Support AR::Relation (add AR::Relation#using_readonly/using_writable)

[winebarrel]

The connection used depends on the timing of relation evaluation.

SwitchPoint.readonly_all!
Article.with_writable { p Article.all }  # Read from db-blog-master
p Article.with_writable { Article.all }  # Read from db-blog-slave

I extend the AR::Relation to add the following method:

Article.using_readonly.first # Read from db-blog-slave
Article.where(id: 1).using_writable.update_all(title: 'new title') # Write to db-blog-master

Please review 🙏

[eagletmt]

I tried this branch and found a strange behavior.

[5] pry(#<RSpec::ExampleGroups::SwitchPointRelation::WithReadonly::UsingTake>)> Book.all.to_a
=> [#<Book:0x00000000049eeef0 id: 99>]  # OK. It connects to readonly DB.
[6] pry(#<RSpec::ExampleGroups::SwitchPointRelation::WithReadonly::UsingTake>)> Book.using_writable.to_a
=> [#<Book:0x0000000004999d10 id: 1>]   # OK. It connects to writable DB.
[7] pry(#<RSpec::ExampleGroups::SwitchPointRelation::WithReadonly::UsingTake>)> rel = Book.using_writable; rel.using_readonly.to_a
=> [#<Book:0x0000000004948a78 id: 99>]  # OK. It connects to readonly DB.
[8] pry(#<RSpec::ExampleGroups::SwitchPointRelation::WithReadonly::UsingTake>)> rel = Book.using_writable; rel.to_a; rel.using_readonly.to_a
=> [#<Book:0x0000000004911e60 id: 1>]   # NG. Why does it connect to writable DB?

Is the last behavior intentional?

[winebarrel]

Is the last behavior intentional?

Sorry, it is a bug.
Fixed 02335b4

[eagletmt]

"extension is only supported in Rails 4.0 or higher"

[winebarrel]

Thanks! fixed 22b0a39

[eagletmt]

def exec_queries(*)

[winebarrel]

Thanks! fixed 1afdd17