Spelunking through Arel

Arel is the underlying API that ActiveRecord uses to construct SQL queries. But how does it actually work?

Transcript

1. Code Spelunking through Arel Adam Lassek @alassek (with Pry & friends) wrcochran @ Flickr
2. ActiveRecord Arel Database User
3. Records PLZ ActiveRecord Arel Database User
4. DSL ActiveRecord Arel Database User
5. AST ActiveRecord Arel Database User
6. Visit AST ActiveRecord Arel Database User
7. SQL ActiveRecord Arel Database User
8. SQL ActiveRecord Arel Database User
9. Tuples ActiveRecord Arel Database User
10. Records ActiveRecord Arel Database User
11. Arel is a Framework Framework
12. Arel is a Framework Framework
13. Abstract Syntax Tree Arel is an
14. Arel is an AST users = Arel::Table.new(:users) users.project(users[Arel.star])
16. Arel is an AST users = Arel::Table.new(:users) users.project(users[Arel.star])
17. Arel is an AST users = Arel::Table.new(:users) users.project(users[Arel.star]) .where(users[:name].matches('adam%'))
18. Arel is an AST users = Arel::Table.new(:users) users.project(users[Arel.star]) .where(users[:name].matches('adam%')) .where(users[:created_at].between(Date.new(2016, 1, 1)..Date.today))
19. Arel is an AST users = Arel::Table.new(:users) users.project(users[Arel.star]) .where(users[:name].matches('adam%')) .where(users[:created_at].between(Date.new(2016, 1, 1)..Date.today)) .order(users[:created_at].desc) .take(100)
20. Visitor Pattern Arel is a
21. Consider a compiler that represents programs as abstract syntax trees. It will need to perform operations on abstract syntax trees for "static semantic" analyses like checking that all variables are defined. It will also need to generate code. So it might define operations for type- checking, code optimization, flow analysis, check for variables being assigned values before they're used, and so on. Moreover, we could use the abstract syntax trees for pretty- printing, program restructuring, code instrumentation, and computing various metrics of a program. ”
22. SQL Visitor SELECT "users".* FROM "users" WHERE "users"."name" ILIKE 'adam%' AND "users"."created_at" BETWEEN '2016-01-01' AND '2016-09-01' ORDER BY "users"."created_at" DESC LIMIT 100
23. Dot Visitor GraphViz https://github.com/glejeune/Ruby-Graphviz http://www.graphviz.org/
26. LIVE CODING!!!
27. Thanks!