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Olá

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Building an ORM with ARel Walking up the AS(Tree) @vipulnsward, @_cha1tanya

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Vipul @vipulnsward && Prathamesh @_cha1tanya

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RubyIndia.org

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podcast.rubyindia.org

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Indian Ruby Conferences RubyConfIndia Garden City Ruby Conf DeccanRubyConf Do visit India!

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Building an ORM with ARel Walking up the (AS)Tree @vipulnsward, @_cha1tanya

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Build our own ORM - Why?

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Object-relational mapping (ORM, O/RM, and O/R mapping) in computer science is a programming technique for converting data between incompatible type systems in object- oriented programming languages. This creates, in effect, a "virtual object database" that can be used from within the programming language.

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Active Record “An object that wraps a row in a database table or view, encapsulates the database access, and adds domain logic on that data.”

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Components ● Database connection ● Query Generator ● Attribute Access ● Typecasting

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SQL torm_development=# select * from posts; id | name | content | author | subject -----+-------------+---------+------------+--------- 332 | RGenGC| Restricted Generation Garbage Collection | GorbyPuff | How does RGenGC work? (1 row)

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Object Post: id: 332, name: ‘RGenGC’, subject: ‘How does RGenGC work?’ content: ‘Restricted Generation Garbage Collection’ author: ‘GorbyPuff’

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Object Post: id(int): 332, name(string): ‘RGenGC’, subject(string): ‘How does RGenGC work?’ content(string): ‘Restricted Generation Garbage Collection’ author(string): ‘GorbyPuff’

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What? post = Post.new subject: 'What is RGenCG?' post.save first_post = Post.find(1) puts first_post.subject #=> 'What is RGenCG?'

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How? class Post < Torm::Model … end

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Role of ARel

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ARel ● Relational Algebra for Ruby ● ARel is a SQL AST manager for Ruby ● Can generate complex SQL queries ● Adapts to multiple databases

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ARel Components ● AST ● Visitors ● Managers

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ORM Database ARel

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Engine ● Provide information to ARel/ Attributes Access ● Column / Table structure ● Database Adapter ● Data Type Mappings

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Engine Skeleton

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Database Connection

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Columns

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Schema Cache

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Tests

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Attributes ● Data Types ● Casting from / to database types ● Attribute Maps for table ● Accessors for a model

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Types ● Types ● TypeMap ● Attribute ● AttributeSet

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Attribute Accessors ● Readers ● Writes ● Initializer

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Database Statements ● create ● update ● save ● destroy

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Querying ● find ● count ● where ● delete_all ● ...

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Summary ● Database Connection ● Creating columns/ Schema cache ● Attribute Types/ Type casting ● Attributes and accessors ● Database statements ● Querying

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Other ● Associations ● Migrations ● Callbacks ● Validations ● ...

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Obrigado! gh: prathamesh-sonpatki/torm @vipulnsward @_cha1tanya