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Version: 1.4.1 (latest)

Propagate primary_key from root to nested tables

info

The source code for this example can be found in our repository at: https://github.com/dlt-hub/dlt/tree/devel/docs/examples/propagate_hints

About this Example

You learn how to propagate specific fields (e.g., primary, foreign keys) from a parent record into each child record.

In this example, we'll explore how to:

  • Add parent_id into each child record using add_parent_id function
  • Use the add_map function to apply this custom logic to every record in the dataset
important

Please note that dlt metadata, including _dlt_id and _dlt_load_id, will still be loaded into the tables.

Full source code

from typing import List, Dict, Any, Generator
import dlt


# Define a dlt resource with write disposition to 'merge'
@dlt.resource(name="parent_with_children", write_disposition={"disposition": "merge"})
def data_source() -> Generator[List[Dict[str, Any]], None, None]:
# Example data
data = [
{
"parent_id": 1,
"parent_name": "Alice",
"children": [
{"child_id": 1, "child_name": "Child 1"},
{"child_id": 2, "child_name": "Child 2"},
],
},
{
"parent_id": 2,
"parent_name": "Bob",
"children": [{"child_id": 3, "child_name": "Child 3"}],
},
]

yield data


# Function to add parent_id to each child record within a parent record
def add_parent_id(record: Dict[str, Any]) -> Dict[str, Any]:
parent_id_key = "parent_id"
for child in record["children"]:
child[parent_id_key] = record[parent_id_key]
return record


if __name__ == "__main__":
# Create and configure the dlt pipeline
pipeline = dlt.pipeline(
pipeline_name="generic_pipeline",
destination="duckdb",
dataset_name="dataset",
)

# Run the pipeline
load_info = pipeline.run(data_source().add_map(add_parent_id), primary_key="parent_id")
# Output the load information after pipeline execution
print(load_info)

This demo works on codespaces. Codespaces is a development environment available for free to anyone with a Github account. You'll be asked to fork the demo repository and from there the README guides you with further steps.
The demo uses the Continue VSCode extension.

Off to codespaces!

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