Class: RailsStackview::DbWindowFetcher

Inherits:
Object
  • Object
show all
Defined in:
app/fetch_adapters/rails_stackview/db_window_fetcher.rb

Overview

Fetches from the stackview_call_numbers table with ActiveRecord

  • Assumes a windowing ‘search_type:loc_sort_order` in stackview, which sends query=[X TO Y] in params.

  • Additionally assumes we get an ‘origin_sort_key` in params, which will used as the “zero point” for stackview’s query ranges. It must be an actual normalized sort_key – if it does not exist in the DB, we’ll just browse from that point in sort order though.

    We use this origin_sortkey to try and avoid very deep offsets in our SQL, which get expensive, although if the user pages a LOT they can still get there. If this is not good enough, we’ll have to contribute features to stackview to provide alternate windowing based on sortkeys alone. 

Create a path to the StackviewDataController using 'lc' call_number_type,
which uses this fetcher, specifying the origin_sort_key as a query param:

   stackview_data_path("lc", :origin_sort_key => some_sort_key)

Instance Method Summary collapse

Instance Method Details

#fetch(params) ⇒ Object 



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# File 'app/fetch_adapters/rails_stackview/db_window_fetcher.rb', line 25

def fetch(params)
  @origin_sort_key = params["origin_sort_key"]
  @sort_key_type   = params["sort_key_type"] || "lc"

  unless @origin_sort_key.present?
    raise ArgumentError, "`origin_sort_key` param required, specifying where to start the browse"
  end

  (first, last)  = RailsStackview.parse_query_range(params["query"])
  unless first < last
    raise ArgumentError, "beginning of range must be less than end: #{params["query"]}"
  end


  # Fetch the AR models, then turn em into hashes, which include all
  # columns in the db, excluding some we don't want. 
  #
  # Plus we need to turn our single creator into an array, cause
  # that's what stackview wants.
  results = fetch_records(first, last).collect do |record|
    record.attributes.except('id').reject {|k, v| v.blank? }.
      merge("creator" => (record["creator"].present? ? [record['creator']] : record['creator']))
  end

  # Mark the thing at 0 index as origin:true, so it can be auto-selected
  # by browser. 
  if (first..last).cover?(0)
    origin_index = [first.abs, results.length - 1].min
    results[origin_index]["is_origin_item"] = true
  end

  return results
end

#fetch_records(first, last) ⇒ Object

Returns ActiveRecord StackviewCallNumber objects.



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# File 'app/fetch_adapters/rails_stackview/db_window_fetcher.rb', line 61

def fetch_records(first, last)
  if first >= 0 && last >= 0 # all positive
    positive_fetch(first, last)
  elsif first < 0 && last >= 0# cross zero-boundary
    # have to do half first and half last
    negative_fetch(first, -1) + positive_fetch(0, last)
  else # all negative
    negative_fetch(first, last)
  end
end

#negative_fetch(first, last) ⇒ Object 



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# File 'app/fetch_adapters/rails_stackview/db_window_fetcher.rb', line 79

def negative_fetch(first, last)
  StackviewCallNumber.where("sort_key < ?", @origin_sort_key).
    where(:sort_key_type => @sort_key_type).
    order("sort_key DESC").
    offset(last.abs - 1).limit(last - first + 1).
    reverse
end

#positive_fetch(first, last) ⇒ Object 



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# File 'app/fetch_adapters/rails_stackview/db_window_fetcher.rb', line 72

def positive_fetch(first, last)
  StackviewCallNumber.where("sort_key >= ?", @origin_sort_key).
    where(:sort_key_type => @sort_key_type).
    order("sort_key ASC").
    offset(first).limit(last - first + 1)
end