Merge nested params via link_to - ruby-on-rails-3

Question

I'm using nested params (via ransack nested as q) alongside normal params to build links on a page and am having trouble with getting the two to play nicely when I try and merge the nested params with the other params.
For example if I have:
{"freq"=>"weekly", "loan_amount"=>"350000",
"q"=>{"lowEquity_true"=>"1", "s"=>"rate asc"}}
and try and build a link to change the param "lowEquity_true" with
rates_url(params[:q].merge(:lowEquity_true => '0'))
then I end up with the new params below, which looks like its updated q but dropped the rest of the params.
{"lowEquity_true"=>"0", "s"=>"rate asc"}
If I instead try to merge q & merge into the other params it doesn't update q, and just merges what was in q into the other params instead
rates_url(params[:q].merge(:lowEquity_true => '0').merge(params))
{"freq"=>"weekly", "loan_amount"=>"350000", "lowEquity_true"=>"0",
"q"=>{"lowEquity_true"=>"1", "s"=>"rate asc"},
"s"=>"rate asc"}
I've tried all sorts of various combinations and don't appear to be getting anywhere so am sure that I'm missing something basic!

Answer 1

You are doing it wrong.
Let me explain with an example :
params = {:a => 1, :b => 2, :q => {:x => 24, :y => 25}}
At this point, params[:q] is
{:x=>24, :y=>25}
If I do,
params[:q].merge(:x => 99)
then my params[:q] will become
{:x=>99, :y=>25}
and this is what you are supplying as an argument to rates_url(params[:q].merge(:lowEquity_true => '0'))
that's why only {"lowEquity_true"=>"0", "s"=>"rate asc"} is passed to rates_url as parameters.
Now, if you do something like
params[:q].merge(:x => 99).merge(params)
then params[:q].merge(:x => 99) gives you {:x=>99, :y=>25} and then it merges {:x=>99, :y=>25} into the original params {:a => 1, :b => 2, :q => {:x => 24, :y => 25}}
, so this results into
{:x=>99, :y=>25, :a=>1, :b=>2, :q=>{:x=>24, :y=>25}}
Now, let me explain you what you should do :-
You params is
{"freq"=>"weekly", "loan_amount"=>"350000",
"q"=>{"lowEquity_true"=>"1", "s"=>"rate asc"}}
So, you should do :
params[:q].merge!(:lowEquity_true => '0')
rates_url(params)
That's it
I hope you khow the difference between merge and merge! :-
merge! is destructive, it will modify the original paramter where as merge will not unless you take it in a variable and use it.
Alternatively, if you want to do the same thing stated above in a single line then, just do
rates_url(params.merge!(:q => {:lowEquity_true => '0', "s"=>"rate asc"}))
OR
rates_url(params.merge(:q => params[:q].merge(:lowEquity_true => '0')))