From: Arlen Cuss <celtic@...>
Date: 2008-03-08T21:14:10+09:00
Subject: Re: Creating a search

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Hi,

Firstly, I'll make a note that this is the Ruby mailing list. You probably
won't get many Rails-specific answers here, as we all-too-often are
bombarded with requests for help with Rails specifics which most of us may
prefer not to know. Here's their list address:
http://groups.google.com/group/rubyonrails-talk.

Secondly, we're still a nice bunch.

On Sat, Mar 8, 2008 at 9:39 PM, Tom Ha <tom999@gmx.net> wrote:

> - But since submitting the search page/form with only *some* (not all)
> fields filled in (or check boxes checked, or radio buttons clicked,
> etc.) would generate some "empty" values in the key/value pairs in
> "params[:search]", the generated search statement would be wrong because
> for example a condition saying " 'gender' => nil/empty " could be added.
> - So, only key/value pairs which have a value that's not empty should
> generate the "condition" code.




>      @searchresults = User.find(:all, :conditions => {
>        i=0        # <= I get the error for this line

Conditions is actually a Hash, or expecting a Hash, and indeed, this syntax
is trying to construct a hash. Instead, it looks like you're writing a block
instead - which can't work.
Here's something to think about:
>> {:a => nil, :b => 42}.reject {|k,v| v.nil?}
=> {:b=>42}
>>

Hash#reject takes a block, returning a new hash, excluding the values for
which the block returned true. (i.e. true, since we say yes to `rejecting')
It looks like you tried to embed a function/set of methods into the hash
above (:conditions => {stmt; stmt;...}), but we can't do that. Instead, try
something more functional:
    params[:search].reject {|key, val| val.nil?}.map {|k, v| "#{key.inspect}
=> #{value.inspect}"}.join(", ")
This does pretty much everything you try to do here with the loop, and it's
a bit more concise. Here's how to read it:

params[:search].reject {|key, val| val.nil?}
  This returns a new hash without any key/val-pair where the value is `nil'.
Replace `val.nil?' with your own condition that returns `true' when you
don't that value.
.map {|k, v| "#{key.inspect} => #{value.inspect}"}
  This goes through each key/val-pair in the hash, and returns an array.
Here's an example of the output:
    >> {:a => nil, :b => 42}.map {|k,v| "#{k.inspect} => #{v.inspect}"}
    => [":b => 42", ":a => nil"]
    >>
.join(", ")
  This does what your loop was trying to do, though slightly more concisely.
Array#join takes one argument and uses that as the `separator', stringing
the elements together with that between.
    >> [":b => 42", ":a => nil"].join ", "
    => ":b => 42, :a => nil"
    >>

Hope this helps.

Arlen

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