dynamodel.py

import inspect
import json
import os
import boto3
import decimal

from core import interface
from core.interface import Model, Throughput, Key


def model_constructor(obj):
    # CONSIDER CASE IN WHICH TABLE ALREADY EXISTS AND ONLY HAS TO BE UPDATED!!!!

    # For some of the attributes defined in the table we might need additional checks, which might
    # justify moving the logic into a TableModel class to build it.
    table_attributes = ['TableName', 'KeySchema', 'AttributeDefinitions', 'ProvisionedThroughput',
                        'GlobalSecondaryIndexes',
                        'LocalSecondaryIndexes', 'StreamSpecification']
    table_model = {
        'TableName': None,
        'KeySchema': [],
        'AttributeDefinitions': [],
        'ProvisionedThroughput': None
    }

    model = obj.__call__()  # obj() also works, but I think this syntax is more explicit.
    attributes = model.get_attributes()
    table_name = attributes.get('table_name', model.__class__)
    provisioned_throughput = attributes.get('provisioned_throughput', Throughput(read=5, write=5))
    keys = [(key, value) for key, value in attributes.items() if isinstance(value, Key)]
    # Keys must be listed in order when creating a table in DynamoDB. Hash key must come first,
    # and RANGE key second, if any. The sorting method used here is not very good, since it
    # relies on alphabetical order on the one hand, and on the other hand the key referrencing
    # method is very specific to the API implemented in this framework, which makes it prone to
    # code breaks with small changes. Improve this later.
    keys = sorted(keys, key=lambda key: key[1].get_values().KeySchema['KeyType'])

    table_model['TableName'] = table_name
    table_model['ProvisionedThroughput'] = provisioned_throughput.get_values()

    for key, value in keys:
        values = value.get_values()

        schema = values.KeySchema
        definitions = values.AttributeDefinitions

        attr_name = schema.get('AttrbuteName', key)

        schema['AttributeName'] = attr_name
        definitions['AttributeName'] = attr_name

        table_model['KeySchema'].append(schema)
        table_model['AttributeDefinitions'].append(definitions)

    return table_model


def migrate():
    # The database connection must be built from the settings.py file, not like this
    dynamodb = boto3.resource('dynamodb', region_name='us-west-2',
                              endpoint_url='http://localhost:8000')
    with open(os.path.join('migration_logs', 'migration.json')) as json_file:
        tables = json.load(json_file, parse_float=decimal.Decimal)
        for table in tables:
            response = dynamodb.create_table(**table)
            print(response)


def makemigrations():
    class_models = []
    table_models = []
    for name, obj in inspect.getmembers(interface, inspect.isclass):
        # HORROR!!!!!!!!!!! CHANGE THIS ASAP!!!!!!!!!!
        if 'models_package' not in repr(obj):
            class_models.append(obj)

    for obj in class_models:
        table_model = model_constructor(obj)
        table_models.append(table_model)

    with open(os.path.join('migration_logs', 'migration.json'), 'w') as json_file:
        json.dump(table_models, json_file, indent=4)
    print('Migration file completed')


# log()


if __name__ == '__main__':
    import sys

    valid_commands = {'migrate': migrate, 'makemigrations': makemigrations}

    try:
        command = sys.argv[1]
    except IndexError:
        print("Please provide a command")
        sys.exit()

    try:
        valid_commands[command].__call__()
    except KeyError as e:
        print('Please provide a valid command, ', e)