Introduction to Arel

Arel fundamentals

Transcript

1. Introduction to Arel
   

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2. Bruno Sutic

   Rails & Javascript developer

   

   Ideal Project Group, Chicago
   github.com/bruno-

   @brunosutic
   

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3. What is Arel?
   • github.com/rails/arel
   • “Simplifies generation of complex SQL”

   You write Ruby, out comes the SQL
   • dependency of ActiveRecord
   • can be used together with ActiveRecord
   

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4. How I learned about Arel?
   • credit: Janko Marohnic
   • used Arel to optimize a feature on a project
   

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5. Demo to get you interested :)
   

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6. Prerequisites for the
   examples
   • ‘Customer’ is an ActiveRecord model
   • Arel api for a column:

   Customer.arel_table[:name]
   • A “convention”:

   class Customer

   def self.[](column)

   arel_table[column]

   end

   end
   Customer[:name]
   

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7. Basic example
   • ActiveRecord

   Customer.where(name: variable)
   • Arel

   Customer.where(Customer[:name].eq(variable))
   

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8. A bit more useful example
   • ActiveRecord

   Customer.joins(:sales)

   .where(“sales.price” => variable)

   

   or

   

   Customer.joins(:sales)

   .where(sales: { price: variable })
   • Arel

   Customer.joins(:sales)

   .where(Sale[:price].eq(variable))
   

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9. SQL comparisons example
   • ActiveRecord

   Customer.where(“credits > ?”, credits_variable)
   • Arel

   Customer.where(

   Customer[:credits].gt(credits_variable)

   )
   • All comparison operators:

   gt, lt, gteq, lteq
   

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10. OR condition example
    • ActiveRecord

    Customer.where(“credits > ? OR credits < ?”, var1, var2)
    • Arel

    Customer.where(

    Customer[:credits].gt(var1).or(

    Customer[:credits].lt(var2)

    )

    )
    

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11. Complex conditions example
    • ActiveRecord

    Customer.where(

    “credits > ? OR (name = ? AND credits < ?)”, var1, var2, var3

    )
    • Arel

    Customer.where(

    Customer[:credits].gt(var1).or(

    Customer[:name].eq(var2).and(

    Customer[:credits].lt(var3)

    )

    )

    )
    

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12. LIKE example
    • ActiveRecord

    Customer.where(“name LIKE ?”, “%#{variable}%”)
    • Arel

    Customer.where(Customer[:name].matches(“%#{variable}%”))
    

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13. Other features
    • support for all SQL ‘join’ types
    • SQL literals
    • writing only a part of a bigger query as SQL
    • example: CASE statement
    

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14. Benefits of using Arel
    • pure Ruby, nicer looking code
    • proper code highlighting
    • ruby exceptions
    • completely avoids SQL injection
    

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15. Arel resources
    • github repo:

    https://github.com/rails/arel
    • great speech:

    https://www.youtube.com/watch?v=ShPAxNcLm3o
    • source code walkthrough:

    https://www.youtube.com/watch?v=EJ6b_2S9Ids
    • examples from this talk:

    https://gist.github.com/bruno-/5964403476c791331c49
    

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16. Questions?
    

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