Class: ActiveRecordJsonStreamer::Streamer

Inherits:
Object
  • Object
show all
Defined in:
lib/active_record_json_streamer/streamer.rb

Constant Summary collapse

DEFAULT_BATCH_SIZE = 
1000
DEFAULT_LIMIT = 
50_000

Instance Attribute Summary collapse

Instance Method Summary collapse

Constructor Details

#initialize(relation, batch_size: DEFAULT_BATCH_SIZE, limit: DEFAULT_LIMIT, cursor_column: :created_at, primary_key: :id, order: :desc, &field_mapper) ⇒ Streamer

Returns a new instance of Streamer.



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# File 'lib/active_record_json_streamer/streamer.rb', line 12

def initialize(relation, batch_size: DEFAULT_BATCH_SIZE, limit: DEFAULT_LIMIT, cursor_column: :created_at, primary_key: :id, order: :desc, &field_mapper)
  @relation = relation
  @batch_size = batch_size
  @limit = limit
  @cursor_column = cursor_column
  @primary_key = primary_key
  @order = order.to_sym
  @field_mapper = field_mapper
end

Instance Attribute Details

#batch_size ⇒ Object (readonly)

Returns the value of attribute batch_size.



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# File 'lib/active_record_json_streamer/streamer.rb', line 10

def batch_size
  @batch_size
end

#cursor_column ⇒ Object (readonly)

Returns the value of attribute cursor_column.



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# File 'lib/active_record_json_streamer/streamer.rb', line 10

def cursor_column
  @cursor_column
end

#field_mapper ⇒ Object (readonly)

Returns the value of attribute field_mapper.



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# File 'lib/active_record_json_streamer/streamer.rb', line 10

def field_mapper
  @field_mapper
end

#limit ⇒ Object (readonly)

Returns the value of attribute limit.



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# File 'lib/active_record_json_streamer/streamer.rb', line 10

def limit
  @limit
end

#order ⇒ Object (readonly)

Returns the value of attribute order.



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# File 'lib/active_record_json_streamer/streamer.rb', line 10

def order
  @order
end

#primary_key ⇒ Object (readonly)

Returns the value of attribute primary_key.



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# File 'lib/active_record_json_streamer/streamer.rb', line 10

def primary_key
  @primary_key
end

#relation ⇒ Object (readonly)

Returns the value of attribute relation.



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# File 'lib/active_record_json_streamer/streamer.rb', line 10

def relation
  @relation
end

Instance Method Details

#enumerator ⇒ Object 



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# File 'lib/active_record_json_streamer/streamer.rb', line 22

def enumerator
  Enumerator.new do |yielder|
    yielder << "["
    first = true
    emitted = 0

    col = relation.connection.quote_column_name(cursor_column)
    pk = relation.connection.quote_column_name(primary_key)
    tbl = relation.connection.quote_table_name(relation.table_name)
    col_ref = "#{tbl}.#{col}"
    pk_ref = "#{tbl}.#{pk}"

    current_relation = relation.order(cursor_column => order, primary_key => order)

    loop do
      remaining = limit - emitted if limit
      break if remaining && remaining <= 0

      fetch_size = remaining ? [ batch_size, remaining ].min : batch_size
      batch = current_relation.limit(fetch_size).to_a
      break if batch.empty?

      batch.each do |record|
        yielder << "," unless first
        first = false
        data = field_mapper ? field_mapper.call(record) : record.as_json
        yielder << JSON.generate(data)
        emitted += 1
      end

      break if batch.size < fetch_size

      last = batch.last
      last_cursor = last.public_send(cursor_column)
      last_pk = last.public_send(primary_key)

      if order == :desc
        current_relation = relation.where(
          "(#{col_ref} < :ca) OR (#{col_ref} = :ca AND #{pk_ref} < :pk)",
          ca: last_cursor, pk: last_pk
        ).order(cursor_column => :desc, primary_key => :desc)
      else
        current_relation = relation.where(
          "(#{col_ref} > :ca) OR (#{col_ref} = :ca AND #{pk_ref} > :pk)",
          ca: last_cursor, pk: last_pk
        ).order(cursor_column => :asc, primary_key => :asc)
      end
    end

    yielder << "]"
  end
end