PipelineNode

laktory.models.pipeline.PipelineNode

Bases: BaseModel, PipelineChild

Pipeline base component generating a DataFrame by reading a data source and applying a transformer (chain of dataframe transformations). Optional output to a data sink.

Examples:

A node reading stock prices data from a CSV file and writing a DataFrame as a parquet file.

import io

import laktory as lk

node_yaml = '''
    name: brz_stock_prices
    source:
      path: "./events/stock_prices/"
      format: JSON
    sinks:
    - path: ./tables/brz_stock_prices/
      format: PARQUET
'''

node = lk.models.PipelineNode.model_validate_yaml(io.StringIO(node_yaml))

# node.execute()

A node reading stock prices from an upstream node and writing a DataFrame to a data table.

import io

import laktory as lk

node_yaml = '''
    name: slv_stock_prices
    source:
      node_name: brz_stock_prices
    sinks:
    - schema_name: finance
      table_name: slv_stock_prices
    transformer:
      nodes:
      - expr: |
            SELECT
              data.created_at AS created_at,
              data.symbol AS symbol,
              data.open AS open,
              data.close AS close,
              data.high AS high,
              data.low AS low,
              data.volume AS volume
            FROM
              {df}
      - func_name: drop_duplicates
        func_kwargs:
          subset:
            - symbol
            - timestamp
'''

node = lk.models.PipelineNode.model_validate_yaml(io.StringIO(node_yaml))

# node.execute()

References

---

• Data Pipeline

PARAMETER	DESCRIPTION
comment	Comment for the associated table or view TYPE: str | VariableType DEFAULT: None
dlt_template	Specify which template (notebook) to use when Databricks pipeline is selected as the orchestrator. TYPE: str | None | VariableType DEFAULT: 'DEFAULT'
execution_task_name_	Execution task name when orchestrator (such as Databricks Jobs and Airflow) supports multi-tasks execution. Nodes with the same task name will be executed together in a single task. If None is provided, node will be executed under node-{node-name}. TYPE: str | VariableType DEFAULT: None
expectations	List of data expectations. Can trigger warnings, drop invalid records or fail a pipeline. TYPE: list[DataQualityExpectation | VariableType] | VariableType DEFAULT: []
expectations_checkpoint_path_	Path to which the checkpoint file for which expectations on a streaming dataframe should be written. TYPE: str | Path | VariableType DEFAULT: None
name	Name given to the node. TYPE: str | VariableType
primary_keys	A list of column names that uniquely identify each row in the DataFrame. These columns are used to: - Document the uniqueness constraints of the node's output data. - Define the default primary keys for sinks CDC merge operations - Referenced in expectations and unit tests. While optional, specifying primary_keys helps enforce data integrity and ensures that downstream operations, such as deduplication, are consistent and reliable. TYPE: list[str | VariableType] | VariableType DEFAULT: None
root_path_	Location of the pipeline node root used to store logs, metrics and checkpoints. TYPE: str | Path | VariableType DEFAULT: None
sinks	Definition of the data sink(s). Set is_quarantine to True to store node quarantine DataFrame. TYPE: list[PipelineViewDataSink | FileDataSink | UnityCatalogDataSink | HiveMetastoreDataSink | VariableType] | VariableType DEFAULT: None
source	Definition of the data source(s) TYPE: CustomDataSource | FileDataSource | UnityCatalogDataSource | HiveMetastoreDataSource | DataFrameDataSource | PipelineNodeDataSource | None | VariableType DEFAULT: None
tags	Node tags for selective execution. TYPE: list[str | VariableType] | VariableType DEFAULT: []
time_column	The name of the column that represents the timestamp or temporal dimension in the DataFrame. This column is used to: - Document the time-based ordering and filtering semantics of the node’s output data. - Enable time-aware operations such as point-in-time joins, incremental processing, and time-series analysis. - Serve as a reference in expectations, unit tests, and feature engineering workflows. While optional, specifying time_column helps ensure consistency in time-based logic and improves the reliability of downstream operations that depend on temporal alignment. TYPE: str | None | VariableType DEFAULT: None
transformer	Data transformations applied between the source and the sink(s). TYPE: DataFrameTransformer | VariableType DEFAULT: None

METHOD	DESCRIPTION
check_expectations	Check expectations, raise errors, warnings where required and build
execute	Execute pipeline node by:

