Valdas Druskinis
03/08/2024, 7:13 AMScout
03/08/2024, 7:13 AMdeps
parameter. However, in Dagster, dependencies between assets are specified using the ins
parameter, which defines the inputs to an asset function.
Here's a corrected version of your code snippet based on the documentation:
python
from dagster import asset, AssetIn
@asset(
name=f"bs_save_data_bq_{spec['table_name']}",
ins={"load_data": AssetIn(key=f"load_data_{spec['table_name']}")},
)
def _save_data_bq(context, load_data) -> MaterializeResult:
# Assuming load_data is a DataFrame
destination = spec["destination"]
unique_id = f"{spec['table_name']}_id"
# ... logic to save data to BigQuery ...
In this corrected version, the ins
parameter is used to specify that _save_data_bq
has an input named load_data
, which corresponds to the asset with the key f"load_data_{spec['table_name']}"
. The load_data
parameter in the function signature is then used to access the data produced by the upstream asset.
Please note that the MaterializeResult
type is not a standard return type for Dagster assets. Typically, an asset function would return the data that it produces, which could be a DataFrame or any other type of data. If you intend to use MaterializeResult
as a custom return type, make sure it is defined appropriately in your codebase.
Additionally, ensure that spec
is accessible within the scope of the asset function. If spec
is defined outside the function, it needs to be passed in a way that the asset function can access it, such as through a factory function pattern.
Remember to replace the comment # ... logic to save data to BigQuery ...
with the actual implementation code that saves the DataFrame to BigQuery using the bigquery
resource.
If you have further questions or need more detailed assistance, feel free to ask! Asset dependencies' names for assets cre... button "Couldn't find `AssetKey`" error when us... button resource with key 'bigquery' required by... button dagster-bigquery integration reference button Thank you for your feedback!Valdas Druskinis
03/08/2024, 7:17 AMScout
03/08/2024, 7:18 AMMERGE
statement, which is designed for upsert operations. This would offload more of the work to BigQuery and could simplify your code.
2. Error Handling: You are catching a NotFound
exception, which is good practice if the destination table might not exist. However, you may also want to handle other potential exceptions that could occur during the query or load operations.
3. Efficiency: Depending on the size of your datasets, merging dataframes in Python might be less efficient than performing set-based operations directly in BigQuery. If performance becomes an issue, consider using BigQuery's native capabilities for set operations.
4. Job Configuration: You are creating a LoadJobConfig
with write_disposition="WRITE_APPEND"
in both the try and except blocks. You could define this configuration once outside of the try-except block to avoid repetition.
5. Return Type: The MaterializeResult
type is not a standard Dagster return type. If this is a custom type you've defined, ensure that it's being used consistently across your assets. Typically, Dagster assets do not need to return a result unless the downstream assets require it.
6. Metadata: You are returning metadata with the number of records and a preview of the dataframe. This is a good practice for observability and debugging.
Here's a simplified version of your asset function that incorporates some of these suggestions:
```python
from dagster import asset, AssetIn, MetadataValue
from google.cloud import bigquery as bq
from google.cloud.exceptions import NotFound
@asset(
name=f"bs_save_data_bq_{spec['table_name']}",
ins={"load_data": AssetIn(key=f"load_data_{spec['table_name']}")},
)
def _save_data_bq(bigquery: BigQueryResource, load_data):
df = load_data
destination = spec["destination"]
unique_id = f"{spec['table_name']}_id"
job_config = bq.LoadJobConfig(write_disposition="WRITE_APPEND")
with bigquery.get_client() as client:
try:
# Use BigQuery's native upsert capabilities (e.g., MERGE statement) if possible
# ...
except NotFound:
# If the table does not exist, create it by loading the dataframe
job = client.load_table_from_dataframe(
dataframe=df,Scout
03/08/2024, 7:18 AMMERGE
statement. The MaterializeResult
return type has been replaced with a dictionary of metadata, which is more typical for Dagster assets. Remember to replace the comment with the actual implementation of the MERGE
statement or other BigQuery-native upsert logic. If you need further assistance with the specific SQL for the MERGE
statement or other improvements, please let me know!Valdas Druskinis
03/08/2024, 7:20 AMScout
03/08/2024, 7:20 AMMERGE
statement or other SQL queries that are not explicitly supported by the documentation. The MERGE
statement in BigQuery is a powerful SQL operation that allows you to perform insert, update, or delete operations on a target table based on the contents of a source table or a subquery. The general syntax for a MERGE
statement in BigQuery is as follows: sql MERGE target_table USING source_table ON merge_condition WHEN MATCHED THEN UPDATE SET column1 = value1, column2 = value2, ... WHEN NOT MATCHED THEN INSERT (column1, column2, ...) VALUES (value1, value2, ...)
