fix: configured refdata loader to be instantiated when required without class vars #99

Author: stevenhsd

CHANGELOG.md

@@ -1,8 +1,14 @@
+## v0.7.5 (2026-04-29)
+
+### Fix
+
+- configured refdata loader to be instantiated when required without need for class vars (#98)
+
 ## v0.7.4 (2026-04-17)
 
 ### Fix
 
-- fix failures not being properly audited in foundry pipeline
+- fix failures not being properly audited in foundry pipeline (#94)
 
 ## v0.7.3 (2026-04-16)
 

pyproject.toml

@@ -24,7 +24,7 @@ Issues = "https://github.com/NHSDigital/data-validation-engine/issues"
 Changelog = "https://github.com/NHSDigital/data-validation-engine/blob/main/CHANGELOG.md"
 
 [tool.poetry]
-version = "0.7.4"
+version = "0.7.5"
 packages = [
     { include = "dve", from = "src" },
 ]

src/dve/core_engine/backends/base/backend.py

@@ -3,7 +3,7 @@
 import logging
 import warnings
 from abc import ABC, abstractmethod
-from collections.abc import Mapping, MutableMapping
+from collections.abc import MutableMapping
 from typing import Any, ClassVar, Generic, Optional
 
 from pyspark.sql import DataFrame, SparkSession
@@ -41,14 +41,12 @@ def __init__(  # pylint: disable=unused-argument
         self,
         contract: BaseDataContract[EntityType],
         steps: BaseStepImplementations[EntityType],
-        reference_data_loader_type: Optional[type[BaseRefDataLoader[EntityType]]],
         logger: Optional[logging.Logger] = None,
         **kwargs: Any,
     ) -> None:
         for component_name, component in (
             ("Contract", contract),
             ("Step implementation", steps),
-            ("Reference data loader", reference_data_loader_type),
         ):
             component_entity_type = getattr(component, "__entity_type__", None)
             if component_entity_type != self.__entity_type__:
@@ -61,42 +59,16 @@ def __init__(  # pylint: disable=unused-argument
         """The data contract implementation used by the backend."""
         self.step_implementations = steps
         """The step implementations used by the backend."""
-        self.reference_data_loader_type = reference_data_loader_type
-        """
-        The loader type to use for the reference data. If `None`, do not
-        load any reference data and error if it is provided.
-
-        """
         self.logger = logger or get_logger(type(self).__name__)
         """The `logging.Logger instance for the backend."""
 
     def load_reference_data(
         self,
         reference_entity_config: dict[EntityName, ReferenceConfigUnion],
         submission_info: Optional[SubmissionInfo],
-    ) -> Mapping[EntityName, EntityType]:
-        """Load the reference data as specified in the reference entity config."""
-        sub_info_entity: Optional[EntityType] = None
-        if submission_info:
-            sub_info_entity = self.convert_submission_info(submission_info)
-
-        if self.reference_data_loader_type is None:
-            if reference_entity_config:
-                raise ValueError(
-                    "Reference data has been specified but no reference data loader is "
-                    + "configured for this backend"
-                )
-
-            reference_data_dict = {}
-            if sub_info_entity is not None:
-                reference_data_dict["dve_submission_info"] = sub_info_entity
-            return reference_data_dict
-
-        reference_data_loader = self.reference_data_loader_type(reference_entity_config)
-        if sub_info_entity is not None:
-            reference_data_loader.entity_cache["dve_submission_info"] = sub_info_entity
-
-        return reference_data_loader
+    ) -> BaseRefDataLoader[EntityType]:
+        """Supply configured reference data loader for use with business rules"""
+        raise NotImplementedError()
 
