何时何地聚合或执行RESTful Rails API中的数据计算

Question

I was wondering if there is a general way one should go about aggregating data or performing calculations on it (eg grabbing ten random lines of a movie script, or multiplying ten product prices by each other) in Rails or in MVCs in general. Specifically I'm attempting to do the first example (10 lines of a movie script) in my application.

I'm using Rails 5.2+. What I've tried so far is making an instance method getRandomLines in my ScriptLinesController . But I'm not sure whether I should instead be using the show method and aggregating the data on the client-side, or if I should put the method in the model ScriptLine

I've tested the following route using Postman and it works, but it seems like the wrong way to go about it:

#My routes.rb:
Rails.application.routes.draw do
  # For details on the DSL available within this file, see http://guides.rubyonrails.org/routing.html

  get 'script_lines/test', to: 'script_lines#getRandomLines'

end

My controller looks like this:

class ScriptLinesController < ApplicationController
  def index
    render json: ScriptLine.all
  end

  def show
    scriptLine = ScriptLine.find_by(id: params[:id])

    render json: scriptLine
  end

  def getRandomLines
    numLines=rand(0..9)
    nineLines = []
    numLines.times do
      id_num = rand(1..ScriptLine.last.id)
      nineLines << ScriptLine.find_by(id: id_num)
    end

    render json: nineLines[0]
  end
end

My model looks like this:

class ScriptLine < ApplicationRecord
  validates :line_number, presence:true

  belongs_to :script
end

Finally my schema looks like this:

  create_table "script_lines", force: :cascade do |t|
    t.string "line_number"
    t.string "line"
    t.bigint "script_id"
    t.index ["script_id"], name: "index_script_lines_on_script_id"
  end

So in sum, is creating methods in the controller and specifying routes to those methods the right way to aggregate/perform calculations on data in a RESTful manner? In particular I'm wondering if the 7 standard RESTful routes are the only routes allowed, or if you can have ad-hoc routes for manipulating data that comply with REST principles.

This is my first question, so apologies in advance if it's asking too much or too vague, will modify accordingly.

Answer 1

This is a pretty broad design question so I'm just going to give a list of general pointers to think about:

• A major component of RESTful web service design is picking the right resources, which do not need to correspond directly with the tables in your database. It's totally appropriate to invent new resources (usually but now always with a corresponding class in models/ ) that map more naturally to what the client is looking for.
• In general I'd recommend performing aggregations on the server side at the database level (or via some other data-storage mechanism like a pre-computed cache if even the database is too slow)
• If you're using a relational database, it can be useful to define views that perform the aggregation ( https://www.postgresql.org/docs/11/sql-createview.html ). Then you can create an activerecord model that references the view
• It's generally not worth creating controller methods that are named differently from what's in your routes file. In your example I'd just have a new action random at /script_lines/random and then a controller method random .
• Depending on how truly "RESTful" you want to be, you may or may not need be working in a codebase where it's acceptable to define non-standard controller actions and it might or might not be acceptable for a GET endpoint to return random results like this (both of these can break the strict definition of REST). Check out this answer: RESTful web service to get random number verb for some more context.

Personally, if I wasn't overly concerned with RESTful-ness, I'd add a new action to the ScriptLinesController like this:

class ScriptLinesController < ApplicationController
  def random
    num_lines = rand(0..9)
    render json: ScriptLine.order("RANDOM()").limit(num_lines)
  end
end

As the random function got more complicated over time I'd consider moving it to the ScriptLine model. If even more complexity got added that was all logically related to the concept of "Collection of random script lines" I'd move that code out to a separate other model and create a new controller.