To use the MERGE
statement in your Dagster asset, you would need to write a SQL query that defines the logic for how rows from your source DataFrame (load_data
) should be merged into the target BigQuery table (destination
). This involves specifying the conditions under which rows should be matched (e.g., by unique_id
) and what actions to take when there is a match or no match. Since I cannot provide the exact code, I recommend referring to the BigQuery documentation for MERGE
statements and constructing a query that fits your specific use case. Once you have your MERGE
statement, you can execute it using the BigQuery client within your Dagster asset, similar to how you would run any other query. If you encounter any issues while implementing this or have questions about Dagster-specific functionality, feel free to reach out for further assistance!Valdas Druskinis
03/08/2024, 7:30 AMScout
03/08/2024, 7:30 AMMERGE
statement in BigQuery using Python with the client.query()
method. You can construct the MERGE
SQL statement as a string in Python and then pass it to client.query()
to execute it. This approach allows you to use the full power of SQL within your Dagster asset without having to manually perform the merge logic in Python. Here's a conceptual example of how you might execute a MERGE
statement within a Dagster asset: python from dagster import asset, AssetIn from google.cloud import bigquery @asset( name=f"bs_save_data_bq_{spec['table_name']}", ins={"load_data": AssetIn(key=f"load_data_{spec['table_name']}")}, ) def _save_data_bq(bigquery: bigquery.Client, load_data): # Construct the MERGE SQL statement merge_sql = f""" MERGE `{spec['destination']}` T USING (SELECT * FROM UNNEST({load_data.to_gbq()}) S ON T.{spec['unique_id']} = S.{spec['unique_id']} WHEN MATCHED THEN UPDATE SET ... WHEN NOT MATCHED THEN INSERT (...) VALUES (...) """ # Execute the MERGE statement job = bigquery.query(merge_sql) job.result() # Wait for the query to finish # Return some metadata or result if needed return {"status": "completed"}
In this example, load_data.to_gbq()
is a placeholder for the method you would use to convert your DataFrame to a format that can be used in the USING
clause of the MERGE
statement. BigQuery's UNNEST
function is used here to flatten the array of rows for the merge operation. You will need to replace the ...
with the actual columns and values you want to update or insert. Please note that this is a conceptual example and may require adjustments to fit your specific use case. You will need to ensure that the DataFrame is in a suitable format for BigQuery and that the MERGE
statement is correctly constructed to match your schema and requirements. As for using dbt (data build tool), it is indeed another option for managing complex data transformations in BigQuery. dbt allows you to define data models, tests, and documentation, and it can handle MERGE
operations as part of its incremental models feature. If you have a workflow that involves multiple transformations and you want to manage it as code, dbt could be a good fit. You can invoke dbt runs from within Dagster assets or jobs if you want to integrate dbt into your Dagster workflows. Ultimately, whether you execute the MERGE
statement directly in Python or use dbt will depend on your preferences, the complexity of your data transformations, and how you want to manage your data pipeline code. Both approaches are valid and can be used effectively within a Dagster-managed pipeline.Valdas Druskinis
03/08/2024, 7:32 AMScout
03/08/2024, 7:32 AMDataFrame.to_gbq()
method is indeed used to write a DataFrame to a BigQuery table, and it requires the destination_table
argument. However, it's not suitable for use within a MERGE
statement as I previously suggested. To execute a MERGE
statement in BigQuery using Python, you would typically first load your DataFrame into a temporary table and then construct a MERGE
statement that uses this temporary table as the source for the merge operation. Here's a revised example that demonstrates this process: python from dagster import asset, AssetIn from google.cloud import bigquery @asset( name=f"bs_save_data_bq_{spec['table_name']}", ins={"load_data": AssetIn(key=f"load_data_{spec['table_name']}")}, ) def _save_data_bq(bigquery: bigquery.Client, load_data): # First, load the DataFrame into a temporary BigQuery table job_config = bigquery.LoadJobConfig(write_disposition="WRITE_TRUNCATE") job = bigquery.load_table_from_dataframe( dataframe=load_data, destination=f"{spec['destination']}_temp", job_config=job_config, ) job.result() # Wait for the job to complete # Construct the MERGE SQL statement using the temporary table merge_sql = f""" MERGE `{spec['destination']}` T USING `{spec['destination']}_temp` S ON T.{spec['unique_id']} = S.{spec['unique_id']} WHEN MATCHED THEN UPDATE SET ... WHEN NOT MATCHED THEN INSERT (...) VALUES (...) """ # Execute the MERGE statement merge_job = bigquery.query(merge_sql) merge_job.result() # Wait for the query to finish # Optionally, clean up the temporary table after the merge bigquery.delete_table(f"{spec['destination']}_temp") # Return some metadata or result if needed return {"status": "completed"}
In this revised example, the DataFrame load_data
is first loaded into a temporary BigQuery table. The write_disposition
parameter is set to WRITE_TRUNCATE
to ensure that the temporary table is overwritten if it already exists. After loading the DataFrame, a MERGE
statement is constructed that uses the temporary table as the source for the merge operation. After the MERGE
operation is complete, the temporary table is deleted. Please replace the ...
