Can anyone recommend a safe way/strategy to input some search conditions via URL parameters?

Hi,

Question - Can anyone recommend a safe way/strategy to input some
search conditions via URL parameters? So the requirements are:

[1] Only use URL parameters (e.g. key & value pair, where value is a string)
[2] At the server side convert these to a query string (i.e. the WHERE
clause in a SQL select statement)
[3] Need to "scrub" the inputs to avoid SQL injection
[4] Want to support more than basic column_name = value, so I need
also (here column_name would be the key):
    (a) column_name = true/false [for boolean]
    (b) NOT support - i.e. column_name != value
    (c) IS NOT NULL support, i.e. column_name IS NOT NULL
    (d) Range, i.e. column_name IS BETWEEN value1 AND value2
    (e) Some permutations of these, e.g. column name != true (so NOT
and a boolean)

Any suggestions? Anything I'm missing that solves this in Rails or
ActiveScaffold?

Background: The background is I'm using the ActiveScaffold (
http://activescaffold.com/) out of the box views. It has a server
side "conditions_from_params" that is supported & it passes the URL
parameters around well (e.g. then sorting buttons at columns continues
to work even through you've filtered down the list of rows). Here's
an extract of how I started to add some support to this for "range"
and "boolean", however I agree it's messy. I'm just looking for a
better way to do the below, plus then add on the other above-mentioned
support I have. Obviously I could just pass the exact parameters I
want for the WHERE clause in a query however then I assume there would
be SQL injection potential issues...

    # Builds search conditions by search params for column names. This
allows urls like "contacts/list?company_id=5".
    def conditions_from_params
      conditions = nil
      params.reject {|key, value| [:controller, :action,
:id].include?(key.to_sym)}.each do |key, value|
        next unless
active_scaffold_config.model.column_names.include?(key) # reject
keys that don't match table column in database

        if value.match(".*[.][.].*")
          # Range was specified
          elements = value.split('..')
          conditions = merge_conditions(conditions,
["#{active_scaffold_config.model.table_name}.#{key.to_s} BETWEEN
'#{elements[0]}' AND '#{elements[1]}' "])
        else
          # No range
          if ( value.upcase == "TRUE" || value.upcase == "FALSE")
            # Boolean
            conditions = merge_conditions(conditions,
["#{active_scaffold_config.model.table_name}.#{key.to_s} = ?",
value.upcase == "TRUE" ? true : false])
          else
            # Non Boolean
            conditions = merge_conditions(conditions,
["#{active_scaffold_config.model.table_name}.#{key.to_s} = ?", value])
          end
        end

      end
      conditions
    end

Thanks