This reference page provides information for working with dagster-snowflake features that are not covered as part of the Using Dagster with Snowflake tutorial.
In addition to password-based authentication, you can authenticate with Snowflake using a key pair. To set up private key authentication for your Snowflake account, see the instructions in the Snowflake docs. Currently, the Snowflake I/O manager only supports encrypted private keys.
You can provide the private key directly to the Snowflake I/O manager, or via a file containing the private key.
from dagster_snowflake_pandas import snowflake_pandas_io_manager from dagster import Definitions defs = Definitions( assets=[iris_dataset], resources={ "io_manager": snowflake_pandas_io_manager.configured( { "account": "abc1234.us-east-1", "user": {"env": "SNOWFLAKE_USER"}, "private_key": {"env": "SNOWFLAKE_PK"}, "private_key_password": {"env": "SNOWFLAKE_PK_PASSWORD"}, "database": "FLOWERS", } ) }, )
Sometimes you may not want to fetch an entire table as the input to a downstream asset. With the Snowflake I/O manager, you can select specific columns to load by supplying metadata on the downstream asset.
import pandas as pd from dagster import AssetIn, asset # this example uses the iris_dataset asset from Step 2 of the Using Dagster with Snowflake tutorial @asset( ins={ "iris_sepal": AssetIn( key="iris_dataset", metadata={"columns": ["Sepal length (cm)", "Sepal width (cm)"]}, ) } ) def sepal_data(iris_sepal: pd.DataFrame) -> pd.DataFrame: iris_sepal["Sepal area (cm2)"] = ( iris_sepal["Sepal length (cm)"] * iris_sepal["Sepal width (cm)"] ) return iris_sepal
In this example, we only use the columns containing sepal data from the IRIS_DATASET table created in Step 2: Create tables in Snowflake of the Using Dagster with Snowflake tutorial. Fetching the entire table would be unnecessarily costly, so to select specific columns, we can add metadata to the input asset. We do this in the metadata parameter of the AssetIn that loads the iris_dataset asset in the ins parameter. We supply the key columns with a list of names of the columns we want to fetch.
When Dagster materializes sepal_data and loads the iris_dataset asset using the Snowflake I/O manager, it will only fetch the Sepal length (cm) and Sepal width (cm) columns of the FLOWERS.IRIS.IRIS_DATASET table and pass them to sepal_data as a Pandas DataFrame.
The Snowflake I/O manager supports storing and loading partitioned data. In order to correctly store and load data from the Snowflake table, the Snowflake I/O manager needs to know which column contains the data defining the partition bounds. The Snowflake I/O manager uses this information to construct the correct queries to select or replace the data. In the following sections, we describe how the I/O manager constructs these queries for different types of partitions.
In order to store static partitioned assets in Snowflake, you must specify partition_expr metadata on the asset to tell the Snowflake I/O manager which column contains the partition data:
import pandas as pd from dagster import StaticPartitionDefinition, asset @asset( partitions_def=StaticPartitionDefinition( ["Iris-setosa", "Iris-virginica", "Iris-versicolor"] ), metadata={"partition_expr": "SPECIES"}, ) def iris_dataset_partitioned(context) -> pd.DataFrame: species = context.asset_partition_key_for_output() full_df = pd.read_csv( "https://archive.ics.uci.edu/ml/machine-learning-databases/iris/iris.data", names=[ "Sepal length (cm)", "Sepal width (cm)", "Petal length (cm)", "Petal width (cm)", "Species", ], ) return full_df[full_df["Species"] == species] @asset def iris_cleaned(iris_dataset_partitioned: pd.DataFrame): return iris_dataset_partitioned.dropna().drop_duplicates()
Dagster uses the partition_expr metadata to craft the SELECT statement when loading the partition in the downstream asset. When loading a static partition (or multiple static partitions), the following statement is used:
SELECT * WHERE [partition_expr] in ([selected partitions])
When the partition_expr value is injected into this statement, the resulting SQL query must follow Snowflake's SQL syntax. Refer to the Snowflake documentation for more information.