in the UPDATE SET
and INSERT
clauses with the actual logic for updating and inserting rows based on your schema. This approach allows you to perform the merge operation in BigQuery without having to manually handle the logic in Python, and it should work with the standard bigquery.Client
methods provided by the google-cloud-bigquery
library.Valdas Druskinis
03/08/2024, 7:34 AMScout
03/08/2024, 7:34 AMMERGE
statement within a dbt incremental model. dbt handles the incremental logic and can conditionally apply transformations to either insert new records or update existing ones based on a unique key.
Here's a high-level overview of how you might set up a dbt model to perform a merge operation in BigQuery:
1. Install dbt: Make sure you have dbt installed and configured for your BigQuery project.
2. Create a dbt Model: Define a new dbt model in your dbt project. This model will contain the SQL logic for the merge operation.
3. Use the Incremental Materialization: In the model's configuration, specify the materialization strategy as incremental
, which allows dbt to insert or update records based on a unique key.
4. Write the Merge Logic: In the model SQL file, write the logic for the MERGE
statement, using dbt's incremental model syntax to handle the conditional logic.
Here's an example of what the dbt model file might look like:
sql
-- models/my_merge_model.sql
{{ config(materialized='incremental', unique_key='unique_id') }}
WITH source_data AS (
-- Your logic to select or transform data that should be merged into the target table
)
MERGE INTO `{{ target.schema }}.target_table` AS target
USING source_data AS source
ON target.unique_id = source.unique_id
WHEN MATCHED THEN
UPDATE SET
target.column1 = source.column1,
target.column2 = source.column2
-- Add more columns as needed
WHEN NOT MATCHED THEN
INSERT (unique_id, column1, column2)
VALUES (source.unique_id, source.column1, source.column2)
-- Add more columns as needed
{% if is_incremental() %}
-- This condition will limit the merge to new or updated records
WHERE source.unique_id NOT IN (SELECT unique_id FROM `{{ target.schema }}.target_table`)
{% endif %}
In this example, replace unique_id
, column1
, column2
, etc., with the actual column names from your source and target tables. The {{ target.schema }}
variable is a dbt macro that resolves to the schema of the target table.
5. Run the dbt Model: Execute the dbt model using the dbt CLI with the following command:
sh
dbt run --models my_merge_model
This command will run the dbt model and apply the merge logic to your BigQuery table.
6. Integrate with Dagster: If you want to integrate dbt with Dagster, you can use Dagster's dbt integration to run dbt models as part of your Dagster workflows. You can define a Dagster asset that represents the dbt model and materialize it within a Dagster job.
Please note that the actual implementation details may vary based on your specific use case and dbt project setup. BeScout
03/08/2024, 7:34 AMMERGE
statement with BigQuery. Wrong Using dbt with Dagster tutorial co... button Creating dependencies between custom Op ... button Support dbt JSON output schemas across m... button How do I create an AssetSelection
of m... button Thank you for your feedback!Valdas Druskinis
03/08/2024, 9:15 AMScout
03/08/2024, 9:15 AMValdas Druskinis
03/08/2024, 9:16 AMScout
03/08/2024, 9:16 AM__init__.py
file in a way that is easily understandable and scalable, you can follow a structured approach where each section is clearly defined and logically organized. Here's a reorganized version of your __init__.py
file with comments explaining each section:
python
# __init__.py
# Imports and definitions
from dagster import load_assets_from_modules, define_asset_job
import test_assets
import test_category
import bs_assets
# Load singular assets from modules
singular_assets = load_assets_from_modules(
[
test_assets,
test_category,
]
)
# Generate factory pattern assets
generated_assets_bs = [bs_assets.generate_bs_assets(spec) for spec in bs_assets.specs]
generated_assets_bs_load = [item[0] for item in generated_assets_bs]
generated_assets_bs_save = [item[1] for item in generated_assets_bs]
quality_checks_bs = [item[2] for item in generated_assets_bs]
# Combine all assets
all_bs_assets = generated_assets_bs_load + generated_assets_bs_save
combined_assets = singular_assets + all_bs_assets
# Define jobs
test_job = define_asset_job(
"test_job",
selection=combined_assets,
)
