How to simplify big conditions - ruby-on-rails

Question

I have five dropdowns, and I need to put conditions on each of them. My code is:
def search(search, compare, year, rain_fall_type)
if search == 'All'
if rain_fall_type == 'All'
all
else
if year == 'All'
if rain_fall_type == "None"
where('Sector = ? OR Sector = ? OR Sector = ?', "Primary", 'Secondary', 'Tertiary').order('id')
else
# all
where(Sector: rain_fall_type).order('id')
end
else
if rain_fall_type == "All"
order("#{year} ")
elsif rain_fall_type == "None"
where('Sector = ? OR Sector = ? OR Sector = ?', "Primary", 'Secondary', 'Tertiary').order('id')
else
where(Sector: rain_fall_type).order("#{year} ")
end
end
# where(Year: year).order("#{rain_fall_type} ")
end
elsif compare != "None"
if year == 'All'
where('Sector = ? OR Sector = ?', rain_fall_type, compare).order(:id)
else
where('Sector = ? OR Sector = ?', rain_fall_type, compare).order(:id)
end
else
if rain_fall_type == 'All'
all.order('id')
else
if year == 'All'
if rain_fall_type == "None"
where('Sector = ? ', search).order('id')
else
where('Sector = ? ', rain_fall_type).order('id')
end
else
if rain_fall_type == "None"
if search == "All"
where('Sector = ? ', search).order('id')
else
where('Sector = ? ', search).order('id')
end
else
# all
where('Sector = ? ', rain_fall_type).order('id')
end
end
end
end
end
It has many if and else. I am trying to minimise the conditions. What can be the best way to shrink this code? Someone suggested that I should use switch case instead. Should I use it? If so, how?

Answer 1

You can use a guard statement which is basically return something if some_condition?. This only doable in specific scenarios (where one of the condition is executing a single statement:
Bad example:
if condition?
do_something
else
do_something_else
end
This could be written as:
return do_something if condition?
do_something_else
This will give you less code branching.
Also, another recommendation is to call another method with more conditions instead of nesting conditions in one single shot.
Bad example:
if condition?
if condition_two?
do_something_two
else
do_something
end
else
do_something_else
end
This could be written as:
if condition?
call_another_method
else
do_something_else
end
def call_another_method
if condition_two?
do_something_two
else
do_something
end
end
An example from your code could be:
if rain_fall_type == 'All'
all
else
if year == 'All'
if rain_fall_type == "None"
where('Sector = ? OR Sector = ? OR Sector = ?', "Primary", 'Secondary', 'Tertiary').order('id')
else
# all
where(Sector: rain_fall_type).order('id')
end
else
if rain_fall_type == "All"
order("#{year} ")
elsif rain_fall_type == "None"
where('Sector = ? OR Sector = ? OR Sector = ?', "Primary", 'Secondary', 'Tertiary').order('id')
else
where(Sector: rain_fall_type).order("#{year} ")
end
end
end
That could be converted to:
return all if rain_fall_type == 'All'
if year == 'All'
return where('Sector = ? OR Sector = ? OR Sector = ?', "Primary", 'Secondary', 'Tertiary').order('id') if rain_fall_type == "None"
where(Sector: rain_fall_type).order('id')
else
return order("#{year} ") if rain_fall_type == "All"
return where('Sector = ? OR Sector = ? OR Sector = ?', "Primary", 'Secondary', 'Tertiary').order('id') if rain_fall_type == "None"
where(Sector: rain_fall_type).order("#{year} ")
end
I hope this could help :)
NOTE: This is to answer the original question of How to simplify big conditions?. But the original post is not following Rails/Ruby way of doing search and filters and not making a good use of scopes.

