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Building an ORM with Arel
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Prathamesh Sonpatki
August 22, 2014
Technology
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Building an ORM with Arel
Talk given at Madison Ruby 2014 with @vipulnsward
Prathamesh Sonpatki
August 22, 2014
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Transcript
Building an ORM with ARel Walking up the AS(Tree) @vipulnsward,
@_cha1tanya
Vipul @vipulnsward && Prathamesh @_cha1tanya
None
26 Hours
48 Hours
None
None
None
RubyIndia.org
None
podcast.rubyindia.org
Indian Ruby Conferences RubyConfIndia Garden City Ruby Conf DeccanRubyConf Do
visit India!
Building an ORM with ARel Walking up the (AS)Tree @vipulnsward,
@_cha1tanya
None
Build our own ORM - Why?
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.
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.”
Components • Database connection • Query Generator • Attribute Access
• Typecasting
SQL torm_development=# select * from posts; id | name |
content | author | subject -----+-------------+---------+------------+--------- 332 | RGenGC| Restricted Generation Garbage Collection | GorbyPuff | How does RGenGC work? (1 row)
Object Post: id: 332, name: ‘RGenGC’, subject: ‘How does RGenGC
work?’ content: ‘Restricted Generation Garbage Collection’ author: ‘GorbyPuff’
Object Post: id(int): 332, name(string): ‘RGenGC’, subject(string): ‘How does RGenGC
work?’ content(string): ‘Restricted Generation Garbage Collection’ author(string): ‘GorbyPuff’
What? post = Post.new subject: 'What is RGenCG?' post.save first_post
= Post.find(1) puts first_post.subject #=> 'What is RGenCG?'
How? class Post < Torm::Model … end
Role of ARel
ARel • Relational Algebra for Ruby • ARel is a
SQL AST manager for Ruby • Can generate complex SQL queries • Adapts to multiple databases
ARel Components • AST • Visitors • Managers
ORM Database ARel
Engine • Provide information to ARel/ Attributes Access • Column
/ Table structure • Database Adapter • Data Type Mappings
Engine Skeleton
Database Connection
Columns
Schema Cache
Tests
None
Attributes • Data Types • Casting from / to database
types • Attribute Maps for table • Accessors for a model
Types • Types • TypeMap • Attribute • AttributeSet
Attribute Accessors • Readers • Writes • Initializer
Database Statements • create • update • save • destroy
Querying • find • count • where • delete_all •
...
Summary • Database Connection • Creating columns/ Schema cache •
Attribute Types/ Type casting • Attributes and accessors • Database statements • Querying
Other • Associations • Migrations • Callbacks • Validations •
...
Thank You! gh: prathamesh-sonpatki/torm @vipulnsward @_cha1tanya