# Define quality checks
# (Assuming you have a function or a way to define quality checks)
# quality_checks = define_quality_checks(quality_checks_bs)
# Define job schedules
# (Assuming you have a function or a way to define job schedules)
# job_schedules = define_job_schedules(test_job)
# Define resources
# (Assuming you have a function or a way to define resources)
# resources = define_resources()
# Combine all definitions
from dagster import Definitions
defs = Definitions(
assets=combined_assets,
jobs=[test_job],
# Uncomment and add the following lines as needed
# schedules=job_schedules,
# resources=resources,
# sensors=[...],
# ... other definitions ...
)
In this reorganized version, each section is clearly separated, and the assets are combined in a single list before being used in the job definition. This makes it easier to understand the flow and to add or remove components as needed.
A few things to note:
- The selection
parameter in define_asset_job
now directly uses combined_assets
. Ensure that combined_assets
contains the correct asset keys or names that the job should select.
- I've commented out the sections for quality checks, job schedules, and resources. You can define these in separate functions or modules and then import and use them in your __init__.py
file.
- The final Definitions
object defs
combines all the assets, jobs, and other components into a single definition that can be used by Dagster.
Remember to replace the placeholder comments and functions with your actual logic for defining quality checks, job schedules, and resources. This structurScout
03/08/2024, 9:17 AMValdas Druskinis
03/08/2024, 11:15 AMScout
03/08/2024, 11:15 AMpytest
and unittest.mock
for the factory function you provided:
python
import pandas as pd
from unittest.mock import patch, MagicMock
from dagster import build_input_context, build_output_context, AssetMaterialization
from your_module import generate_bs_assets # Replace with the actual module name
# Sample spec for testing
spec = {
'table_name': 'test_table',
'destination': 'your_dataset.your_table'
}
# Mock data to be used in tests
mock_df = pd.DataFrame({
'id': [1, 2, 3],
'value': ['A', 'B', 'C'],
'last_update': [pd.Timestamp.now()] * 3
})
# Test the load asset
def test_load_table():
load_table, _ = generate_bs_assets(spec)
with patch('pandas.read_csv') as mock_read_csv:
mock_read_csv.return_value = mock_df
result = load_table(azure_con=MagicMock())
mock_read_csv.assert_called_once_with(
f"/home/valdas/Documents/DE Exercise/to_csv/{spec['table_name']}.csv"
)
assert result.equals(mock_df), "DataFrames are not equal"
# Test the save asset
def test_save_data_bq():
_, save_data_bq = generate_bs_assets(spec)
mock_bigquery_resource = MagicMock()
mock_client = MagicMock()
mock_bigquery_resource.get_client.return_value.__enter__.return_value = mock_client
# Mock the BigQuery client behavior
mock_client.query.return_value.to_dataframe.return_value = pd.DataFrame({'id': []}) # No existing records
mock_client.load_table_from_dataframe.return_value.result.return_value = None # Mock job completion
with patch('google.cloud.bigquery.LoadJobConfig') as mock_job_config:
mock_job_config.return_value = MagicMock()
# Build input and output contexts for the asset
input_context = build_input_context(upstream_output=mock_df)
output_context = build_output_context()
# Execute the asset function
result = save_data_bq(bigquery=mock_bigquery_resource, load_data=input_context)
# Assertions to ensure the asset behaves as expected
assert isinstance(result, AssetMaterialization), "Result should be an AssetMaterialization"
assert result.metadata_entries[0].entry_data.text == str(len(mock_df)), "Metadata num_records should match DataFrame length"
In this example, we're using patch
to mock the pandas.read_csv
function and the BigQuery client interactions. We're also using build_input_context
and build_output_context
to create the necessScout
03/08/2024, 11:16 AMpytest
in your terminal. Please note that you'll need to adjust the paths and the mock data to match your actual data and environment. Additionally, you'll need to replace 'your_module'
with the actual name of the module where your generate_bs_assets
function is defined. This is a basic example to get you started. Depending on the complexity of your assets and the interactions they have with external systems, you may need to create more sophisticated mocks and assertions to fully test your assets' behavior.