class JobIteration::ActiveRecordCursor
Curious about how this works from the SQL perspective? Check “Pagination Done the Right way”: bit.ly/2Rq7iPF
Attributes
position[R]
reached_end[RW]
Public Class Methods
new(relation, columns = nil, position = nil)
click to toggle source
# File lib/job-iteration/active_record_cursor.rb, line 21 def initialize(relation, columns = nil, position = nil) columns ||= "#{relation.table_name}.#{relation.primary_key}" @columns = Array.wrap(columns) self.position = Array.wrap(position) raise ArgumentError, "Must specify at least one column" if columns.empty? if relation.joins_values.present? && !@columns.all? { |column| column.to_s.include?(".") } raise ArgumentError, "You need to specify fully-qualified columns if you join a table" end if relation.arel.orders.present? || relation.arel.taken.present? raise ConditionNotSupportedError end @base_relation = relation.reorder(@columns.join(",")) @reached_end = false end
Public Instance Methods
<=>(other)
click to toggle source
# File lib/job-iteration/active_record_cursor.rb, line 38 def <=>(other) if reached_end != other.reached_end reached_end ? 1 : -1 else position <=> other.position end end
next_batch(batch_size)
click to toggle source
# File lib/job-iteration/active_record_cursor.rb, line 58 def next_batch(batch_size) return nil if @reached_end relation = @base_relation.limit(batch_size) if (conditions = self.conditions).any? relation = relation.where(*conditions) end records = relation.uncached do relation.to_a end update_from_record(records.last) unless records.empty? @reached_end = records.size < batch_size records.empty? ? nil : records end
position=(position)
click to toggle source
# File lib/job-iteration/active_record_cursor.rb, line 46 def position=(position) raise "Cursor position cannot contain nil values" if position.any?(&:nil?) @position = position end
update_from_record(record)
click to toggle source
# File lib/job-iteration/active_record_cursor.rb, line 51 def update_from_record(record) self.position = @columns.map do |column| method = column.to_s.split(".").last record.send(method.to_sym) end end
Protected Instance Methods
conditions()
click to toggle source
# File lib/job-iteration/active_record_cursor.rb, line 79 def conditions i = @position.size - 1 column = @columns[i] conditions = if @columns.size == @position.size "#{column} > ?" else "#{column} >= ?" end while i > 0 i -= 1 column = @columns[i] conditions = "#{column} > ? OR (#{column} = ? AND (#{conditions}))" end ret = @position.reduce([conditions]) { |params, value| params << value << value } ret.pop ret end