class AWS::DynamoDB::BatchGet

A utility class for configuring a list of tables, attributes and items to request information for.

@see AWS::DynamoDB#batch_get @see AWS::DynamoDB::Table#batch_get

Public Class Methods

new(options = {}) click to toggle source

# File lib/aws/dynamo_db/batch_get.rb, line 29
def initialize options = {}
  super(options)
  @request_items = {}
end

Public Instance Methods

each() { |table_name, attributes| ... } click to toggle source

@return [nil]

# File lib/aws/dynamo_db/batch_get.rb, line 135
def each &block

  options = { :request_items => @request_items }

  begin

    response = client.batch_get_item(options)

    response.data['Responses'].each_pair do |table_name,details|
      details['Items'].each do |hash_data|
        attributes = values_from_response_hash(hash_data)
        yield(table_name, attributes)
      end
    end

    options[:request_items] = convert_unprocessed_keys(response)

  end while options[:request_items]

  nil

end

each_attributes() { |attributes| ... } click to toggle source

Yields only attribute hashes. This removes the outer hash that normally provides the :table_name and :attributes keys. This is useful when your batch get requested items from a single table.

# File lib/aws/dynamo_db/batch_get.rb, line 161
def each_attributes
  each do |table_name, attributes|
    yield(attributes)
  end
end

items(attributes, *items) click to toggle source

Specify a list of {Item} objects to batch fetch attributes for. The table name is retrieved from the items objects, this means the items do not need to belong to the same table.

@param [Symbol, String, Array<String>] attributes The list of attributes

to fetch.  If you want to load *ALL* attributes for the named items,
then pass the symbol +:all+.

  # get all attributes
  batch_get.table('mytable', :all, items)

  # get one attribute for each item
  batch_get.table('mytable', ['name'], items)

  # get a list of attributes for each item
  batch_get.table('mytable', ['name', 'size'], items)

@param [Item] items One or more {Item} objects to fetch attributes

for.  These items may come from any number of different tables.

# File lib/aws/dynamo_db/batch_get.rb, line 128
def items attributes, *items
  [items].flatten.each do |item|
    self.table(item.table, attributes, [item])
  end
end

table(table, attributes, items) click to toggle source

Add a list of items to fetch in this batch.

@param [String] table_name The name of the table to fetch attributes

from.

@param [Symbol, String, Array<String>] attributes The list of attributes

to fetch.  If you want to load *ALL* attributes for the named items,
then pass the symbol +:all+.

  # get all attributes
  batch_get.table('mytable', :all, items)

  # get one attribute for each item
  batch_get.table('mytable', ['name'], items)

  # get a list of attributes for each item
  batch_get.table('mytable', ['name', 'size'], items)

@param [Array<Item,Array>] items One or more items to fetch attributes

for.  Each attribute should be one of the following:

* an {Item} object
* a hash key value
* a hash key value and a range key value

You must provide both the hash key and range key values if the table
schema has both.

  batch_get.table('mytable', :all, [%w(hk1 rk1), %w(hk1 rk2), ...])

@return [nil]

# File lib/aws/dynamo_db/batch_get.rb, line 66
def table table, attributes, items

  table = table.is_a?(Table) ? table.name : table.to_s

  attributes = attributes == :all ? nil : [attributes].flatten

  keys = items.collect do |item|
    case item
    when Item then item_key_hash(item)
    when Array 
      {
        :hash_key_element => format_attribute_value(item[0]),
        :range_key_element => format_attribute_value(item[1]),
      }
    else
      { :hash_key_element => format_attribute_value(item) }
    end
  end

  ## ensure we don't receive 2 different lists of attributes for
  ## the same table

  if 
    @request_items.has_key?(table) and 
    @request_items[table][:attributes_to_get] != attributes
  then
    msg = "When batch getting attributes, you may only provide " +
      "1 list of attributes per table, but the `#{table}` table " +
      "has received reqeusts for 2 different sets of attributes"
    raise ArgumentError, msg
  end

  ## merge attributes and items with the request items

  @request_items[table] ||= { :keys => [] } 
  @request_items[table][:attributes_to_get] = attributes if attributes
  @request_items[table][:keys] += keys

  nil

end

Protected Instance Methods

convert_unprocessed_keys(response) click to toggle source

# File lib/aws/dynamo_db/batch_get.rb, line 168
def convert_unprocessed_keys response
  
  return nil if response.data['UnprocessedKeys'].empty?
  
  # convert the json response keys into symbolized keys
  str2sym = lambda do |key_desc|
    type, value = key_desc.to_a.flatten
    case type
    when "S" then { :s => value }
    when "N" then { :n => value }
    else 
      raise "unhandled key type: #{type}"
    end
  end

  request_items = {}
  response.data['UnprocessedKeys'].each_pair do |table,keys|

    request_items[table] = {}

    request_items[table][:attributes_to_get] = keys['AttributesToGet'] if
      keys['AttributesToGet']

    request_items[table][:keys] = keys['Keys'].collect do |desc|
      key = {}
      key[:hash_key_element] = str2sym.call(desc['HashKeyElement'])
      key[:range_key_element] = str2sym.call(desc['RangeKeyElement']) if
        desc['RangeKeyElement']
      key
    end

  end
  request_items

end