Module: DatastaxRails::Batches

Included in:
Base, Relation
Defined in:
lib/datastax_rails/relation/batches.rb

Overview

Relation methods for operating on batches of records.

Instance Method Summary collapse

Instance Method Details

#find_each(options = {}) {|record| ... } ⇒ Object

Yields each record that was found by the find options. The find is performed by find_in_batches with a batch size of 1000 (or as specified by the :batch_size option).

Example:

Person.where(in_college: true).find_each do |person|
  person.party_all_night!
end

Note: This method is only intended to use for batch processing of large amounts of records that wouldn't fit in memory all at once. If you just need to loop over less than 1000 records, it's probably better just to use the regular find methods.

You can also pass the :start option to specify an offset to control the starting point.

Parameters:

  • options (Hash) (defaults to: {})

    finder options

Yields:

  • (record)

    a single DatastaxRails record



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# File 'lib/datastax_rails/relation/batches.rb', line 24

def find_each(options = {})
  find_in_batches(options) do |records|
    records.each { |record| yield record }
  end
end

#find_each_with_index(options = {}) ⇒ Object

Same as #find_each but yields the index as a second parameter.



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# File 'lib/datastax_rails/relation/batches.rb', line 31

def find_each_with_index(options = {})
  idx = 0
  find_in_batches(options) do |records|
    records.each do |record|
      yield record, idx
      idx += 1
    end
  end
end

#find_in_batches(options = {}) {|records| ... } ⇒ Object

Yields each batch of records that was found by the find options as an array. The size of each batch is set by the :batch_size option; the default is 1000.

You can control the starting point for the batch processing by supplying the :start option. This is especially useful if you want multiple workers dealing with the same processing queue. You can make worker 1 handle all the records between id 0 and 10,000 and worker 2 handle from 10,000 and beyond (by setting the :start option on that worker).

It's not possible to set the order. For Cassandra based batching, the order is set according to Cassandra's key placement strategy. For Solr based batching, the order is ascending order of the primary key. You can't set the limit either. That's used to control the batch sizes.

Example:

Person.where(in_college: true).find_in_batches do |group|
  sleep(50) # Make sure it doesn't get too crowded in there!
  group.each { |person| person.party_all_night! }
end

rubocop:disable Metrics/PerceivedComplexity

Parameters:

  • options (Hash) (defaults to: {})

    finder options

Yields:

  • (records)

    a batch of DatastaxRails records



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# File 'lib/datastax_rails/relation/batches.rb', line 67

def find_in_batches(options = {})
  relation = self

  unless @order_values.empty?
    DatastaxRails::Base.logger.warn('Scoped order and limit are ignored, ' \
                                    "it's forced to be batch order and batch size")
    relation = relation.clone
    relation.order_values.clear
  end
  if (finder_options = options.except(:start, :batch_size)).present?
    fail "You can't specify an order, it's forced to be #{@klass.primary_key}" if options[:order].present?
    fail "You can't specify a limit, it's forced to be the batch_size" if options[:limit].present?

    relation = apply_finder_options(finder_options)
  end

  start = options.delete(:start)
  batch_size = options.delete(:batch_size) || 1000

  relation = relation.limit(batch_size)
  relation = relation.order(@klass.primary_key) if relation.use_solr_value
  records = start ? relation.where(@klass.primary_key).greater_than(start).to_a : relation.to_a
  while records.size > 0
    records_size = records.size
    offset = records.last.__id
    yield records

    break if records_size < batch_size
    if offset
      offset = ::Cql::Uuid.new(offset.value + 1) if relation.use_solr_value
      records = relation.where(@klass.primary_key).greater_than(offset).to_a
    else
      fail 'Batch order not included in the custom select clause'
    end
  end
end