NoMethodError-Ruby中AWS-SDK中User：Class的未定义方法'where'

Question

I am new to DynamoDB. I am using aws-sdk for ruby as ORM and I the following error when I try to execute User.where('name'=>'Joe') or User.all(:where => {:name => 'Joe'}) . Is this supported with aws-sdk or is there any other way to achieve this. My model looks like

class User < AWS::Record::HashModel
  string_attr :name
end

Thanks.

---

Error log:

Started GET "/users" for 127.0.0.1 at 2014-04-10 09:46:39 -0400 Processing by UsersController#index as HTML Completed 500 Internal Server Error in 3ms

NoMethodError (undefined method 'where' for User:Class): app/controllers/users_controller.rb:6:in index'

Answer 1

It seems HashModel is incomplete and where is only supported by AWS::Record::Model (SimpleDB).

The easiest way around I found is to fallback to the dynamo_db_table object.

For arbitrary parameters, using SCAN:

User.dynamo_db_table.items.where(name: 'Joe').select('id', 'surname').map(&:attributes)
User.dynamo_db_table.items.where(name: 'Joe', birthday: ('2014-04-10'..'2014-04-17')).select(*User.attributes.keys).map(&:attributes)
User.dynamo_db_table.items.where(name: 'Joe', birthday: ('2014-04-10'..'2014-04-17')).select(*User.attributes.keys, limit: 1).map(&:attributes)

For querying by hash_key, using QUERY:

User.dynamo_db_table.items.query(hash_value: 'Joe', select: User.attributes.keys).map(&:attributes)
User.dynamo_db_table.items.query(hash_value: 'Joe', select: User.attributes.keys, limit: 1).map(&:attributes)
User.dynamo_db_table.items.query(hash_value: 'Joe', select: User.attributes.keys, limit: 1, scan_index_forward: false).map(&:attributes)
User.dynamo_db_table.items.query(hash_value: 'Joe', range_value: '2014-04-10'..'2014-04-17', select: [:birthday], limit: 1, scan_index_forward: false).map(&:attributes)

More information here: http://docs.aws.amazon.com/AWSRubySDK/latest/AWS/DynamoDB/ItemCollection.html#query-instance_method

Answer 2

As per the error, User class doesn't have a class method named where present in it or in any of its ancestors.

Instead use User.all(:where => { :name => 'Joe' }) .

Refer to the Documentation of AWS::Record::HashModel Class