Answer 2

This is probably the best explanation of how you should set this up.
class Product < ActiveRecord::Base
# custom_scope_1
scope :status, -> (status) { where status: status }
# custom_scope_2
scope :location, -> (location_id) { where location_id: location_id }
# custom_scope_3
scope :search, -> (name) { where("name like ?", "#{name}%")}
end
def index
#products = Product.where(nil) # creates an anonymous scope
#products = #products.status(params[:status]) if params[:status].present?
#products = #products.location(params[:location]) if params[:location].present?
#products = #products.search(params[:search]) if params[:search].present?
end
This can be cleaned up further by...
def index
#products = Product.where(nil)
filtering_params(params).each do |key, value|
#products = #products.public_send(key, value) if value.present?
end
end
private
# A list of the param names that can be used for filtering the Products
def filtering_params(params)
params.slice(:status, :location, :search)
end
This method uses ruby meta-programming to loop through parameters and dynamically call predefined scopes on a model
You can move this code into a module and include it into any model that supports filtering
app/models/concerns/filterable.rb
module Filterable
extend ActiveSupport::Concern
module ClassMethods
def filter(filtering_params)
results = self.where(nil)
filtering_params.each do |key, value|
results = results.public_send(key, value) if value.present?
end
results
end
end
end
app/models/product.rb
class Product
include Filterable
...
end
app/controllers/product_controller.rb
def index
#products = Product.filter(params.slice(:status, :location, :search))
end
You now have filtering and searching of your models with one line in the controller and one line in the model

Answer 3

First of all, some of your logic doesn't make sense:
def search(search, compare, year, rain_fall_type)
if search == 'All'
if rain_fall_type == 'All'
all
else
# rain_fall_type != 'All'
if year == 'All'
if rain_fall_type == "None"
where('Sector = ? OR Sector = ? OR Sector = ?', "Primary", 'Secondary', 'Tertiary').order('id')
else
where(Sector: rain_fall_type).order('id')
end
else
# in rain_fall_type != 'All' branch, so meaningless 'if'
if rain_fall_type == "All"
order("#{year} ")
elsif rain_fall_type == "None"
where('Sector = ? OR Sector = ? OR Sector = ?', "Primary", 'Secondary', 'Tertiary').order('id')
else
where(Sector: rain_fall_type).order("#{year} ")
end
end
end
elsif compare != "None"
# both are same, so meaningless 'if'
if year == 'All'
where('Sector = ? OR Sector = ?', rain_fall_type, compare).order(:id)
else
where('Sector = ? OR Sector = ?', rain_fall_type, compare).order(:id)
end
else
# search != 'All'
if rain_fall_type == 'All'
all.order('id')
else
if year == 'All'
if rain_fall_type == "None"
where('Sector = ? ', search).order('id')
else
where('Sector = ? ', rain_fall_type).order('id')
end
else
if rain_fall_type == "None"
# in search != 'All' branch, so meaningless 'if'
# AND both are same, so again meaningless 'if'
if search == "All"
where('Sector = ? ', search).order('id')
else
where('Sector = ? ', search).order('id')
end
else
where('Sector = ? ', rain_fall_type).order('id')
end
end
end
end
end
There's more like that and I won't point it all out because we're throwing all that if stuff out, anyway.
Ultimately, we're going to defer the querying to the end of the method, like this:
def search(search, compare, year, rain_fall_type)
...
#query = all
#query = #query.where(Sector: #sectors) if #sectors
#query = #query.order(#order) if #order
#query
end
That way, you take all of your where and order statements, and do them only once at the end. That saves a lot of typing right there. See the comment from muistooshort for why (Sector: #sectors) works.
So, the trick is setting #sectors and #order. First, I'm going to assign the input variables to instance variables because I like it like that (and to avoid confusion between the variable #search and the method search):
def search(search, compare, year, rain_fall_type)
#search, #compare, #year, #rain_fall_type = search, compare, year, rain_fall_type
...
#query = all
#query = #query.where(Sector: #sectors) if #sectors
#query = #query.order(#order) if #order
#query
end
Now, this answer is going on too long already, so I won't drag you through all the gorey details. But, adding in a couple of helper methods (sectors_to_use, and order_to_use) and substituting them in for #sectors and #order, you basically end up with this:
def search(search, compare, year, rain_fall_type)
#search, #compare, #year, #rain_fall_type = search, compare, year, rain_fall_type
#query = all
#query = #query.where(Sector: sectors_to_use) if sectors_to_use
#query = #query.order(order_to_use) if order_to_use
#query
end
private
def sectors_to_use
return [#rain_fall_type, #compare] if #search != 'All' && #compare != 'None'
unless #rain_fall_type == 'All'
if #rain_fall_type == 'None'
#search == 'All' ? ['Primary', 'Secondary', 'Tertiary'] : [#search]
else
[#rain_fall_type]
end
end
end
def order_to_use
return nil if (#search == 'All') && (#rain_fall_type == 'All')
return #year if (#search == 'All') && !(#year == 'All')
return :id
end
That's less than half the lines of code, over a thousand fewer characters, and a whole lot fewer ifs.