Regions as attributes

[JohnCEarls]

I like the idea of adding the region to the Model, but if you are already using region as an attribute (say because you use the table to track aws resources), you get an error (dynamodb not available in this region).

Not sure if this is solvable other than by A. 'region' is not an allowed attribute name or B. change the way the table regions are set/stored. In any case, this is an issue I figured you should be aware of.

Thanks for all your hard work.

[jlafon]

Hi John,

I agree that something should be done to avoid attribute name collisions, and I will leave this issue open for a while to let people comment on it before deciding how to fix it.

My goal is to keep the Model API simple and Pythonic. With that in mind, here are two possible solutions.

• A nested class for configuration. This is how Django and Django-Tastypie do it.

from pynamodb.models import Model
from pynamodb.attributes import UnicodeAttribute


class UserModel(Model):
    """A user model class"""
    class Meta:
        """A class for settings"""
        table_name = "users"
        region = "us-east-1"
    user_name = UnicodeAttribute(hash_key=True)

• Make setters for region (and other table level settings).

from pynamodb.models import Model
from pynamodb.attributes import UnicodeAttribute


class UserModel(Model):
    """A user model class"""
    table_name = "users"
    user_name = UnicodeAttribute(hash_key=True)

# This would have to be done before using UserModel
UserModel.set_region('us-east-1')

[adamchainz]

Hi,

I'm in favour of the Meta class, for similarity with the most popular ORM. But what about __ vars, like __region__ ? A lot of other ORM libraries use this pattern.

On this note, how is one supposed to use a PynamoDB Model with DynamoDBLocal? There's nowhere to set the endpoint url, which would be another Meta var...

[jlafon]

@adamchainz , using __region__ style variable names is not a bad idea. Although, I do prefer Meta because it cleanly encapsulates all of the configuration values.

There are two ways to set the endpoint URL for now:

from pynamodb.models import Model
from pynamodb.connection import TableConnection

class TestModel(Model):
    connection = TableConnection('table-name', host='http://localhost')

or

from pynamodb.models import Model
from pynamodb.connection import TableConnection

class TestModel(Model):
    # normal attributes here

TestModel.connection = TableConnection(TestModel.table_name, host='http://localhost')

If we change the API to include a Meta class, it could be like this:

from pynamodb.models import Model
from pynamodb.attributes import UnicodeAttribute


class UserModel(Model):
    """A user model class"""
    class Meta:
        """A class for settings"""
        table_name = "users"
        region = "us-east-1"
        host = 'http://localhost'
    user_name = UnicodeAttribute(hash_key=True)

[adamchainz]

👍 for Meta and encapsulating all the configuration in one place.

[jlafon]

I implemented the Meta class idea on a branch, you can see how it looks here