC, created_at DESC")
Chaining ORDER BY	Client.order("orders_count ASC").order("created_at DESC")	SELECT * FROM clients ORDER BY orders_count ASC, created_at DESC

Joining Tables

# Join Through Defined Associations (Inner Join):
Category.joins(:articles)
Article.joins(:category, :comments)

   SELECT articles.* FROM articles   INNER JOIN categories ON articles.category_id = categories.id   INNER JOIN comments ON comments.article_id = articles.id

# Outer Joins:
Author.left_outer_joins(:posts).distinct.select('authors., COUNT(posts.) AS posts_count').group('authors.id')

   SELECT DISTINCT authors., COUNT(posts.) AS posts_count FROM "authors" LEFT OUTER JOIN posts ON posts.author_id = authors.id GROUP BY authors.id

# N + 1 queries problem: Always use .includes()
Article.includes(:category, :comments).where(comments: { visible: true })
Includes will decide between INNER JOIN eager_load (LOJ) or Seperate Queries

# Join Using Raw SQL:
Author.joins("INNER JOIN posts ON posts.author_id = authors.id AND posts.published = 't'")
SELECT authors.* FROM authors INNER JOIN posts ON posts.author_id = authors.id AND posts.published = 't'

# Retrieving filtered data from multiple tables: If you want to call order multiple times, subsequent orders will be appended to the first.
Person .select('people.id, people.name, comments.text') .joins(:comments) .where('comments.created_at > ?', 1.week.ago)

   SELECT people.id, people.name, comments.text FROM people INNER JOIN comments   ON comments.person_id = people.id WHERE comments.created_at > '2015-01-01'

# Retrieving specific data from multiple tables:
Person .select('people.id, people.name, companies.name') .joins(:company) .find_by('people.name' => 'John') # this should be the last

   SELECT people.id, people.name, companies.name FROM people INNER JOIN companies   ON companies.person_id = people.id WHERE people.name = 'John' LIMIT 1

Group By and Having

# Group By: Find a collection of the dates on which orders were created.
Order.select("date(created_at) as ordered_date, sum(price) as total_price").group("date(created_at)")
SELECT date(created_at) as ordered_date, sum(price) as total_price FROM orders GROUP BY date(created_at)

# Total of grouped items: To get the total of grouped items on a single query, call count after the group.
Order.group(:status).count
SELECT COUNT (*) AS count_all, status AS status FROM "orders" GROUP BY status)
# => { 'awaiting_approval' => 7, 'paid' => 12 }

# Having: SQL uses the HAVING clause to specify conditions on the GROUP BY fields. You can add the HAVING clause to the SQL fired by the Model.find by adding the having method to the find.
Order.select("date(created_at) as ordered_date, sum(price) as total_price"). group("date(created_at)").having("sum(price) > ?", 100)

   SELECT date(created_at) as ordered_date, sum(price) as total_price FROM orders GROUP BY date(created_at) HAVING sum(price) > 100

Pluck

Client.where(active: true).pluck(:id)	SELECT id FROM clients WHERE active = 1	# => [1, 2, 3]
Client.distinct.pluck(:role)	SELECT DISTINCT role FROM clients	# => ['admin', 'member', 'guest']
Client.pluck(:id, :name)	SELECT clients.id, clients.name FROM clients	# => [[1, 'David'], [2, 'Jeremy'], [3, 'Jose']]

pluck can be used to query single or multiple columns from the underlying table of a model.

pluck makes it possible to replace code like Client.select(:id).map { |c| c.id }

Unlike select, pluck directly converts a database result into a Ruby Array, without constructing ActiveRecord objects

Rails 5 ActiveRecord Queries Cheat Sheet (DRAFT) by dwapi

Active Record Queries

Joining Tables

Group By and Having

Pluck

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