ATTRIBUTE	DESCRIPTION
all_sinks	List of all sinks (output and quarantine).
data_sources	Get all sources feeding the pipeline node TYPE: list[BaseDataSource]
has_output_sinks	True if node has at least one output sink. TYPE: bool
has_sinks	True if node has at least one sink. TYPE: bool
is_orchestrator_dlt	If True, pipeline node is used in the context of a DLT pipeline TYPE: bool
is_sql_expressible	True if the node can be executed on a SQL warehouse. TYPE: bool
output_df	Dataframe resulting from reading source, applying transformer and dropping rows not meeting data quality TYPE: AnyFrame
output_sinks	List of sinks writing the output DataFrame TYPE: list[DataSinksUnion]
primary_sink	Primary output sink used as a source for downstream nodes. TYPE: DataSinksUnion | None
quarantine_df	DataFrame storing stage_df rows not meeting data quality expectations. TYPE: AnyFrame
quarantine_sinks	List of sinks writing the quarantine DataFrame TYPE: list[DataSinksUnion]
sinks_count	Total number of sinks. TYPE: int
sql_statements	Generate one SQL statement per sink, suitable for execution on a SQL warehouse. TYPE: list[str]
stage_df	Dataframe resulting from reading source and applying transformer, before data quality checks are applied. TYPE: AnyFrame
upstream_node_names	Pipeline node names required to execute current node. TYPE: list[str]
view_definition	Transformer View Definition (when applicable)

all_sinks property

List of all sinks (output and quarantine).

data_sources property

Get all sources feeding the pipeline node

has_output_sinks property

True if node has at least one output sink.

has_sinks property

True if node has at least one sink.

is_orchestrator_dlt property

If True, pipeline node is used in the context of a DLT pipeline

is_sql_expressible property

True if the node can be executed on a SQL warehouse.

output_df property

Dataframe resulting from reading source, applying transformer and dropping rows not meeting data quality expectations.

output_sinks property

List of sinks writing the output DataFrame

primary_sink property

Primary output sink used as a source for downstream nodes.

quarantine_df property

DataFrame storing stage_df rows not meeting data quality expectations.

quarantine_sinks property

List of sinks writing the quarantine DataFrame

sinks_count property

Total number of sinks.

sql_statements property

Generate one SQL statement per sink, suitable for execution on a SQL warehouse.

Raises ValueError if the node is not SQL-expressible.

stage_df property

Dataframe resulting from reading source and applying transformer, before data quality checks are applied.

upstream_node_names property

Pipeline node names required to execute current node.

view_definition property

Transformer View Definition (when applicable)

check_expectations()

Check expectations, raise errors, warnings where required and build filtered and quarantine DataFrames.

Some actions have to be disabled when selected orchestrator is Databricks DLT:

• Raising error on Failure when expectation is supported by DLT
• Dropping rows when expectation is supported by DLT

Source code in laktory/models/pipeline/pipelinenode.py

def check_expectations(self):
    """
    Check expectations, raise errors, warnings where required and build
    filtered and quarantine DataFrames.

    Some actions have to be disabled when selected orchestrator is
    Databricks DLT:

    * Raising error on Failure when expectation is supported by DLT
    * Dropping rows when expectation is supported by DLT
    """

    # Data Quality Checks
    qfilter = None  # Quarantine filter
    kfilter = None  # Keep filter
    if self._stage_df is None:
        # Node without source or transformer
        return
    is_streaming = getattr(nw.to_native(self._stage_df), "isStreaming", False)
    if not self.expectations:
        return

    def _batch_check(df, node):
        for e in node.expectations:
            # Run Check: this only warn or raise exceptions.
            if not e.is_dlt_managed:
                e.run_check(
                    df,
                    raise_or_warn=True,
                    node=node,
                )

    def _stream_check(batch_df, batch_id, node):
        _batch_check(
            batch_df,
            node,
        )

    logger.info("Checking Data Quality Expectations")

    if not is_streaming:
        _batch_check(
            self._stage_df,
            self,
        )

    else:
        skip = False

        if self.is_dlt_execute:
            names = []
            for e in self.expectations:
                if not e.is_dlt_compatible:
                    names += [e.name]
            if names:
                raise TypeError(
                    f"Expectations {names} are not natively supported by DLT and can't be computed on a streaming DataFrame with DLT executor."
                )

            skip = True

        backend = DataFrameBackends.from_df(self._stage_df)
        if backend not in STREAMING_BACKENDS:
            raise TypeError(
                f"DataFrame backend {backend} is not supported for streaming operations"
            )

        if self.expectations_checkpoint_path is None:
            raise ValueError(
                f"Expectations Checkpoint not specified for node '{self.name}'"
            )

        # TODO: Refactor for backend other than spark
        if not skip:
            query = (
                self._stage_df.to_native()
                .writeStream.foreachBatch(
                    lambda batch_df, batch_id: _stream_check(
                        nw.from_native(batch_df), batch_id, self
                    )
                )
                .trigger(availableNow=True)
                .options(
                    checkpointLocation=self.expectations_checkpoint_path,
                )
                .start()
            )
            query.awaitTermination()

