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Includes

  • ActiveRecord with includes ensures that all of the specified associations are loaded using the minimum possible number of queries.
  • So when querying a table for data with an associated table, both tables are loaded into memory.
@authors = Author.includes(:books).where(books: { bestseller: true } )

# this will print  results without additional db hitting
@authors.each do |author| 
  author.books.each do |book|
    puts book.title
  end
end
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  • Author.joins(:books).where(books: { bestseller: true } )will load only authors with conditions into memory without loading books.
  • Use joins when additional information about nested associations isn't required.
@authors = Author.joins(:books).where(books: { bestseller: true } )

# this will print results without additional queries
@authors.each { |author| puts author.name }

# this will print results with additional db queries
@authors.each do |author| 
  author.books.each do |book|
    puts book.title
  end
end
Clicking "Copy Code" button will copy the code into the clipboard - memory. Please paste(Ctrl+V) it in your destination. The code will get pasted. Happy coding from Wikitechy - ruby on rails tutorial - rails guides - ruby rails - rubyonrails - learn ruby on rails - team

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