class Pupa::Processor
An abstract processor class from which specific processors inherit.
Attributes
Public Class Methods
Adds a scraping task to Pupa.rb.
Defines a method whose name is identical to ‘task_name`. This method selects a method to perform the scraping task using `scraping_task_method` and memoizes its return value. The return value is a lazy enumerator of objects scraped by the selected method. The selected method must yield objects to populate this lazy enumerator.
For example, ‘MyProcessor.add_scraping_task(:people)` defines a `people` method on `MyProcessor`. This `people` method returns a lazy enumerator of objects (presumably Person
objects in this case, but the enumerator can contain any object in the general case).
In ‘MyProcessor`, you would define an `scrape_people` method, which must yield objects to populate the lazy enumerator. Alternatively, you may override `scraping_task_method` to change the method selected to perform the scraping task.
The ‘people` method can then be called by transformation and import tasks.
@param [Symbol] task_name a task name @see Pupa::Processor#scraping_task_method
# File lib/pupa/processor.rb, line 95 def self.add_scraping_task(task_name) self.tasks += [task_name] define_method(task_name) do ivar = "@#{task_name}" if instance_variable_defined?(ivar) instance_variable_get(ivar) else instance_variable_set(ivar, Yielder.new(&method(scraping_task_method(task_name)))) end end end
@param [String] output_dir the directory or Redis address
(e.g. `redis://localhost:6379`) in which to dump JSON documents
@param [Boolean] pipelined whether to dump JSON documents all at once @param [String] cache_dir the directory or Memcached address
(e.g. `memcached://localhost:11211`) in which to cache HTTP responses
@param [Integer] expires_in the cache’s expiration time in seconds @param [Integer] value_max_bytes the maximum Memcached item size @param [String] memcached_username the Memcached username @param [String] memcached_password the Memcached password @param [String] database_url the database URL @param [Boolean] validate whether to validate JSON documents @param [String] level the log level @param [String,IO] logdev the log device @param [Hash] faraday_options Faraday
initialization options @param [Hash] options criteria for selecting the methods to run
# File lib/pupa/processor.rb, line 36 def initialize(output_dir, pipelined: false, cache_dir: nil, expires_in: 86400, value_max_bytes: 1048576, memcached_username: nil, memcached_password: nil, database_url: 'mongodb://localhost:27017/pupa', validate: true, level: 'INFO', logdev: STDOUT, faraday_options: {}, options: {}) @store = DocumentStore.new(output_dir, pipelined: pipelined) @client = Client.new(cache_dir: cache_dir, expires_in: expires_in, value_max_bytes: value_max_bytes, memcached_username: memcached_username, memcached_password: memcached_password, level: level, logdev: logdev, faraday_options: faraday_options) @connection = Connection.new(database_url) @logger = Logger.new('pupa', level: level, logdev: logdev) @validate = validate @options = options @report = {} end
Public Instance Methods
Yields the object to the transformation task for processing, e.g. saving to disk, printing to CSV, etc.
@param [Object] an object @note All the good terms are taken by Ruby: ‘return`, `send` and `yield`.
# File lib/pupa/processor.rb, line 69 def dispatch(object) Fiber.yield(object) end
Dumps scraped objects to disk.
@param [Symbol] task_name the name of the scraping task to perform @return [Hash] the number of scraped objects by type @raises [Pupa::Errors::DuplicateObjectIdError]
# File lib/pupa/processor.rb, line 112 def dump_scraped_objects(task_name) counts = Hash.new(0) @store.pipelined do send(task_name).each do |object| counts[object._type] += 1 dump_scraped_object(object) end end counts end
Retrieves and parses a document with a GET request.
@param [String] url a URL to an HTML document @param [String,Hash] params query string parameters @return a parsed document
# File lib/pupa/processor.rb, line 51 def get(url, params = {}) client.get(url, params).body end
Saves scraped objects to a database.
