Talk dada em um meetup de Ruby em Florianópolis sobre queries avançadas utilizando active record e arel

1. Advanced queries with
RubyOnRails
How to not fight with database queries

3. ActiveRecord
- Map models to table
- Simple queries with exact values
- CRUD
- Queries with few tables
- Advanced queries
- Queries with multiple tables
- OR
- Queries without exact values

4. How to do those queries and be happy?

5. Always use scopes on models
Don't do Book.where(title: 'Harry Potter') outside a model
Always create a scope and calls it like Book.by_title('Harry Potter')

6. Don't write sql strings in scopes
Harder to maintain and understand
Can introduce bugs when you use it joining with other tables
May not work if you change your database

7. Examples

9. select * from books where category = 'drama';
All Books with category equal 'drama'
Book.where(category: 'drama')
Book.where(arel_table[:category].eq('drama'))

10. select * from books
where books.category = 'drama' or books.title = 'Harry Potter'
Books from drama category or title is Harry Potter
Book.where('category = ? or title = ?', category, title)
Book.where(arel_table[:category].eq(category).or(arel_table[:title].eq(title)))

11. Book.where(arel_table[:category].eq('drama')
.or(arel_table[:title].matches('Harry Potter')
.or(arel_table[:description].matches('Harry Potter'))))
select * from books
where books.category = 'drama' or books.title like '%Harry Potter%' or books.description like
'%Harry Potter%'
Books from drama category or has Harry Potter on title or description
Book.where("category = ? or title like ? or description like ?",
'drama', '%Harry Potter%', '%Harry Potter%')

12. Books published in 2016
Book.where(published_at: '2016-01-01'.to_date..'2016-12-31'.to_date)
select * from books
where books.published_at between '2016-01-01' and '2016-12-31'

13. select * from books
inner join publishers on publishers.id = books.publisher_id
where books.category = 'drama' and publishers.country = 'Brazil'
Books from drama category and publisher from Brazil
Book.joins(:publisher)
.where(category: 'Drama')
.merge(Publisher.where(country: 'Brazil'))
Book.joins(:publisher).where(category: 'Drama').where('publishers.country = ?', 'Brazil')
Book.joins(:publisher).where(category: 'Drama').where(publishers: { country: 'Brazil' })

14. select * from books
where books.pages_count < 10
Books that has less than 10 pages
Book.where(arel_table[:pages_count].lt(10))
Book.where('pages_count < ?', 10)

15. select * from authors
where authors.country != 'Brazil'
Authors that are not from Brazil
Author.where(arel_table[:country].not_eq('Brazl'))
Author.where.not(country: 'Brazil')

16. select * from books
left outer join publishers on publishers.id = books.publisher_id
where publishers.id is null or publishers.country = 'Brazil'
Books unpublished or publisher from Brazil
publishers = Publisher.arel_table
books = Book.arel_table
Book.joins(books.join(publishers, Arel::Node::OuterJoin)
.on(books[:publisher_id].eq(publishers[:id]).join_sources)
.where(publishers[:country].eq('Brazil').or(publishers[:id].eq(nil))
Book.joins('left outer join publishers on publishers.id = books.publisher_id)
.where('publishers.id = null or publishers.country = ?', 'Brazil')
publishers = Publisher.arel_table
books = Book.arel_table
Book.includes(:publisher)
.references(:publisher)
.where(publishers[:country].eq('Brazil').or(publishers[:id].eq(nil))

18. https://github.com/rails/arel
https://github.com/jplethier/queries-example
http://blog.carbonfive.com/2016/11/16/rails-database-best-practices/