Stockboy

Stockboy helps you receive and unpack data onto your shelves. It provides a DSL for configuring data processing pipelines. You might consider using it to synchronize data exported from external sources, as part of an ETL workflow, or migrating your own data from legacy systems.

Full documentation available at rdoc.info/gems/stockboy

Goals

Stockboy was originally developed at Guestfolio to help synchronize data from many external systems that export periodic reports in various incompatible ways. Each data source might vary orthogonally on:

• Where the data resides: whether a SOAP service, sent to an IMAP mailbox, an FTP server, or simply a local file.
• How the data is formatted: whether CSV, Excel, XML, JSON, or some other obscure format.
• How the records are structured: what fields are included, and how they are named.
• What format the fields are: such as different date formats (DMY vs. MDY), whether names are "first, last", or what do do with missing values.
• Which records to process: selecting whether records are incomplete, or valid and needing to be added, updated or deleted.

The goal of Stockboy is to provide a clean, but flexible DSL for declaring these configurations and keeping them external to your application, letting your app standardize on handling one common interface for the many different sources.

Usage

Following your defined job template (see below), a Stockboy job will process incoming data into abstract "records". Stockboy leaves it up to your application to decide what to do with them.

job = Job.define("my_template")

job.process
records = job.records            #=> Hash of records sorted by filter key
other   = job.unfiltered_records #=> Array of records unmatched by a filter
all     = job.all_records        #=> Array

Yielding processed results to a block is also supported:

job.process do |records, unfiltered|
  records[:updated].each  { |r| YourModel.create(r.attributes) }
  records[:no_data].each  { |r| log.warn "No data for #{r.id}" }
  unfiltered_records.each { |r| log.info "Skipping: #{r.raw_hash}" }
end

Records

Each record exposes both the source values and the mapped output values according to your defined mapping. Typically the mapped fields should correspond to the actual attributes on your application models. These can be accessed as individual methods, or by converting the record to a hash.

record.input["RawEmailField"] # => "ARTHUR@EXAMPLE.COM"
record.output.email           # => "arthur@example.com"

record.to_hash or record.attributes
#=> {check_in: #<Time ...>, location_id: 123, first_name: "Arthur", ...}

record.to_model(YourModel) or YourModel.new(record.attributes)
#=> #<YourModel ...>

Record Hash

Record attributes are hashed from the output values. This means that records can be compared as equal:

record1.attributes
#=> {last_name: "Robin", first_name: "Hood", location: "Sherwood Forest"}

record2.attributes
#=> {first_name: "Robin", last_name: "Hood", location: "Sherwood Forest"}

record1 == record2
#=> true

Or reduced to a unique set:

job.records[:new_signups].uniq

Because of its consistency, the object hash on Stockboy records is suitable as an identity key, e.g. for caching.

record.hash
#=> "0d320adc4cae992a1d0a6c6e4f1aff11"

Note: If you rely on this feature for record uniqueness, it’s up to you to ensure that the same input values are always translated to consistently produce the same output values. Translator blocks that manipulate values based on data external to the record (for example time), would produce records with different hash values.

Job Template DSL

Stockboy job templates are defined in Ruby but are simple and abstract enough to be considered more configuration than code. They should reside in the template load path for easy loading. Once defined, job templates are parsed and loaded at runtime, so they can be added or updated separately without needing to restart a long-running process, e.g. Rails or Sidekiq.

Writing a job template requires you to declare three parts:

Example

# config/stockboy_jobs/my_template.rb

provider :ftp do
  host       "example.com"
  username   "mystore"
  password   "123456"
  file_name  "dailyreport-*.csv"
  file_pick  :first
end

repeat do |inputs, provider|
  0.upto 12 do |m|
    provider.file_dir = "reports/#{Date.today << 12-m}"
    inputs << provider
  end
end

attributes do
  email       from: 'RawEmailAddress'
  first_name  as: proc{ |r| r['Full-Name'].split(' ').first }
  last_name   as: proc{ |r| r['Full-Name'].split(' ').last }
  birthdate   as: [:time]
  score       as: [:integer, :default_zero]
end

filter(:invalid_email) do |input, _|
  not(input.email.include?('@') or input['EmailAddress'] == '')
end

filter(:missing_code) do |_, output|
  output.product_code.nil?
end

Looking at the parts of this template:

1. Get it with a provider

The provider block describes the connection parameters for finding and fetching data, which is returned as a raw string blob. It can handle some complexity to determine which file to pick from an email attachment or FTP directory, for example.

Fetching paginated data

If the provider requires multiple queries to fetch all the data (e.g. http ?page=1 query params or a list of files), you can use an optional repeat block to specify how to iterate over the data source, and when to stop. Although it's possible to process each page as an individual job, the repeat option is useful when you need to have all the data in hand before making downstream processing decisions such as purging records that are not in the data set.

repeat do |inputs, http_provider|
  loop do
    inputs << http_provider
    break if http_provider.data.split("\n").size < 100
    http_provider.query["page"] += 1
  end
end

For each iteration, increment the provider settings and push it onto the list of inputs. (This uses an Enumerator to yield each iteration's data before processing the next one, so it should be memory-efficient for long series of data sets.)