When materializing the above assets, a partition must be selected, as described in Materializing partitioned assets. In this example, the query used when materializing the Iris-setosa partition of the above assets would be:
SELECT * WHERE SPECIES in ('Iris-setosa')
Like static partitioned assets, you can specify partition_expr metadata on the asset to tell the Snowflake I/O manager which column contains the partition data:
import pandas as pd from dagster import DailyPartitionsDefinition, asset @asset( partitions_def=DailyPartitionsDefinition(start_date="2023-01-01"), metadata={"partition_expr": "TO_TIMESTAMP(time::INT)"}, ) def iris_data_per_day(context) -> pd.DataFrame: partition = context.asset_partition_key_for_output() # get_iris_data_for_date fetches all of the iris data for a given date, # the returned dataframe contains a column named 'time' with that stores # the time of the row as an integer of seconds since epoch return get_iris_data_for_date(partition) @asset def iris_cleaned(iris_data_per_day: pd.DataFrame): return iris_data_per_day.dropna().drop_duplicates()
Dagster uses the partition_expr metadata to craft the SELECT statement when loading the correct partition in the downstream asset. When loading a dynamic partition, the following statement is used:
SELECT * WHERE [partition_expr] >= [partition_start] AND [partition_expr] < [partition_end]
When the partition_expr value is injected into this statement, the resulting SQL query must follow Snowflake's SQL syntax. Refer to the Snowflake documentation for more information.
When materializing the above assets, a partition must be selected, as described in Materializing partitioned assets. The [partition_start] and [partition_end] bounds are of the form YYYY-MM-DD HH:MM:SS. In this example, the query when materializing the 2023-01-02 partition of the above assets would be:
SELECT * WHERE TO_TIMESTAMP(time::INT) >= '2023-01-02 00:00:00' AND TO_TIMESTAMP(time::INT) < '2023-01-03 00:00:00'
In this example, the data in the TIME column are integers, so the partition_expr metadata includes a SQL statement to convert integers to timestamps. A full list of Snowflake functions can be found here.
The Snowflake I/O manager can also store data partitioned on multiple dimensions. To do this, you must specify the column for each partition as a dictionary of partition_expr metadata:
import pandas as pd from dagster import ( DailyPartitionsDefinition, MultiPartitionsDefinition, StaticPartitionDefinition, asset, ) @asset( partitions_def=MultiPartitionsDefinition( { "date": DailyPartitionsDefinition(start_date="2023-01-01"), "species": StaticPartitionDefinition( ["Iris-setosa", "Iris-virginica", "Iris-versicolor"] ), } ), metadata={ "partition_expr": {"date": "TO_TIMESTAMP(time::INT)", "species": "SPECIES"} }, ) def iris_dataset_partitioned(context) -> pd.DataFrame: partition = partition = context.partition_key.keys_by_dimension species = partition["species"] date = partition["date"] # get_iris_data_for_date fetches all of the iris data for a given date, # the returned dataframe contains a column named 'time' with that stores # the time of the row as an integer of seconds since epoch full_df = get_iris_data_for_date(date) return full_df[full_df["Species"] == species] @asset def iris_cleaned(iris_dataset_partitioned: pd.DataFrame): return iris_dataset_partitioned.dropna().drop_duplicates()
Dagster uses the partition_expr metadata to craft the SELECT statement when loading the correct partition in a downstream asset. For multi-partitions, Dagster concatenates the WHERE statements described in the above sections to craft the correct SELECT statement.
When materializing the above assets, a partition must be selected, as described in Materializing partitioned assets. For example, when materializing the 2023-01-02|Iris-setosa partition of the above assets, the following query will be used:
SELECT * WHERE SPECIES = 'Iris-setosa' AND TO_TIMESTAMP(time::INT) >= '2023-01-02 00:00:00' AND TO_TIMESTAMP(time::INT) < '2023-01-03 00:00:00'`
You may want to have different assets stored in different Snowflake schemas. The Snowflake I/O manager allows you to specify the schema in several ways.
