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.

You can use the dg CLI to scaffold Dagster definitions such as assets, schedules, and sensors.

note

All definitions added underneath the defs directory of a project created with the create-dagster CLI will be automatically loaded into the top-level Definitions object.

Prerequisites

Before scaffolding definitions with dg, you must create a project with the create-dagster CLI and activate its virtual environment.

1. Scaffold an asset

You can use the dg scaffold defs 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 the asset has been scaffolded, we can see that a new file has been added to defs/assets, and view its contents:

tree

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

6 directories, 7 files

tree

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

6 directories, 6 files

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

import dagster as dg


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

tip

You can run dg scaffold defs from within any directory in your project and the resulting files will always be created in the <project-name>/src/<project_name>/defs/ folder.

2. Write an asset definition

In the above example, the scaffolded asset contains a basic commented-out definition. You can replace this definition with working code:

defs/assets/my_asset.py
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!")

3. Check your work

Finally, you 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. │ │
│         │ └──────────┴──────────┴──────┴───────┴────────────────────────┘ │
└─────────┴─────────────────────────────────────────────────────────────────┘

Prerequisites​

1. Scaffold an asset​

2. Write an asset definition​

3. Check your work​

Prerequisites

1. Scaffold an asset

2. Write an asset definition

3. Check your work