Versioning

​

What are feature versions

Feature versions allow you to manage a feature as its definition changes over time. You can reference versions of a feature when querying, in resolvers, in migrations, and anywhere you use features!

The ability to maintain multiple versions of a feature is especially useful as your use cases evolve and the definition of a feature changes. This might be because your old feature had a bug, or maybe you want to improve the feature to be even more useful.

Changing the definition of a feature can have unexpected side effects, especially when there might be many consumers of a feature, some of which you may be unaware of. Feature versions allow you to update the feature definition without worrying that you might affect these consumers unknowingly.

Try it out yourself with this tutorial.

​

Definition

To define a versioned feature, supply the version keyword argument to the feature function. This allows you to continue adding versions without affecting past versions.

@features
class Trial:
    id: int
    code: str = feature(version=2)

​

Querying

You can refer to a specific version of a feature using the @ operator. You can query versioned features from any client, including the CLI, Python, etc.

$ chalk query --in trial.id=1 --out trial.code@2

​

Default versions

When you define a versioned feature, that feature always has a default version. When you reference a versioned feature without the @ operator, you reference the default version. The default version can be controlled by adding the default_version keyword argument to the feature function. If no default_version is provided, the default version is 1. It is best practice to leave the default as 1 until all consumers have been updated to use a newer version.

@features
class Trial:
    id: int
    code: str = feature(version=2, default_version=2)

​

Resolvers

Resolvers also reference versioned features with @. Resolvers can take versions of a feature as input, return them as output, or both. Chalk will always generate the right version of a feature when chaining resolvers that require versioned features.

​

Requesting versioned features

@online
def fn(code: Trial.code) -> Trial.failed:
    # Default version is 1.
    return code in {'failed', 'err'}

@online
def fn2(code: Trial.code@2) -> Trial.failed:
    # Version 2 is specifically requested.
    return code in {'FAILED', 'ERR'}

​

Producing versioned features

@online
def fn(d: Trial.raw_data) -> Trial.code @ 1:
    return d['code']

@online
def fn2(d: Trial.raw_data) -> Trial.code @ 2:
    return d['data']['code']

​

Limitations

Only scalar features can be versioned. Other kinds of features cannot be versioned. These include:

• has_one and has_many
• FeatureTime
• Windowed
• Primary