If you want all of your assets to be stored in the same schema, you can specify the schema as configuration to the I/O manager, like we did in Step 1: Configure the Snowflake I/O manager of the Using Dagster with Snowflake tutorial.
If you want to store assets in different schemas, you can specify the schema as part of the the asset's asset key:
import pandas as pd from dagster import SourceAsset, asset daffodil_dataset = SourceAsset(key=["daffodil", "daffodil_dataset"]) @asset(key_prefix=["iris"]) def iris_dataset() -> pd.DataFrame: return pd.read_csv( "https://archive.ics.uci.edu/ml/machine-learning-databases/iris/iris.data", names=[ "Sepal length (cm)", "Sepal width (cm)", "Petal length (cm)", "Petal width (cm)", "Species", ], )
In this example, the iris_dataset asset will be stored in the IRIS schema, and the daffodil_dataset asset will be found in the DAFFODIL schema.
The two options for specifying schema are mutually exclusive. If you provide schema configuration to the I/O manager, you cannot also provide it via the asset key and vice versa. If no schema is provided, either from configuration or asset keys, the default schema PUBLIC will be used.
You may have assets that you don't want to store in Snowflake. You can provide an I/O manager to each asset using the io_manager_key parameter in the asset decorator:
import pandas as pd from dagster_aws.s3.io_manager import s3_pickle_io_manager from dagster_snowflake_pandas import snowflake_pandas_io_manager from dagster import Definitions, asset @asset(io_manager_key="warehouse_io_manager") def iris_dataset() -> pd.DataFrame: return pd.read_csv( "https://archive.ics.uci.edu/ml/machine-learning-databases/iris/iris.data", names=[ "Sepal length (cm)", "Sepal width (cm)", "Petal length (cm)", "Petal width (cm)", "Species", ], ) @asset(io_manager_key="blob_io_manager") def iris_plots(iris_dataset): # plot_data is a function we've defined somewhere else # that plots the data in a DataFrame return plot_data(iris_dataset) defs = Definitions( assets=[iris_dataset, iris_plots], resources={ "warehouse_io_manager": snowflake_pandas_io_manager.configured( { "database": "FLOWERS", "schema": "IRIS", "account": "abc1234.us-east-1", "user": {"env": "SNOWFLAKE_USER"}, "password": {"env": "SNOWFLAKE_PASSWORD"}, } ), "blob_io_manager": s3_pickle_io_manager, }, )
In this example, the iris_dataset asset uses the I/O manager bound to the key warehouse_io_manager and iris_plots will use the I/O manager bound to the key blob_io_manager. In the Definitions object, we supply the I/O managers for those keys. When materialize these assets, the iris_dataset will get stored in Snowflake, and iris_plots will get saved in S3.
The Snowflake I/O manager also supports storing and loading PySpark DataFrames. To use the snowflake_pyspark_io_manager, first install the package:
pip install dagster-snowflake-pyspark
Then you can use the snowflake_pyspark_io_manager in your Definitions as in Step 1: Configure the Snowflake I/O manager of the Using Dagster with Snowflake tutorial.
from dagster_snowflake_pyspark import snowflake_pyspark_io_manager from dagster import Definitions defs = Definitions( assets=[iris_dataset], resources={ "io_manager": snowflake_pyspark_io_manager.configured( { "account": "abc1234.us-east-1", # required "user": {"env": "SNOWFLAKE_USER"}, # required "password": {"env": "SNOWFLAKE_PASSWORD"}, # required "database": "FLOWERS", # required "warehouse": "PLANTS", # required for pyspark "role": "writer", # optional, defaults to the default role for the account "schema": "IRIS", # optional, defaults to PUBLIC } ) }, )
When using the snowflake_pyspark_io_manager the warehouse configuration is required.