@raises [TSort::Cyclic] if the dependency graph is cyclic @raises [Pupa::Errors::UnprocessableEntity] if an object’s foreign keys or
foreign objects cannot be resolved
@raises [Pupa::Errors::DuplicateDocumentError] if duplicate objects were
inadvertently saved to the database
# File lib/pupa/processor.rb, line 130 def import @report[:import] = {} objects = deduplicate(load_scraped_objects) object_id_to_database_id = {} if use_dependency_graph?(objects) dependency_graph = build_dependency_graph(objects) # Replace object IDs with database IDs in foreign keys and save objects. dependency_graph.tsort.each do |id| object = objects[id] resolve_foreign_keys(object, object_id_to_database_id) # The dependency graph strategy only works if there are no foreign objects. database_id = import_object(object) object_id_to_database_id[id] = database_id object_id_to_database_id[database_id] = database_id end else size = objects.size # Should be O(n²). If there are foreign objects, we do not know all the # edges in the graph, and therefore cannot build a dependency graph or # derive any evaluation order. # # An exception is raised if a foreign object matches multiple documents # in the database. However, if a matching object is not yet saved, this # exception may not be raised. loop do progress_made = false objects.delete_if do |id,object| begin resolve_foreign_keys(object, object_id_to_database_id) resolve_foreign_objects(object, object_id_to_database_id) progress_made = true database_id = import_object(object) object_id_to_database_id[id] = database_id object_id_to_database_id[database_id] = database_id rescue Pupa::Errors::MissingDatabaseIdError false end end break if objects.empty? || !progress_made end unless objects.empty? raise Errors::UnprocessableEntity, "couldn't resolve #{objects.size}/#{size} objects:\n #{objects.values.map{|object| JSON.dump(object.foreign_properties)}.join("\n ")}" end end # Ensure that fingerprints uniquely identified objects. counts = {} object_id_to_database_id.each do |object_id,database_id| unless object_id == database_id (counts[database_id] ||= []) << object_id end end duplicates = counts.select do |_,object_ids| object_ids.size > 1 end unless duplicates.empty? raise Errors::DuplicateDocumentError, "multiple objects written to same document:\n" + duplicates.map{|database_id,object_ids| " #{database_id} <- #{object_ids.join(' ')}"}.join("\n") end end
Retrieves and parses a document with a POST request.
@param [String] url a URL to an HTML document @param [String,Hash] params query string parameters @return a parsed document
# File lib/pupa/processor.rb, line 60 def post(url, params = {}) client.post(url, params).body end
Private Instance Methods
Builds a dependency graph.
@param [Hash] objects a hash of scraped objects keyed by ID @return [DependencyGraph] the dependency graph
# File lib/pupa/processor.rb, line 330 def build_dependency_graph(objects) DependencyGraph.new.tap do |graph| objects.each do |id,object| graph[id] = [] # no duplicate IDs object.foreign_keys.each do |property| value = object[property] if value graph[id] << value end end end end end
For each object, map its ID to the ID of its duplicate, if any.
@param [Hash] objects a hash of scraped objects keyed by ID @return [Hash] a mapping from an object ID to the ID of its duplicate
# File lib/pupa/processor.rb, line 294 def build_losers_to_winners_map(objects) inverse = {} objects.each do |id,object| (inverse[object.to_h.except(:_id)] ||= []) << id end {}.tap do |map| inverse.values.each do |ids| ids.drop(1).each do |id| map[id] = ids[0] end end end end
Removes all duplicate objects and re-assigns any foreign keys.
@param [Hash] objects a hash of scraped objects keyed by ID @return [Hash] the objects without duplicates
# File lib/pupa/processor.rb, line 269 def deduplicate(objects) losers_to_winners = build_losers_to_winners_map(objects) # Remove all losers. losers_to_winners.each_key do |key| objects.delete(key) end # Swap the IDs of losers for the IDs of winners. objects.each do |id,object| object.foreign_keys.each do |property| value = object[property] if value && losers_to_winners.key?(value) object[property] = losers_to_winners[value] end end end objects end
Dumps an scraped object to disk.
