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# python3
# Copyright 2019 Google LLC
#
# Licensed under the Apache License, Version 2.0 (the "License");
# you may not use this file except in compliance with the License.
# You may obtain a copy of the License at
#
# https://www.apache.org/licenses/LICENSE-2.0
#
# Unless required by applicable law or agreed to in writing, software
# distributed under the License is distributed on an "AS IS" BASIS,
# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
# See the License for the specific language governing permissions and
# limitations under the License.
"""Transaction decorators."""
from typing import Callable, TypeVar
from spanner_orm import api
T = TypeVar('T')
def transactional_read(func: Callable[..., T]) -> Callable[..., T]:
"""Injects a read-only transaction as keyword argument to given function.
For example:
@transactional_read
def get_book(book_id, transaction=None):
return Book(book_id)
Client would then call this by skipping the 'transaction' argument:
book_reader.get_book(123)
To call a decorated function if you already have a transaction:
@transactional_read
def list_books(book_ids, transaction=None):
for book_id in book_ids:
get_book(book_id, transaction=transaction)
list_books method would call get_book method using same transaction
Args:
func: Callable which will be called with read-only transaction and original
arguments. Decorated `func` can also be passed an optional 'transaction'
kwarg to use a given transaction, instead of creating a new one.
Returns:
decorated function
"""
api_method_lambda = lambda: api.spanner_api().run_read_only
return _transactional(api_method_lambda, func)
def transactional_write(func: Callable[..., T]) -> Callable[..., T]:
"""Injects a write transaction object as first argument to given function.
For example:
@transactional_write
def save_book(book_id, transaction=None):
...
Client would then call this by skipping the 'transaction' argument:
book_reader.save_book(123)
To call a decorated function if you already have a transaction:
@transactional_write
def save_books(book_ids, transaction=None):
for book_id in book_ids:
save_book(book_id, transaction=transaction)
save_books method would call save_book method using same transaction
Args:
func: Callable which will be called with write transaction and original
arguments. Decorated `func` can also be passed an optional 'transaction'
kwarg to use a given transaction, instead of creating a new one.
Returns:
decorated function
"""
api_method_lambda = lambda: api.spanner_api().run_write
return _transactional(api_method_lambda, func)
def _transactional(spanner_api_method_lambda: Callable[[], Callable[..., T]],
func: Callable[..., T]) -> Callable[..., T]:
"""Returns decorated function."""
def wrapper(*args, **kwargs) -> T:
def spanner_wrapper(transaction) -> T:
# Spanner library calls given function with transaction as first argument.
# It will call 'spanner_wrapper', and we will move transaction from first
# argument to 'transaction' kwarg and call actual 'func'
return func(*args, transaction=transaction, **kwargs)
if 'transaction' in kwargs:
return func(*args, **kwargs)
spanner_api_method = spanner_api_method_lambda()
return spanner_api_method(spanner_wrapper)
return wrapper