Rails and Kaminari pagination with certain priority per page - mysql

Question

I have complex query that I wrote partly as MySQL database view and partly as ActiveRecord logic in Rails. Each record has it's own priority from 0-4 where 4 is top priority.
I'm using Kaminari for pagination and I'm wondering if there's a way to show per page sets of records with some extra rules:
Show all #4 priority rows on first page
Take per_page number and show priority 3 with this formula: 0.3*per_page
Then do the same with priority 2
Then if all 3 steps didn't produced 100% of per_page show the rest with priority 0 and 1
How could I achieve result by using Rails. Or is it better to implement it directly in SQL?
Here is sample of my db view:
select *
from (
select
s.id as source_id,
'Spree::Store' as source_type,
(case when (s.created_at >= curdate() - INTERVAL DAYOFWEEK(curdate())+6 DAY AND s.created_at < curdate() - INTERVAL DAYOFWEEK(curdate())-1 DAY)
then
'new'
else
'old'
end) as sub_type,
1 as priority,
s.created_at as created_at,
s.updated_at as updated_at,
null as owner_id
from spree_stores as s
where s.image_id is not NULL and s.is_hidden = false
union
select
e.id as source_id,
'Event' as source_type,
(case
when (e.status = 1 and e.is_featured is false)
then
'live'
when (e.is_featured = true)
then
'featured'
else
case when (e.created_at >= curdate() - INTERVAL DAYOFWEEK(curdate())+6 DAY AND e.created_at < curdate() - INTERVAL DAYOFWEEK(curdate())-1 DAY)
then
'new'
else
'old'
end
end) as sub_type,
(case
when (e.status = 1 or e.is_featured is true)
then
3
else
1
end) as priority,
e.created_at as created_at,
e.updated_at as updated_at,
null as owner_id
from events as e
where e.status >= 1 and e.expires_at >= curdate()
union
select
o.id as source_id,
'Spree::Order' as source_type,
(case when (o.created_at >= curdate() - INTERVAL DAYOFWEEK(curdate())+6 DAY AND o.created_at < curdate() - INTERVAL DAYOFWEEK(curdate())-1 DAY)
then
'new'
else
'old'
end) as sub_type,
1 as priority,
o.created_at as created_at,
o.updated_at as updated_at,
o.user_id as owner_id
from spree_orders as o
where o.user_id is not NULL and o.share is true and o.state = 'complete' and o.completed_at is not NULL
union
select
p.id as source_id,
'Spree::Product' as source_type,
(case when (p.created_at >= curdate() - INTERVAL DAYOFWEEK(curdate())+6 DAY AND p.created_at < curdate() - INTERVAL DAYOFWEEK(curdate())-1 DAY)
then
'new'
else
'old'
end) as sub_type,
1 as priority,
p.created_at as created_at,
p.updated_at as updated_at,
null as owner_id
from spree_products as p
join spree_variants as sv on (sv.product_id = p.id and sv.is_master = true)
join spree_assets as sa on (sa.viewable_id = sv.id and sa.viewable_type = 'Spree::Variant')
where p.deleted_at is NULL
group by p.id
) a
order by priority desc, created_at desc;
This is the result I'm getting (only few lines not all 200 results):

Answer 1

This sounds like more complex logic than Kaminari is built for and probably worth doing it yourself. Kaminari is certainly convenient for knocking out a quick pagination UI, but it really doesn't add a huge amount of value compared to rolling your own solution. You might be able to hack it to fit your needs, but that's probably more headache than just doing it yourself.
I'm also a little skeptical the complex algorithm you're wanting is really going to benefit users. Only you know that for sure, but you might want to consider a simple "score" or "rank" column and then just use Kaminari with a query sorted by score desc.