NANVEL

DynamoDB in examples, Example 1.3: DynamoDB local and testing

May be useful for:

  • development without steady internet connection
  • testing
  • reduce ddb usage costs

See DynamoDB local documentation.

I use Makefile to run DynamoDB locally:

dynamodb:
    java -Djava.library.path=./bin/DynamoDBLocal_lib -jar ./bin/DynamoDBLocal.jar -port 8010 -inMemory # -dbPath ./bin/db.bin

And usually I run it with inMemory key, that allows to have a clean database after restart.

You can download DynamoDB local binaries from DynamoDB local documentation page. I place binaries in ./bin folder of the project:

- project
    - bin
        - DynamoDBLocal.jar
        - DynamoDBLocal_lib
    - Makefile

To use DynamoDB local instead of amazon service, we need to set endpoint url to our DynamoDB local server url:

http://localhost:8010

Let's write a functional test for our previous example to see how it works:

import unittest
import uuid

from example_1 import DDBUserWallet
from unittest import mock


DDB_LOCAL_URL = 'http://localhost:8010'


class DDBUserWalletTestCase(unittest.TestCase):

    @mock.patch('example_1.DDBUserWallet._get_endpoint_url')
    def test_update_and_get(self, _get_endpoint_url_mock):
        _get_endpoint_url_mock.return_value = DDB_LOCAL_URL
        user_wallet = DDBUserWallet()
        user_wallet.create_table()
        user_id = uuid.uuid4()
        for balance in [100, 123]:
            user_wallet.update(user_id=user_id, balance=balance)
            self.assertEqual(user_wallet.get(user_id=user_id)['balance'], balance)


if __name__ == '__main__':
    unittest.main()
    # (.env)nanvel-air:example_1_3 nanvel$ python example_1_3.py
    # .
    # ----------------------------------------------------------------------
    # Ran 1 test in 0.323s
    #
    # OK

You also may use decorator like this instead @mock.patch:

import functools

from mock import patch


DDB_LOCAL_URL = 'http://localhost:8010'


def with_ddb_local(method):

    @functools.wraps(method)
    def wrapper(self, *args, **kwargs):
        return patch(
            'example_1.DDBUserWallet._get_endpoint_url',
            new=lambda x: DDB_LOCAL_URL)(
                method)(self, *args, **kwargs)
    return wrapper

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