Over on the Rails mailing list, Rafał Komorowski asks How to programatically build :contitions with elegance?
His problem is a form with four conditions. Each may be applied, but any or all of them may be set to “All”.
The brute force way of doing this would be:
1 class SearchController < ApplicationController 2 def search 3 case 4 when params[:cond1] && params[:cond2] 5 conditions = ['cond1 = ? AND cond2 = ?', 6 params[:cond1], params[:cond2]] 7 when params[:cond1] 8 conditions = ['cond1 = ?', 9 params[:cond1]] 10 when params[:cond2] 11 conditions = ['cond2 = ?', 12 params[:cond2]] 13 end 14 15 @results = Model.find(:all, :conditions => conditions) 16 end 17 end
Note that in this case, you have to pay attention to the order in which you evaluate your conditions. If you put params[:cond1] before params[:cond1] && params[:cond2], and params[:cond1] is true, Ruby will only evaluate the params[:cond1] branch.
Instead, I prefer to do this:
1 class SearchController < ApplicationController 2 def search 3 conditions = ['1=1'] 4 5 conditions << 'cond1 = :cond1' if params[:cond1] 6 conditions << 'cond2 = :cond2' if params[:cond2] 7 8 @results = Model.find(:all, 9 :conditions => [conditions.join(' AND '), params]) 10 end 11 end
Note how I initialize the conditions array: ['1=1']. This is to prevent a problem later on when Rails evaluates the conditions option to find . If we leave the array empty, Rails will append the WHERE empty condition, generating something like this:
1 SELECT * FROM models WHERE
The database backend will complain with a syntax error.
This discussion aside, I believe this is clear and concise code. Ain’t Ruby fun ?
