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Defining assets that depend on other assets

Asset definitions can depend on other asset definitions. The dependent asset is called the downstream asset, and the asset it depends on is the upstream asset.

Defining basic dependencies​

You can define a dependency between two assets by passing the upstream asset to the deps parameter in the downstream asset's @asset decorator.

In this example, the asset sugary_cereals creates a new table (sugary_cereals) by selecting records from the cereals table. Then the asset shopping_list creates a new table (shopping_list) by selecting records from sugary_cereals:

import dagster as dg


@dg.asset
def sugary_cereals() -> None:
    execute_query(
        "CREATE TABLE sugary_cereals AS SELECT * FROM cereals WHERE sugar_grams > 10"
    )


@dg.asset(deps=[sugary_cereals])
def shopping_list() -> None:
    execute_query("CREATE TABLE shopping_list AS SELECT * FROM sugary_cereals")

Defining asset dependencies across code locations​

Assets can depend on assets in different code locations. In the following example, the code_location_1_asset asset produces a JSON string from a file in code_location_1:

import json

import dagster as dg


@dg.asset
def code_location_1_asset():
    with open("/data/code_location_1_asset.json", "w+") as f:
        json.dump(5, f)


defs = dg.Definitions(assets=[code_location_1_asset])

In code_location_2, we can reference code_location_1_asset it via its asset key:

import json

import dagster as dg


@dg.asset(deps=["code_location_1_asset"])
def code_location_2_asset():
    with open("/data/code_location_1_asset.json") as f:
        x = json.load(f)

    with open("/data/code_location_2_asset.json", "w+") as f:
        json.dump(x + 6, f)