@param [Object] object an scraped object @raises [Pupa::Errors::DuplicateObjectIdError]
# File lib/pupa/processor.rb, line 219 def dump_scraped_object(object) type = object.class.to_s.demodulize.underscore name = "#{type}_#{object._id.gsub(File::SEPARATOR, '_')}.json" if @store.write_unless_exists(name, object.to_h) info {"save #{type} #{object.to_s} as #{name}"} else raise Errors::DuplicateObjectIdError, "duplicate object ID: #{object._id} (was the same objected yielded twice?)" end if @validate begin object.validate! rescue JSON::Schema::ValidationError => e warn {e.message} end end end
@param [Object] object an object
# File lib/pupa/processor.rb, line 387 def import_object(object) inserted, id = connection.save(object) @report[:import][object._type] ||= Hash.new(0) if inserted @report[:import][object._type][:insert] += 1 else @report[:import][object._type][:update] += 1 end id end
Loads a scraped object from its properties.
@param [Hash] properties the object’s properties @return [Object] a scraped object @raises [Pupa::Errors::MissingObjectTypeError] if the scraped object is
missing a `_type` property.
# File lib/pupa/processor.rb, line 256 def load_scraped_object(properties) type = properties['_type'] || properties[:_type] if type type.camelize.constantize.new(properties) else raise Errors::MissingObjectTypeError, "missing _type: #{JSON.dump(properties)}" end end
Loads scraped objects from disk.
@return [Hash] a hash of scraped objects keyed by ID
# File lib/pupa/processor.rb, line 241 def load_scraped_objects {}.tap do |objects| @store.read_multi(@store.entries).each do |properties| object = load_scraped_object(properties) objects[object._id] = object end end end
Resolves an object’s foreign keys from object IDs to database IDs.
@param [Object] an object @param [Hash] a map from object ID to database ID @raises [Pupa::Errors::MissingDatabaseIdError] if a foreign key cannot be
resolved
# File lib/pupa/processor.rb, line 350 def resolve_foreign_keys(object, map) object.foreign_keys.each do |property| value = object[property] if value if map.key?(value) object[property] = map[value] else raise Errors::MissingDatabaseIdError, "couldn't resolve foreign key: #{property} #{value}" end end end end
Resolves an object’s foreign objects to database IDs.
@param [Object] object an object @param [Hash] a map from object ID to database ID @raises [Pupa::Errors::MissingDatabaseIdError] if a foreign object cannot
be resolved
# File lib/pupa/processor.rb, line 369 def resolve_foreign_objects(object, map) object.foreign_objects.each do |property| value = object[property] if value.present? foreign_object = ForeignObject.new(value) resolve_foreign_keys(foreign_object, map) document = connection.find(foreign_object.to_h) if document object["#{property}_id"] = document['_id'] else raise Errors::MissingDatabaseIdError, "couldn't resolve foreign object: #{property} #{value}" end end end end
Returns the name of the method - ‘scrape_<task_name>` by default - that would be used to perform the given scraping task.
If you would like to change this default behavior, override this method in a subclass. For example, you may want to select a method according to the additional ‘options` passed from the command-line to the processor.
@param [Symbol] task_name a task name @return [String] the name of the method to perform the scraping task
# File lib/pupa/processor.rb, line 211 def scraping_task_method(task_name) "scrape_#{task_name}" end
If any objects have unresolved foreign objects, we cannot derive an evaluation order using a dependency graph.
@param [Hash] objects a hash of scraped objects keyed by ID @return [Boolean] whether a dependency graph can be used to derive an
evaluation order
# File lib/pupa/processor.rb, line 315 def use_dependency_graph?(objects) objects.each do |id,object| object.foreign_objects.each do |property| if object[property].present? return false end end end true end