See: File, FTP, HTTP, IMAP, SOAP

2. Parse it with a reader

The reader block describes how to turn the raw string from the provider into sets of fields. This extracts the raw data tokens, which we can then map to our application's domain.

See: CSV, Fixed-Width, Spreadsheet, XML

3. Collect it into attributes

The attributes block is the main part of the template definition. This describes which fields to extract from the parsed data, and how to represent each value in the output record. The output attributes are defined by calling the attribute's name plus two options:

from:

When the field name from the source doesn't match the desired attribute name, this option should be used to name the correct field to read from the source record.

as:

By default, attributes are returned as the original raw string data value, but translators can be applied to change the input to any format. Acceptable options include a symbol for a built-in translator (e.g. :date) or any Proc or callable object responding to call(source_record).

Translator blocks can access record fields as either:

Indexes for raw input fields	Methods for final attribute names
->(r){ r['RawEmail'].downcase }	->(r){ r.email.downcase }

Since the entire record context is passed, you can combine multiple input fields into one attribute (e.g. combining date plus time). You can also define two attributes that extract different data from the same field, e.g. splitting a full name field into first and last.

Translations are applied in order when given as an array. Since translators are designed to handle invalid data, they will catch exceptions and return a nil so it's a good idea to have default values at the end of the chain.

ignore:

If a field needs to be omitted when exporting to hash (to avoid downstream clients clobbering existing values with nil), specify the option with a callable object or a symbol that can be called against the output field value:

title ignore: true
email ignore: ->(r) { not r.email.include?("@") }
score ignore: :zero?

The callable object receives the whole record context like when translating with the "as" option.

Built-in attribute translators:

• :boolean Common true/false strings to True or False (e.g. '1'/'0' or 't'/'f')
• :date ISO-8601 or common strings to Date (e.g. "2012-12-21" or "Dec 12, 2012")
• :uk_date Date strings from UK format to Date (e.g. "DD/MM/YY")
• :us_date Date strings from US format to Date (e.g. "MM/DD/YY")
• :decimal Numeric strings to BigDecimal (e.g. prices)
• :integer Numeric strings to Integer integers
• :string Clean strings with leading/trailing whitespace trimmed
• :or_empty Returns "" for blank values
• :or_nil Returns nil for blank values
• :or_zero Returns 0 for blank values

Attributes can be defined in a block as described, or added individually as attribute :name.

Debugging attribute translations

If an attribute can't be translated the default behaviour is to return nil instead of raising an error that would terminate the entire job. There is a global config option to handle these errors as needed, perhaps for debugging:

Stockboy.configuration.translation_error_handler = proc { |error|
  puts "Failed attribute: #{error.key.inspect}"
  puts "Input: #{error.record.raw_hash.inspect}"
  puts error.backtrace
}

The object yielded to the error handler is an exception with additional properties:

• key: The name of the attribute key that was attempted to translate
• record: The original record context with all the input fields for inspection

It can simply be raised if preferred.

4. Funnel it with filters

Filters are optional, but they are very helpful for funneling the data into your workflow. For example, you may need to partition records for different handling based on a status field.

Filters are applied in the order that they are declared. The first filter that returns true when traversing a record will capture it. Records that fall through all the filters without matching anything are considered "unfiltered".

job.process
job.records[:update]   #=> Array
job.unfiltered_records #=> Array
job.all_records        #=> Array

Filters can inspect records either pre- or post-translation. Often you just need to look at the raw input parameters, but it's also possible to get the output values from the second block parameter:

filter(:example) do |input, output|
  input["RawEmailAddress"] =~ /gmail/ or output.bounce_count > 1
end

5. Trigger it with actions

Also optional, triggers let you define an action in the job template context that can be called from your application. This lets you separate your app interface from the implementation details of each data source.

A typical use case might be to clean up stale data after a successful import:

on :cleanup do |job, timestamp|
  next unless job.processed?
  job.provider.client do |ftp|
    ftp.put(StringIO.new(timestamp.to_s), "LAST_RUN")
  end
  job.provider.delete_data # deletes the last matching file used
end

The action blocks receive the job instance, and any additional arguments when called via job.trigger(:cleanup, Time.now) or simply job.cleanup(Time.now).

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Installation

Add gem 'stockboy' to your Gemfile and run bundle install.

Supported on Ruby 1.9+.

Configuration

When loaded under a Rails app, Stockboy will look for config/stockboy.rb for self-configuration if it's present.

Template Load Paths

Template load paths are intended for storing your defined job templates for different data sources. (config/stockboy_jobs/ is the default when loaded in a Rails app; else it must be defined.)

Stockboy.configuration do |config|
  config.template_load_paths = ['config/job_imports', 'config/log_imports']
end

Register Custom Providers / Readers

Beyond the standard providers (:ftp, :soap, etc.) and readers (:csv, :xml), you can register your own for fetching or parsing data from different sources. (Contributions welcome.)

Stockboy::Readers.register :m3u, PlaylistReader
Stockboy::Providers.register :gopher, GopherProvider
Stockboy::Translations.register :product_code, YourProductCodeTranslator

See the Reader, Provider, and Translator for details on implementing your own custom classes.

Development

Contributions and pull requests are welcome.

bundle install
bundle exec rake # runs tests