Understanding Attributes in AWS DynamoDB with Ruby

Question

I seem to be unable to plunge my head into the AWS Ruby SDK documentation for DynamoDB (or, more specifically, the DynamoDB data model concept).

In particular, I read: http://docs.aws.amazon.com/AWSRubySDK/latest/frames.html#!AWS/DynamoDB.html

Note. I also read the data model documentation and still don't dive; I am hoping for the right example in Ruby by clearing my confusion.

In the following code snippet, I create a table called "my_books" that has a primary_key named "item_id" and this is a hash key (not a Hash / Range combination) ...

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} 

Then I will try to populate the table with a new element. I understand that I have to specify a numeric value for item_id (this is the primary key), and then I could specify other attributes for the new item / record / document that I add to the table ...

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

But this last command returns the following error:

 expected hash value for value at key item_id of option item 

So, although I do not quite understand what the hash is made of, I try to do this:

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

But now it returns the following error ...

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

I tried different options but can't figure out how this works?

---

EDIT / UPDATE : as suggested by Uri Agassi - I changed the value from 1 to "1" . I'm not sure why this should be indicated, as I defined the type as a number, not a string, but OK, just to accept it and move on.

Answer 1

I finally realized that I needed to understand the DynamoDB data model and use the Ruby SDK.

Below is my sample code, which I hope will help someone else, and here I have a complete example: 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 (ie 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}