Rails database Query Solution for N + 1 queries

Schema.rb

Activerecord::schema.define (version:20150203032005) do create_table"addresses", Force:true do |t|T.integer"client_id"t.string"Street"t.string"Postcode"T.datetime"Created_at"T.datetime"Updated_at"End Create_table"Clients", Force:true do |t|t.string"name"t.string"Gender"T.datetime"Created_at"T.datetime"Updated_at"End Create_table"infos", Force:true do |t|T.integer"address_id"t.string" History"T.datetime"Created_at"T.datetime"Updated_at"EndEnd

Client.rb

class Client < activerecord::base  has_one:addressend

Address.rb

class Address < activerecord::base  belongs_to:client  has_many:infosend

Info.rb

class Address < activerecord::base  belongs_to:client  has_many:infosend

Client.all

  Client Load (0.4MS)  

Address.all

Info.all

　　

Solution for N + 1 queries

Clients = Client.limit (2) Clients.each do |client|   Puts Client.address.postcodeend 

The resulting SQL statement is:

Select "Clients". * FROM "clients" = #<  

and

Clients = Client.includes (: address). Limit (2) Clients.each do |client|   Puts Client.address.postcodeend 

The resulting SQL statement is:

Client Load (0.5ms)  Select  "Clients". * FROM "clients"  LIMIT 2  Address Load (0.4ms)  Select " Addresses ". * from" addresses "  WHERE" addresses "." Client_id "in (1, 2  

Load multiple associations on demand

Clients =|client|     puts Client.address.infos.first.historyend

Generated SQL statement:

Address Load (0.3ms)  select  "Addresses". * from "addresses"  WHERE "addresses". " client_id "=? LIMIT 1  [["client_id", 1]]  Info Load (0.3ms)  select  "Infos". * from "infos"  WHERE "Infos". " address_id "=?  ORDER by "Infos". " ID "ASC LIMIT 1  [[" address_id ", 1]]1110  address Load (0.1ms)  select  " Addresses ". * FROM" addresses " C13/>where "addresses". " client_id "=? LIMIT 1  [["client_id", 2]]  Info Load (0.1ms)  select  "Infos". * from "infos"  WHERE "Infos". " address_id "=?  ORDER by "Infos". " ID "ASC LIMIT 1  

The client and address are has_one relationships, address and info are has_many relationships, and want to load resources once so that the client can get info via address using the following statement:

Clients = Client.includes (address:: infos)

Generated SQL statement:

Client Load (0.4ms)  Select "Clients". * FROM "clients"  Address Load (0.5ms)  Select "Addresses". * FROM " Addresses "  WHERE" addresses "." Client_id "in (1, 2)  Info Load (0.3ms)  select" Infos ". * FROM" infos "  

　　

Clients.each do |c|     puts C.address.infos.first.historyend

Output:

1110
2110

Rails database Query Solution for N + 1 queries