使用Ruby了解AWS DynamoDB中的属性

Question

我似乎无法将自己的头围绕DynamoDB的AWS Ruby SDK文档（或更具体地说是DynamoDB数据模型的概念）。

具体来说，我一直在读：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”表，该表有一个名为“ITEM_ID” primary_key，这是一个哈希键（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} 

然后我尝试用新项目填充表格。我的理解是，我应该为item_id指定数值（这是主键），然后我可以指定新项目/记录/文件我加入到表中的其他属性...

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

但是，最后的命令返回以下错误：

expected hash value for value at key item_id of option item 

所以，虽然我不太明白什么是哈希将作出的，我试着这样做：

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

但现在返回以下错误...

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

我试过不同的变化，但似乎无法弄清楚这是如何工作的？

---

EDIT/UPDATE：通过开放的阿加西所建议 - I值改变从1到"1"。我不太确定为什么这必须引用，因为我已经将类型定义为数字而不是字符串，但好吧，让我们接受它并继续。

Answer 1

我终于明白了解我需要了解DynamoDB的数据模型以及使用Ruby SDK的大部分内容。

下面是我的示例代码，希望能帮助别人，我已经有了一个完全充实的例子在这里：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", :attribute_type => "N" } 
    ], 
    :table_name => "my_books", 
    # 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" } 
    ], 
    :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} 

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 => { 
    "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" } 
    }, 
    # 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"}, "item_title"=>{:s=>"My Book Title"}, "item_released"=>{:b=>"false"}}], :count=>1, :scanned_count=>1} 

dyn.query :table_name => "my_books", 
    :consistent_read => true, 
    :select => "SPECIFIC_ATTRIBUTES", 
    :attributes_to_get => ["item_title"], 
    :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_title"=>{:s=>"My Book Title"}}], :count=>1, :scanned_count=>1} 

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