Extensions

extension The core metadata schema in ADL covers what every data solution has — connections, objects, columns, mappings, classifications, relationships. But every project has its own quirks. You might need to record a deployment flag, a downstream owner, a refresh cadence, or a feature toggle for a template. Extensions are how you attach that custom information without forking the schema.

What is an extension?

An extension is a key-value pair attached to a metadata entity. The key is a name you choose; the value is a string. Extensions can be added to:

• Data Objects — for example, a SchemaName value used by templates, or an OwningTeam tag for documentation.
• Data Items — for example, a MaskingRule for a sensitive column, or a SourceColumnName mapping aid.

The schema doesn’t constrain what extensions you create or how many — that’s deliberate. Extensions are the open-ended slot in the metadata model.

Why extensions matter

The point of extensions is to keep your project’s specific needs in the metadata, where templates can act on them.

• Templates can read them. A Handlebars template can call extension_lookupextension to fetch a value and use it in generated output — different schema names per environment, different deployment flags per table, custom comment text, anything.
• Templates can branch on them. Use extension_exists to generate one thing when an extension is present and something else when it isn’t.
• They’re plain JSON. Extensions are stored alongside the rest of the metadata in your project files, so they’re versioned, diffable, and editable outside the app if you need to.

Common patterns

• Environment-specific values — EnvironmentName, DeploymentSchema per object.
• Operational metadata — OwningTeam, OnCallChannel, RefreshFrequency.
• Template hints — Flags that templates check to enable/disable optional output sections (for example, a HasControlFramework flag — see has-control-framework).
• Source-mapping aids — OriginalColumnName, SourceQuery notes.

Working with extensions in ADL

You manage extensions inline on the Data Objects screen. Each Data Object and Data Item has an extensions panel where you can:

• Add a new extension with a key and value.
• Edit or remove existing extensions.
• See all extensions on the entity at a glance.

For more complex cases, the full extension editor lets you manage many extensions at once.

What’s next?

• Handlebars Helpers — extension_exists and extension_lookupextension are the two helpers most commonly used with extensions.
• Data Objects — Where you attach extensions to objects and columns.
• Templates & Code Generation — How templates consume metadata, including extensions.