使用Ruby了解AWS DynamoDB中的属性

我似乎无法围绕DynamoDB的AWS Ruby SDK文档(或者更具体地说是DynamoDB数据模型的概念).

具体来说,我一直在阅读：http://docs.aws.amazon.com/AWSRubySDK/latest/frames.html#!AWS/DynamoDB.html

Note: I have read through the Data Model documentation as well and it’s still not sinking in; I’m hoping a proper example in Ruby with clear up my confusion

在下面的代码片段中,我创建了一个名为“my_books”的表,其中有一个名为“item_id”的primary_key,它是一个哈希键(不是哈希/范围组合)……

dyn = AWS::DynamoDB::Client::V20120810.new
# => #<AWS::DynamoDB::Client::V20120810>

dyn.create_table({
  :attribute_deFinitions => [
    { :attribute_name => "item_id",:attribute_type => "N" }
  ],:table_name => "my_books",:key_schema => [
    { :attribute_name => "item_id",:key_type => "HASH" },],:provisioned_throughput => {
    :read_capacity_units  => 10,:write_capacity_units => 10
  }
})
# => {:table_description=>{:attribute_deFinitions=>[{:attribute_name=>"item_id",:attribute_type=>"N"}],:table_name=>"my_books",:key_schema=>[{:attribute_name=>"item_id",:key_type=>"HASH"}],:table_status=>"ACTIVE",:creation_date_time=>2014-11-24 16:59:47 +0000,:provisioned_throughput=>{:number_of_decreases_today=>0,:read_capacity_units=>10,:write_capacity_units=>10},:table_size_bytes=>0,:item_count=>0}}

dyn.list_tables
# => {:table_names=>["my_books"]}

dyn.scan :table_name => "my_books"
# => {:member=>[],:count=>0,:scanned_count=>0}

然后我尝试使用新项目填充表格.我的理解是我应该为item_id(这是主键)指定数值,然后我可以为我正在添加到表中的新项目/记录/文档指定其他属性…

dyn.put_item(
  :table_name => "my_books",:item => {
    "item_id" => 1,"item_title" => "My Book Title","item_released" => false
  }
)

但是最后一个命令返回以下错误：

expected hash value for value at key item_id of option item

所以虽然我不太明白哈希会是什么,但我尝试这样做：

dyn.put_item(
  :table_name => "my_books",:item => {
    "item_id" => { "N" => 1 },"item_released" => false
  }
)

但现在这会返回以下错误…

expected string value for key N of value at key item_id of option item

我尝试了不同的变化,但似乎无法弄清楚它是如何工作的？

编辑/更新：根据Uri Agassi的建议 – 我将值从1更改为“1”.我不确定为什么必须引用它,因为我已经将类型定义为数字而不是字符串,但是好吧让我们接受这个并继续前进.

解决方法

我终于弄清楚了解DynamoDB数据模型和使用Ruby SDK所需的大部分内容.

下面是我的示例代码,希望能帮助其他人,我在这里有一个完整的例子：https://gist.github.com/Integralist/9f9f2215e001b15ac492#file-3-dynamodb-irb-session-rb

# https://github.com/BBC-News/alephant-harness can automate the below set-up when using SpurIoUs
# API Documentation http://docs.aws.amazon.com/amazondynamodb/latest/APIReference/API_Operations.html
# Ruby SDK API Documentation http://docs.aws.amazon.com/AWSRubySDK/latest/frames.html#!AWS/DynamoDB/Client/V20120810.html

require "aws-sdk"
require "dotenv"
require "spurIoUs/ruby/awssdk/helper"

SpurIoUs::Ruby::Awssdk::Helper.configure
# => <AWS::Core::Configuration>

Dotenv.load(
  File.join(
    File.dirname(__FILE__),"config","development","env.yaml"
  )
)
# => {"AWS_REGION"=>"eu-west-1","AWS_ACCESS_KEY_ID"=>"development_access","AWS_SECRET_ACCESS_KEY"=>"development_secret","DYNAMO_LU"=>"development_lookup","DYNAMO_SQ"=>"development_sequence","SQS_QUEUE"=>"development_queue","S3_BUCKET"=>"development_bucket"}

dyn = AWS::DynamoDB::Client.new :api_version => "2012-08-10"
dyn = AWS::DynamoDB::Client::V20120810.new
# => #<AWS::DynamoDB::Client::V20120810>

dyn.create_table({
  # This section requires us to define our primary key 
  # Which will be called "item_id" and it must be a numerical value
  :attribute_deFinitions => [
    { :attribute_name => "item_id",# The primary key will be a simple Hash key (not a Hash/Range which requires both key types to be provided)
  # The attributes defined above must be included in the :key_schema Array
  :key_schema => [
    { :attribute_name => "item_id",:key_type => "HASH" }
  ],:scanned_count=>0}

dyn.put_item(
  :table_name => "my_books",:item => {
    "item_id" => { "N" => "1" },# oddly this needs to be a String and not a strict Integer?
    "item_title" => { "S" => "My Book Title"},"item_released" => { "B" => "false" }
  }
)
# Note: if you use an "item_id" that already exists,then the item will be updated.
#       Unless you use the "expected" conditional feature

dyn.put_item(
  :table_name => "my_books","item_released" => { "B" => "false" }
  },# The :expected key specifies the conditions of our "put" operation.
  # If "item_id" isn't NULL (i.e. it exists) then our condition has Failed.
  # This means we only write the value when the key "item_id" hasn't been set.
  :expected => {
    "item_id" => { :comparison_operator => "NULL" }
  }
)
# AWS::DynamoDB::Errors::ConditionalCheckFailedException: The conditional check Failed

dyn.scan :table_name => "my_books"
# => {:member=>[{"item_id"=>{:n=>"1"},"item_title"=>{:s=>"My Book Title"},"item_released"=>{:b=>"false"}}],:count=>1,:scanned_count=>1}

dyn.query :table_name => "my_books",:consistent_read => true,:key_conditions => {
  "item_id" => {
    :comparison_operator => "EQ",:attribute_value_list => [{ "n" => "1" }]
  },"item_title" => {
    :comparison_operator => "EQ",:attribute_value_list => [{ "s" => "My Book Title" }]
  }
}
# => {:member=>[{"item_id"=>{:n=>"1"},:select => "SPECIFIC_ATTRIBUTES",:attributes_to_get => ["item_title"],:attribute_value_list => [{ "s" => "My Book Title" }]
  }
}
# => {:member=>[{"item_title"=>{:s=>"My Book Title"}}],:scanned_count=>1}

dyn.delete_item(
  :table_name => "my_books",:key => {
    "item_id" => { "n" => "1" }
  }
)
# => {:member=>[],:scanned_count=>0}

使用Ruby了解AWS DynamoDB中的属性

解决方法

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