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# Copyright 2011-2013 Amazon.com, Inc. or its affiliates. All Rights Reserved.
#
# Licensed under the Apache License, Version 2.0 (the "License"). You
# may not use this file except in compliance with the License. A copy of
# the License is located at
#
# http://aws.amazon.com/apache2.0/
#
# or in the "license" file accompanying this file. This file is
# distributed on an "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF
# ANY KIND, either express or implied. See the License for the specific
# language governing permissions and limitations under the License.
module AWS
class DynamoDB
# A utility class for configuring a list of tables, attributes and
# items to request information for.
#
# @see DynamoDB#batch_get
# @see Table#batch_get
#
class BatchGet
include Keys
include Enumerable
include Core::Model
def initialize options = {}
super(options)
@request_items = {}
end
# Add a list of items to fetch in this batch.
#
# @param [Table,String] table 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), ...])
#
# @param [Hash] options
#
# @option options [Boolean] :consistent_read (false) When `true`, items
# are read from this table with consistent reads. When `false`, reads
# are eventually consistent.
#
# @return [nil]
#
def table table, attributes, items, options = {}
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
@request_items[table].merge!(options)
nil
end
# 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.
#
def items attributes, *items
[items].flatten.each do |item|
self.table(item.table, attributes, [item])
end
end
# @return [nil]
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
# 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.
def each_attributes
each do |table_name, attributes|
yield(attributes)
end
end
protected
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
end
end
end
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