     @abstractmethod
     def convert_submission_info(self, submission_info: SubmissionInfo) -> EntityType:

src/dve/core_engine/backends/base/reference_data.py

@@ -11,6 +11,7 @@
 from dve.core_engine.backends.base.core import get_entity_type
 from dve.core_engine.backends.exceptions import (
     MissingRefDataEntity,
+    NoRefDataConfigSupplied,
     RefdataLacksFileExtensionSupport,
 )
 from dve.core_engine.backends.types import EntityType
@@ -147,11 +148,11 @@ class variable for the subclass.
     # pylint: disable=unused-argument
     def __init__(
         self,
-        reference_entity_config: dict[EntityName, ReferenceConfig],
-        dataset_config_uri: Optional[URI] = None,
+        reference_data_config: dict[EntityName, ReferenceConfig],
+        dataset_config_uri: URI,
         **kwargs,
     ) -> None:
-        self.reference_entity_config = reference_entity_config
+        self.reference_entity_config = reference_data_config
         self.dataset_config_uri = dataset_config_uri
         """
         Configuration options for the reference data. This is likely to vary
@@ -207,6 +208,8 @@ def __getitem__(self, key: EntityName) -> EntityType:
             try:
                 config = self.reference_entity_config[key]
                 return self.load_entity(entity_name=key, config=config)
+            except TypeError as err:
+                raise NoRefDataConfigSupplied() from err
             except Exception as err:
                 raise MissingRefDataEntity(entity_name=key) from err
 

src/dve/core_engine/backends/exceptions.py

@@ -119,6 +119,20 @@ def get_message_preamble(self) -> str:
         return f"Missing reference data entity {self.entity_name!r}"
 
 
+class NoRefDataConfigSupplied(BackendError):
+    """An error raised when trying to load a refdata entity when no refdata
+    config has been supplied.
+
+    """
+
+    def __init__(self, *args: object) -> None:
+        super().__init__(*args)
+
+    def get_message_preamble(self) -> EntityName:
+        """Message for logging purposes"""
+        return "Refdata loader not supplied with refdata config - unable to load refdata entities"
+
+
 class ConstraintError(ValueError, BackendErrorMixin):
     """Raised when a given constraint is violated."""
 

src/dve/core_engine/backends/implementations/duckdb/duckdb_helpers.py

@@ -411,7 +411,7 @@ def get_duckdb_cast_statement_from_annotation(
             stmt = rf"CASE WHEN REGEXP_MATCHES(TRIM({quoted_name}), '{date_regex}') THEN TRY_CAST(TRIM({quoted_name}) as DATE) ELSE NULL END"  # pylint: disable=C0301
             return stmt
         if issubclass(type_, time):
-            stmt = rf"CASE WHEN REGEXP_MATCHES(TRIM({quoted_name}), '{time_regex}') THEN TRY_CAST(TRIM({quoted_name}) as TIME) ELSE NULL END" # pylint: disable=C0301
+            stmt = rf"CASE WHEN REGEXP_MATCHES(TRIM({quoted_name}), '{time_regex}') THEN TRY_CAST(TRIM({quoted_name}) as TIME) ELSE NULL END"  # pylint: disable=C0301
             return stmt
         duck_type = get_duckdb_type_from_annotation(type_)
         if duck_type:

src/dve/core_engine/backends/implementations/duckdb/reference_data.py

@@ -1,13 +1,11 @@
 """A reference data loader for duckdb."""
 
-from typing import Optional
-
 from duckdb import DuckDBPyConnection, DuckDBPyRelation
 from pyarrow import ipc  # type: ignore
 
 from dve.core_engine.backends.base.reference_data import (
     BaseRefDataLoader,
-    ReferenceConfigUnion,
+    ReferenceConfig,
     ReferenceTable,
     mark_refdata_file_extension,
 )
@@ -19,17 +17,16 @@
 class DuckDBRefDataLoader(BaseRefDataLoader[DuckDBPyRelation]):
     """A reference data loader using already existing DuckDB tables."""
 
