Class: Google::Cloud::Datastore::ReadOnlyTransaction

Inherits:
Object
  • Object
show all
Defined in:
lib/google/cloud/datastore/read_only_transaction.rb

Overview

ReadOnlyTransaction

Represents a read-only Datastore transaction that only allows reads.

A read-only transaction cannot modify entities; in return they do not contend with other read-write or read-only transactions. Using a read-only transaction for transactions that only read data will potentially improve throughput.

See Dataset#transaction

Examples:

require "google/cloud/datastore"

datastore = Google::Cloud::Datastore.new

task_list_key = datastore.key "TaskList", "default"
query = datastore.query("Task").
  ancestor(task_list_key)

tasks = nil

datastore.read_only_transaction do |tx|
  task_list = tx.find task_list_key
  if task_list
    tasks = tx.run query
  end
end

See Also:

Instance Attribute Summary collapse

Instance Method Summary collapse

Instance Attribute Details

#id ⇒ Object (readonly)

Returns the value of attribute id



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# File 'lib/google/cloud/datastore/read_only_transaction.rb', line 56

def id
  @id
end

Instance Method Details

#commit ⇒ Object

Commits the transaction.

Examples:

require "google/cloud/datastore"

datastore = Google::Cloud::Datastore.new

task_list_key = datastore.key "TaskList", "default"
query = datastore.query("Task").
  ancestor(task_list_key)

tx = datastore.transaction
task_list = tx.find task_list_key
if task_list
  tasks = tx.run query
end
tx.commit


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# File 'lib/google/cloud/datastore/read_only_transaction.rb', line 192

def commit
  if @id.nil?
    raise TransactionError, "Cannot commit when not in a transaction."
  end

  ensure_service!

  service.commit [], transaction: @id
  true
end

#find(key_or_kind, id_or_name = nil) ⇒ Google::Cloud::Datastore::Entity? Also known as: get

Retrieve an entity by providing key information. The lookup is run within the transaction.

Examples:

require "google/cloud/datastore"

datastore = Google::Cloud::Datastore.new

task_list_key = datastore.key "TaskList", "default"

datastore.read_only_transaction do |tx|
  task_list = tx.find task_list_key
end

Parameters:

  • key_or_kind (Key, String) —

    A Key object or kind string value.

Returns:



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# File 'lib/google/cloud/datastore/read_only_transaction.rb', line 91

def find key_or_kind, id_or_name = nil
  key = key_or_kind
  unless key.is_a? Google::Cloud::Datastore::Key
    key = Key.new key_or_kind, id_or_name
  end
  find_all(key).first
end

#find_all(*keys) ⇒ Google::Cloud::Datastore::Dataset::LookupResults Also known as: lookup

Retrieve the entities for the provided keys. The lookup is run within the transaction.

Examples:

require "google/cloud/datastore"

datastore = Google::Cloud::Datastore.new

task_key1 = datastore.key "Task", 123456
task_key2 = datastore.key "Task", 987654

datastore.read_only_transaction do |tx|
  tasks = tx.find_all task_key1, task_key2
end

Parameters:

  • keys (Key) —

    One or more Key objects to find records for.

Returns:



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# File 'lib/google/cloud/datastore/read_only_transaction.rb', line 120

def find_all *keys
  ensure_service!
  lookup_res = service.lookup(*Array(keys).flatten.map(&:to_grpc),
                              transaction: @id)
  Dataset::LookupResults.from_grpc lookup_res, service, nil, @id
end

#reset! ⇒ Object

Reset the transaction. #start must be called afterwards.



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# File 'lib/google/cloud/datastore/read_only_transaction.rb', line 235

def reset!
  @id = nil
end

#rollback ⇒ Object

Rolls back the transaction.

Examples:

require "google/cloud/datastore"

datastore = Google::Cloud::Datastore.new

task_list_key = datastore.key "TaskList", "default"
query = datastore.query("Task").
  ancestor(task_list_key)

tx = datastore.transaction
task_list = tx.find task_list_key
if task_list
  tasks = tx.run query
end
tx.rollback


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# File 'lib/google/cloud/datastore/read_only_transaction.rb', line 222

def rollback
  if @id.nil?
    raise TransactionError, "Cannot rollback when not in a transaction."
  end

  ensure_service!
  service.rollback @id
  true
end

#run(query, namespace: nil) ⇒ Google::Cloud::Datastore::Dataset::QueryResults Also known as: run_query

Retrieve entities specified by a Query. The query is run within the transaction.

Examples:

require "google/cloud/datastore"

datastore = Google::Cloud::Datastore.new

query = datastore.query("Task").
  where("done", "=", false)
datastore.read_only_transaction do |tx|
  tasks = tx.run query
end

Parameters:

  • query (Query) —

    The Query object with the search criteria.

  • namespace (String) —

    The namespace the query is to run within.

Returns:



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# File 'lib/google/cloud/datastore/read_only_transaction.rb', line 148

def run query, namespace: nil
  ensure_service!
  unless query.is_a?(Query) || query.is_a?(GqlQuery)
    raise ArgumentError, "Cannot run a #{query.class} object."
  end
  query_res = service.run_query query.to_grpc, namespace,
                                transaction: @id
  Dataset::QueryResults.from_grpc query_res, service, namespace,
                                  query.to_grpc.dup
end

#start ⇒ Object Also known as: begin_transaction

Begins a transaction. This method is run when a new ReadOnlyTransaction is created.

Raises:



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# File 'lib/google/cloud/datastore/read_only_transaction.rb', line 164

def start
  raise TransactionError, "Transaction already opened." unless @id.nil?

  ensure_service!
  tx_res = service.begin_transaction read_only: true
  @id = tx_res.transaction
end