2

I am working with an API that provides bus arrival data. For every request, I get back (among other things) a list of which routes serve the stop in question. For example, if the list includes result for bus route #1, 2, and 5, then I know that those serve this stop.

I have a many-to-many relationship set up between Route and Stop, and I want to dynamically check and update these associations on every request. There is no "master list" of which routes serve which stops, so this seems like the best way to get this data.

I believe that the way I'm doing it now is very inefficient:

# routes is an array of [number, destination] that I build while iterating over the data
routes.uniq.each do |route|
  number      = route[0]
  destination = route[1]

  r = Route.find_by_number_and_destination(number, destination)

  if !r
    r = Route.new :number => number, :destination => destination
    r.save
  end

  # I have to check if it already exists because I can't find a way
  # to create a uniqueness constraint on the join table with 2 foreign keys
  r.stops << stop unless r.stops.include? stop
end

Basically, I have to do 2 things for every route I find: 1) Create it if it doesn't already exist, 2) Add a relationship to the current stop if it doesn't already exist.

Is there a better way to do this, for example by getting a bunch of the data in memory and doing some of the processing on the app server side, in order to avoid the multitude of database calls I'm currently doing?

4

3 回答 3

1

如果我做对了，你（应该）有 2 个模型。Route 模型和 Stop 模型。

以下是我如何定义这些模型：

class Route < ActiveRecord::Base
  has_and_belongs_to_many :stops
  belongs_to :stop, :foreign_key => 'destination_id'
end

class Stop < ActiveRecorde::Base
  has_and_belongs_to_many :routes
end

以下是我设置表格的方式：

create_table :routes do |t|
  t.integer :destination_id
  # Any other information you want to store about routes
end

create_table :stops do |t|
  # Any other information you want to store about stops
end

create_table :routes_stops, :primary_key => [:route_id, :stop_id] do |t|
  t.integer :route_id
  t.integer :stop_id
end

最后，这是我要使用的代码：

# First, find all the relevant routes, just for caching.
Route.find(numbers)

r = Route.find(number)
r.destination_id = destination
r.stops << stop

这应该只使用几个 SQL 查询。

于 2008-09-07T15:35:05.840 回答
1

试试这个宝石： https ://github.com/seamusabshere/upsert

文档说它比 find_or_create_by 快 80%

于 2012-06-21T18:54:00.990 回答
0

可能有一种清理停止呼叫的好方法，但是假设我正确地描绘了路线的结构，这会清理很多。

routes.uniq.each do |number, destination|

  r = Route.find_or_create_by_number_and_destination(route[0], destination)

  r.stops << stop unless r.stops.include? stop

end
于 2012-03-06T03:43:06.583 回答