How to combine multiple conditions in a find statement in Ruby on Rails

Posted on 12 April 2006

The best way for me to explain how to use multiple conditions is by example.

Basically I wanted to find all my departments that match a permalink passed from the url. The department must also match a particular category, also passed through the url.

My initial code looked like this:

category = params[:category]
department = params[:department]

@departments = Department.find(:all, :conditions => ["permalink = ?", department])
@department = @departments.find(:all, :conditions => ["category = ?", category])

The first problem is that I was writing find :all to find a single record to go into @department. When using find :all would return a hash (array) even if there is only one result row.

Secondly, I was incorrectly, and unecessarily, using Enumerable#find on @departments.

Enumerable#find requires 0 or 1 argument and 1 block, it doesn't work on arrays.

The final solution looked like this:

category = params[:category]
department = params[:department]

@department = Department.find(:first, :conditions => ["permalink = ? and category = ?", department, category])

find :all became find :first and the conditions statement was combined using the key word and. Easy when you know how!

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