Ecto - creating a dynamic where OR clause

ecto

#1

More Ecto questions! More madness!

The context: there’s a list of books that I want to filter with a dropdown…

The dropdown: looks something like (gt stands for greater than, lt stands for land tanks)…
def word_count_options do [ "0 - 5k": [gt: 0, lt: 5000], "5k - 30k": [gt: 5000, lt: 30000], "30k - 100k": [gt: 30000, lt: 100000], "100k - 200k": [gt: 100000, lt: 200000], "200k+": [gt: 200000, lt: 1000000000] ] end

The current code: almost works, but I would like to make this into ONE where clause with OR between the word count checks (so I can compose other queries that use where with this query without mucking up my intended filter logic)…

Enum.reduce(filters, query, fn filter, query -> 
options = Fic.word_count_options[String.to_existing_atom filter] 
from f in query, or_where: f.word_count > ^options[:gt] and f.word_count < ^options[:lt] 
end)

What’s the best path forward here? The “dynamic” keyword kinda seem like what I need, but I feel there’s a more straightforward way to handle this pattern…


#2

You should be able to use the dynamic macro to build all of the OR expressions and then interpolate it into the query at once: https://hexdocs.pm/ecto/Ecto.Query.html#dynamic/2


#3

Thx for the pointer Jose, ended up with something not so different from my original implementation:

dynamic = Enum.reduce(filters, false, fn filter, query -> 
    options = Fic.word_count_options[String.to_existing_atom filter] 
    dynamic([f], f.word_count > ^options[:gt] and f.word_count < ^options[:lt] or ^query)
end)

from f in query, where: ^dynamic