Class: Dynamoid::TransactionRead

Inherits:
Object
  • Object
show all
Defined in:
lib/dynamoid/transaction_read.rb,
lib/dynamoid/transaction_read/find.rb

Overview

The class TransactionRead provides means to perform multiple reading operations in transaction, that is atomically, so that either all of them succeed, or all of them fail.

The reading methods are supposed to be as close as possible to their non-transactional counterparts:

user_id = params[:user_id]
payment = params[:payment_id]

models = Dynamoid::TransactionRead.execute do |t|
  t.find User, user_id
  t.find Payment, payment_id
end

The only difference is that the methods are called on a transaction instance and a model or a model class should be specified. So User.find becomes t.find(user_id) and Payment.find(payment_id) becomes t.find Payment, payment_id.

A transaction can be used without a block. This way a transaction instance should be instantiated and committed manually with #commit method:

t = Dynamoid::TransactionRead.new

t.find user_id
t.find payment_id

models = t.commit

### DynamoDB’s transactions

The main difference between DynamoDB transactions and a common interface is that DynamoDB’s transactions are executed in batch. So in Dynamoid no data actually loaded when some transactional method (e.g+ ‘#find+) is called. All the changes are loaded at the end.

A TransactGetItems DynamoDB operation is used (see [documentation](docs.aws.amazon.com/amazondynamodb/latest/APIReference/API_TransactGetItems.html) for details).

Defined Under Namespace

Classes: Find

Class Method Summary collapse

Instance Method Summary collapse

Constructor Details

#initialize ⇒ TransactionRead

Returns a new instance of TransactionRead.



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# File 'lib/dynamoid/transaction_read.rb', line 57

def initialize
  @actions = []
end

Class Method Details

.execute ⇒ Object 



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# File 'lib/dynamoid/transaction_read.rb', line 48

def self.execute
  transaction = new

  begin
    yield transaction
    transaction.commit
  end
end

Instance Method Details

#commit ⇒ Object

Load all the models.

transaction = Dynamoid::TransactionRead.new
# ...
transaction.commit



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# File 'lib/dynamoid/transaction_read.rb', line 66

def commit
  return [] if @actions.empty?

  # some actions may produce multiple requests
  action_request_groups = @actions.map(&:action_request).map do |action_request|
    action_request.is_a?(Array) ? action_request : [action_request]
  end
  action_requests = action_request_groups.flatten(1)

  return [] if action_requests.empty?

  response = Dynamoid.adapter.transact_read_items(action_requests)

  responses = response.responses.dup
  @actions.zip(action_request_groups).map do |action, action_requests|
    action_responses = responses.shift(action_requests.size)
    action.process_responses(action_responses)
  end.flatten
end

#find(model_class, *ids, **options) ⇒ nil

Find one or many objects, specified by one id or an array of ids.

By default it raises RecordNotFound exception if at least one model isn’t found. This behavior can be changed with raise_error option. If specified raise_error: false option then find will not raise the exception.

When a document schema includes range key it should always be specified in find method call. In case it’s missing MissingRangeKey exception will be raised.

Please note that there are the following differences between transactional and non-transactional find:

  • transactional find preserves order of models in result when given multiple ids

  • transactional find doesn’t return results immediately, a single collection with results of all the find calls is returned instead

  • :consistent_read option isn’t supported

  • transactional find is subject to limitations of the [TransactGetItems](docs.aws.amazon.com/amazondynamodb/latest/APIReference/API_TransactGetItems.html) DynamoDB operation, e.g. the whole read transaction can load only up to 100 models.

Examples:

Find by partition key

Dynamoid::TransactionRead.execute do |t|
  t.find Document, 101
end

Find by partition key and sort key

Dynamoid::TransactionRead.execute do |t|
  t.find Document, 101, range_key: 'archived'
end

Find several documents by partition key

Dynamoid::TransactionRead.execute do |t|
  t.find Document, 101, 102, 103
  t.find Document, [101, 102, 103]
end

Find several documents by partition key and sort key

Dynamoid::TransactionRead.execute do |t|
  t.find Document, [[101, 'archived'], [102, 'new'], [103, 'deleted']]
end

Parameters:

  • ids (Object|Array) —

    a single primary key or an array of primary keys

  • options (Hash) —

    optional parameters of the operation

Options Hash (**options):

  • :range_key (Object) —

    sort key of a model; required when a single partition key is given and a sort key is declared for a model

  • :raise_error (true|false) —

    whether to raise a RecordNotFound exception; specify explicitly raise_error: false to suppress the exception; default is true

Returns:

  • (nil) 


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# File 'lib/dynamoid/transaction_read.rb', line 133

def find(model_class, *ids, **options)
  action = Dynamoid::TransactionRead::Find.new(model_class, *ids, **options)
  register_action action
end