    # Build Filters
    for e in self.expectations:
        # Update Keep Filter
        if not e.is_dlt_managed:
            _filter = e.keep_filter
            if _filter is not None:
                if kfilter is None:
                    kfilter = _filter
                else:
                    kfilter = kfilter & _filter

        # Update Quarantine Filter
        _filter = e.quarantine_filter
        if _filter is not None:
            if qfilter is None:
                qfilter = _filter
            else:
                qfilter = qfilter & _filter

    if qfilter is not None:
        logger.info("Building quarantine DataFrame")
        self._quarantine_df = self._stage_df.filter(qfilter)
    else:
        self._quarantine_df = self._stage_df  # .filter("False")

    if kfilter is not None:
        logger.info("Dropping invalid rows")
        self._output_df = self._stage_df.filter(kfilter)
    else:
        self._output_df = self._stage_df

execute(apply_transformer=True, write_sinks=True, full_refresh=False, named_dfs=None, update_tables_metadata=True)

Execute pipeline node by:

• Reading the source
• Applying the user defined (and layer-specific if applicable) transformations
• Checking expectations
• Writing the sinks

PARAMETER	DESCRIPTION
apply_transformer	Flag to apply transformer in the execution TYPE: bool DEFAULT: True
write_sinks	Flag to include writing sink in the execution TYPE: bool DEFAULT: True
full_refresh	If True dataframe will be completely re-processed by deleting existing data and checkpoint before processing. TYPE: bool DEFAULT: False
named_dfs	Named DataFrame passed to transformer nodes TYPE: dict[str, AnyFrame] DEFAULT: None
update_tables_metadata	Update tables metadata TYPE: bool DEFAULT: True

RETURNS	DESCRIPTION
AnyFrame	output Spark DataFrame

Source code in laktory/models/pipeline/pipelinenode.py

def execute(
    self,
    apply_transformer: bool = True,
    write_sinks: bool = True,
    full_refresh: bool = False,
    named_dfs: dict[str, AnyFrame] = None,
    update_tables_metadata: bool = True,
) -> AnyFrame:
    """
    Execute pipeline node by:

    - Reading the source
    - Applying the user defined (and layer-specific if applicable) transformations
    - Checking expectations
    - Writing the sinks

    Parameters
    ----------
    apply_transformer:
        Flag to apply transformer in the execution
    write_sinks:
        Flag to include writing sink in the execution
    full_refresh:
        If `True` dataframe will be completely re-processed by deleting
        existing data and checkpoint before processing.
    named_dfs:
        Named DataFrame passed to transformer nodes
    update_tables_metadata:
        Update tables metadata

    Returns
    -------
    :
        output Spark DataFrame
    """
    logger.info(f"Executing pipeline node {self.name}")

    # Install dependencies
    pl = self.parent_pipeline
    if pl and not pl._imports_imported:
        for package_name in pl._imports:
            try:
                logger.info(f"Importing {package_name}")
                importlib.import_module(package_name)
            except ModuleNotFoundError:
                logger.info(f"Importing {package_name} failed.")
        pl._imports_imported = True

    # Parse DLT
    if self.is_orchestrator_dlt:
        logger.info("DLT orchestrator selected. Sinks writing will be skipped.")
        write_sinks = False
        full_refresh = False

    # Refresh
    if full_refresh:
        self.purge()

    # Read Source
    self._stage_df = None
    if self.source:
        self._stage_df = self.source.read()

    # Apply transformer
    if named_dfs is None:
        named_dfs = {}
    if apply_transformer and self.transformer:
        self._stage_df = self.transformer.execute(
            self._stage_df, named_dfs=named_dfs
        )

    # Check expectations
    self._output_df = self._stage_df
    self._quarantine_df = None
    self.check_expectations()

    # Output and Quarantine to Sinks
    if write_sinks and self.sinks:
        view_definition = self.view_definition

        for s in self.sinks:
            # Get DataFrame
            _df = self._output_df
            if s.is_quarantine:
                _df = self._quarantine_df

            # Create Sink
            s.create(df=_df)

            _is_update_metadata = (
                update_tables_metadata and s.metadata and not self.is_dlt_execute
            )

            if self.is_view:
                s.write(view_definition=view_definition)
                if _is_update_metadata:
                    s.metadata.execute()
                self._output_df = s.as_source().read()
            else:
                if _is_update_metadata:
                    s.metadata.execute()
                s.write(df=self._output_df)

                # Metadata update required because of schema overwrite
                if _is_update_metadata and s.metadata.update_required:
                    s.metadata.execute()

    return self._output_df