Adding Dagster definitions to a dg project

info

dg and Dagster Components are under active development. You may encounter feature gaps, and the APIs may change. To report issues or give feedback, please join the #dg-components channel in the Dagster Community Slack.

dg can be used to scaffold Dagster definitions such as assets, schedules, and sensors. When you use a project that has been scaffolded using dg, any new definitions added underneath the defs directory will be automatically loaded into the top-level Definitions object. This allows you to easily add new definitions to your project without needing to explicitly import these definitions to your top-level definitions file.

This guide will walk through how to use dg to scaffold a new asset.

Scaffold an asset

You can use the dg scaffold command to scaffold a new asset underneath the defs folder. In this example, we scaffold an asset named my_asset.py and write it to the defs/assets directory:

dg scaffold defs dagster.asset assets/my_asset.py

Creating a component at /.../my-project/src/my_project/defs/assets/my_asset.py.

Once this is done, we can see that a new file has been added to this location, and view its contents:

tree

.
├── pyproject.toml
├── src
│   └── my_project
│       ├── __init__.py
│       ├── components
│       │   └── __init__.py
│       ├── definitions.py
│       └── defs
│           ├── __init__.py
│           └── assets
│               └── my_asset.py
├── tests
│   └── __init__.py
└── uv.lock

7 directories, 8 files

cat src/my_project/defs/assets/my_asset.py

import dagster as dg


@dg.asset
def my_asset(context: dg.AssetExecutionContext) -> dg.MaterializeResult: ...

Write a definition

As seen in the above example, the scaffolded asset contains a basic commented-out definition. We can replace this definition with whatever asset code we're interested in:

import dagster as dg


@dg.asset(group_name="my_group")
def my_asset(context: dg.AssetExecutionContext) -> None:
    """Asset that greets you."""
    context.log.info("hi!")

Check your work

Finally, we can run dg list defs to confirm that the new asset now appears in the list of definitions:

dg list defs

┏━━━━━━━━━┳━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━┓
┃ Section ┃ Definitions                                                     ┃
┡━━━━━━━━━╇━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━┩
│ Assets  │ ┏━━━━━━━━━━┳━━━━━━━━━━┳━━━━━━┳━━━━━━━┳━━━━━━━━━━━━━━━━━━━━━━━━┓ │
│         │ ┃ Key      ┃ Group    ┃ Deps ┃ Kinds ┃ Description            ┃ │
│         │ ┡━━━━━━━━━━╇━━━━━━━━━━╇━━━━━━╇━━━━━━━╇━━━━━━━━━━━━━━━━━━━━━━━━┩ │
│         │ │ my_asset │ my_group │      │       │ Asset that greets you. │ │
│         │ └──────────┴──────────┴──────┴───────┴────────────────────────┘ │
└─────────┴─────────────────────────────────────────────────────────────────┘