The snowflake_pyspark_io_manager requires that a SparkSession be active and configured with the Snowflake connector for Spark. You can either create your own SparkSession or use the spark_resource.
from dagster_pyspark import pyspark_resource from dagster_snowflake_pyspark import snowflake_pyspark_io_manager from pyspark import SparkFiles from pyspark.sql import ( DataFrame, SparkSession, ) from pyspark.sql.types import ( DoubleType, StringType, StructField, StructType, ) from dagster import Definitions, asset SNOWFLAKE_JARS = "net.snowflake:snowflake-jdbc:3.8.0,net.snowflake:spark-snowflake_2.12:2.8.2-spark_3.0" @asset(required_resource_keys={"pyspark"}) def iris_dataset(context) -> DataFrame: spark = context.resources.pyspark.spark_session schema = StructType( [ StructField("Sepal length (cm)", DoubleType()), StructField("Sepal width (cm)", DoubleType()), StructField("Petal length (cm)", DoubleType()), StructField("Petal width (cm)", DoubleType()), StructField("Species", StringType()), ] ) url = "https://archive.ics.uci.edu/ml/machine-learning-databases/iris/iris.data" spark.sparkContext.addFile(url) return spark.read.schema(schema).csv("file://" + SparkFiles.get("iris.data")) defs = Definitions( assets=[iris_dataset], resources={ "io_manager": snowflake_pyspark_io_manager.configured( { "account": "abc1234.us-east-1", "user": {"env": "SNOWFLAKE_USER"}, "password": {"env": "SNOWFLAKE_PASSWORD"}, "database": "FLOWERS", "warehouse": "PLANTS", "schema": "IRIS", } ), "pyspark": pyspark_resource.configured( {"spark_conf": {"spark.jars.packages": SNOWFLAKE_JARS}} ), }, )
If you work with both Pandas and PySpark DataFrames and want a single I/O manager to handle storing and loading these DataFrames in Snowflake, you can construct a Snowflake I/O manager using build_snowflake_io_manager:
from dagster_snowflake import build_snowflake_io_manager from dagster_snowflake_pandas import SnowflakePandasTypeHandler from dagster_snowflake_pyspark import SnowflakePySparkTypeHandler from dagster import Definitions snowflake_io_manager = build_snowflake_io_manager( [SnowflakePandasTypeHandler(), SnowflakePySparkTypeHandler()] ) defs = Definitions( assets=[iris_dataset, rose_dataset], resources={ "io_manager": snowflake_io_manager.configured( { "account": "abc1234.us-east-1", "user": {"env": "SNOWFLAKE_USER"}, "password": {"env": "SNOWFLAKE_PASSWORD"}, "database": "FLOWERS", "warehouse": "PLANTS", "schema": "IRIS", } ) }, )
In addition to the Snowflake I/O manager, Dagster also provides a Snowflake resource for executing custom SQL queries.
from dagster_snowflake import snowflake_resource from dagster import Definitions, asset # this example executes a query against the IRIS_DATASET table created in Step 2 of the # Using Dagster with Snowflake tutorial @asset(required_resource_keys={"snowflake"}) def small_petals(context): return context.resources.snowflake.execute_query( ( 'SELECT * FROM IRIS_DATASET WHERE "Petal length (cm)" < 1 AND "Petal width' ' (cm)" < 1' ), fetch_results=True, use_pandas_result=True, ) defs = Definitions( assets=[small_petals], resources={ "snowflake": snowflake_resource.configured( { "account": "abc1234.us-east-1", "user": {"env": "SNOWFLAKE_USER"}, "password": {"env": "SNOWFLAKE_PASSWORD"}, "database": "FLOWERS", "schema": "IRIS,", } ) }, )
In this example, we attach the Snowflake resource to the small_petals asset. In the body of the asset function, we use the execute_query method of the resource to execute a custom SQL query against the IRIS_DATASET table created in Step 2: Create tables in Snowflake of the Using Dagster with Snowflake tutorial.
For more information on the Snowflake resource, including additional configuration settings, see the Snowflake resource API docs.