Find by many conditions in Ruby on Rails - ruby-on-rails

Question

There is a search action in RoR that can handle some params e.g.:
params[:name] # can be nil or first_name
params[:age] # can be nil or age
params[:city] # can be nil or country
params[:tag] # can be nil or country
The model name is Person. It also has_many :tags.
When finding persons I need like to AND all the conditions that are present. Of course, it not rational and not DRY.
What I tried to do:
conditions = []
conditions << [ "name like ?", params[:name]+"%" ] if params[:name].present?
conditions << [ "age = ?", params[:age] ] if params[:age].present?
conditions << [ "city = like ?", params[:city]+"%" ] if params[:city].present?
#persons = Person.all(:conditions => conditions )
#What about tags? How do include them if params[:tag].present?
Of course, I want my code to be DRY. Now it's not. Even more, it will cause an exception if params[:age] and params[:name] and params[:city] are not present.
How can I solve? And how do I include tags for persons filtered by tag.name=params[:tag] (if params[:tag].present?) ?

Answer 1

You should do something like this:
lets say filters parameters include this:
filters = {
:name_like => "Grienders",
:age_equal => 15
}
Now you define methods for each
class Person
def search_with_filters(filters)
query = self.scoped
filters.each do |key, values|
query = query.send(key, values)
end
return query
end
def name_like(name)
where("name like ?", name)
end
def age_equal(age)
where(:age => age
end
end
Do you see the method search_with_filters will be the "controlling" method that will take a set of query conditions (name_like, age_equal, etc...) and pass them out to matching method name using the send method, and along with that we also pass the condition which will be the parameter of the method.
The reason why this way is good is because you can scale to any number of conditions (your filter lets say get huge) and also the code is very clean because all you have to do is populate your filters parameter. The method is very readable and very modular and also easy to test

Answer 2

To include the tags condition in your query:
if params[:tag].present?
#persons = Person.all(:conditions => conditions).includes(:tags).where("tags.name = ?", params[:tag])
else
#persons = Person.all(:conditions => conditions)
end
As for there error you are getting when params[:age] .. is not present - This is very strange because it is supposed to return false incase the key is not set in params. Could you please paste the error you are getting?

Answer 3

I would work extensively with scopes for this. Starting with default scope, merge other scopes based on conditions.
Write scopes (or class methods):
class Person << AR::Base
...
NAME_PARTS = ['first_name', 'last_name']
scope :by_name, lambda { |q| where([NAME_PARTS.join(' LIKE :q OR ') + ' LIKE :q', { :q => "%#{q}%" }]) }
scope :by_email, lambda { |q| joins(:account).where(["accounts.email LIKE :q", { :q => "%#{q}%" }]) }
scope :by_age, where(["people.age = ?", q])
scope :tagged, lambda { |q| joins(:tags).where(["tags.name LIKE :q", { :q => "%#{q}%" }]) }
end
Refer:
Scopes in Rails 3
Scopes overhaul section in How Rails 3 Makes Your Life Better
Now, merge the scopes only when the condition is met. As I understand your condition, is the value for a particular search item is nil (like, age is not given), do not search for that scope.
...
def search(object)
interested_fields = ['name', 'age', 'email', 'tags']
criteria = object.attributes.extract!(*interesting_fields) # returns { :age => 20, ... }
scope = object.class.scoped
build(criteria).each do |k, v|
scope = scope.send(k.to_sym, v)
end
scope.all
end
# This method actually builds the search criteria.
# Only keep param which has value and reject the rest.
def build(params)
required = ['name', 'age', 'email', 'tags']
params.delete_if { |k, v| required.include?(k) && v.blank? }
params
end
...
Refer:
extract!