Support conditions= for save and put operations

[ricky-sb]

Class looks like:

from dynamorm import DynaModel
from marshmallow.fields import String

class Device(DynaModel):
    class Table:
        name = 'Device'
        hash_key = 'device_id'
        read = 1
        write = 1

    class Schema:
        device_id = String(required=True)

When I do:

device = Device(device_id='test')
device.save(conditions=dict(device_id__ne='BAD_DEVICE_ID'))

I get this traceback.

Traceback (most recent call last):
  File "~/example.py", line 71, in <module>
    device.save(conditions=dict(device_id__ne='BAD_DEVICE_ID'))
  File "~/venv/lib/site-packages/dynamorm/model.py", line 470, in save
    resp = self.Table.put(as_dict, **kwargs)
  File "~/venv/lib/site-packages/dynamorm/table.py", line 566, in put
    return self.table.put_item(Item=remove_nones(item), **kwargs)
  File "~/venv/lib/site-packages/boto3/resources/factory.py", line 520, in do_action
    response = action(self, *args, **kwargs)
  File "~/venv/lib/site-packages/boto3/resources/action.py", line 83, in __call__
    response = getattr(parent.meta.client, operation_name)(**params)
  File "~/venv/lib/site-packages/botocore/client.py", line 357, in _api_call
    return self._make_api_call(operation_name, kwargs)
  File "~/venv/lib/site-packages/botocore/client.py", line 634, in _make_api_call
    api_params, operation_model, context=request_context)
  File "~/venv/lib/site-packages/botocore/client.py", line 682, in _convert_to_request_dict
    api_params, operation_model)
  File "~/venv/lib/site-packages/botocore/validate.py", line 297, in serialize_to_request
    raise ParamValidationError(report=report.generate_report())
botocore.exceptions.ParamValidationError: Parameter validation failed:
Unknown parameter in input: "conditions", must be one of: TableName, Item, Expected, ReturnValues, ReturnConsumedCapacity, ReturnItemCollectionMetrics, ConditionalOperator, ConditionExpression, ExpressionAttributeNames, ExpressionAttributeValues

It does however, work with update:

device = Device(device_id='test')
device.save(conditions=dict(device_id__ne='BAD_DEVICE_ID'))

[ricky-sb]

After playing with this library some more, I realize the appropriate method to use would be put, however, put doesn't support the conditions kwarg. We have to manually construct a ConditionExpression which gets passed to boto3.