-    connection: DuckDBPyConnection
-    """The DuckDB connection for the backend."""
-    dataset_config_uri: Optional[URI] = None
-    """The location of the dischema file"""
-
     def __init__(
         self,
-        reference_entity_config: dict[EntityName, ReferenceConfigUnion],
+        connection: DuckDBPyConnection,
+        reference_data_config: dict[EntityName, ReferenceConfig],
+        dataset_config_uri: URI,
         **kwargs,
     ) -> None:
-        super().__init__(reference_entity_config, self.dataset_config_uri, **kwargs)
+        super().__init__(reference_data_config, dataset_config_uri, **kwargs)
+
+        self.connection = connection
 
         if not self.connection:
             raise AttributeError("DuckDBConnection must be specified")

src/dve/core_engine/backends/implementations/spark/backend.py

@@ -6,6 +6,7 @@
 from pyspark.sql import DataFrame, SparkSession
 
 from dve.core_engine.backends.base.backend import BaseBackend
+from dve.core_engine.backends.base.reference_data import ReferenceConfigUnion
 from dve.core_engine.backends.implementations.spark.contract import SparkDataContract
 from dve.core_engine.backends.implementations.spark.reference_data import SparkRefDataLoader
 from dve.core_engine.backends.implementations.spark.rules import SparkStepImplementations
@@ -14,7 +15,7 @@
 from dve.core_engine.constants import RECORD_INDEX_COLUMN_NAME
 from dve.core_engine.loggers import get_child_logger, get_logger
 from dve.core_engine.models import SubmissionInfo
-from dve.core_engine.type_hints import URI, EntityParquetLocations
+from dve.core_engine.type_hints import URI, EntityName, EntityParquetLocations
 from dve.parser.file_handling import get_resource_exists, joinuri
 
 
@@ -26,7 +27,6 @@ def __init__(
         dataset_config_uri: Optional[URI] = None,
         contract: Optional[SparkDataContract] = None,
         steps: Optional[SparkStepImplementations] = None,
-        reference_data_loader: Optional[type[SparkRefDataLoader]] = None,
         logger: Optional[logging.Logger] = None,
         spark_session: Optional[SparkSession] = None,
         **kwargs: Any,
@@ -36,6 +36,8 @@ def __init__(
 
         self.spark_session = spark_session or SparkSession.builder.getOrCreate()
         """The Spark session for the backend."""
+        self.dataset_config_uri = dataset_config_uri
+        """The uri of the dischema specifying the DVE config"""
 
         if contract is None:
             contract = SparkDataContract(
@@ -46,11 +48,27 @@ def __init__(
             steps = SparkStepImplementations.register_udfs(
                 logger=get_child_logger("SparkStepImplementations", logger)
             )
-        if reference_data_loader is None:
-            reference_data_loader = SparkRefDataLoader
-        reference_data_loader.spark = self.spark_session
-        reference_data_loader.dataset_config_uri = dataset_config_uri
-        super().__init__(contract, steps, reference_data_loader, logger, **kwargs)
+        super().__init__(contract, steps, logger, **kwargs)
+
+    def load_reference_data(
+        self,
+        reference_entity_config: dict[EntityName, ReferenceConfigUnion],
+        submission_info: Optional[SubmissionInfo],
+    ):
+        """Load the reference data as specified in the reference entity config."""
+        sub_info_entity: Optional[DataFrame] = None
+        if submission_info:
+            sub_info_entity = self.convert_submission_info(submission_info)
+
+        reference_data_loader = SparkRefDataLoader(
+            spark=self.spark_session,
+            reference_data_config=reference_entity_config,
+            dataset_config_uri=self.dataset_config_uri,  # type: ignore
+        )
+        if sub_info_entity is not None:
+            reference_data_loader.entity_cache["dve_submission_info"] = sub_info_entity
+
+        return reference_data_loader
 
     def write_entities_to_parquet(
         self, entities: SparkEntities, cache_prefix: URI

src/dve/core_engine/backends/implementations/spark/reference_data.py

@@ -1,8 +1,6 @@
 # pylint: disable=no-member
 """A reference data loader for Spark."""
 
-from typing import Optional
-
 from pyspark.sql import DataFrame, SparkSession
 
 from dve.core_engine.backends.base.reference_data import (
@@ -19,17 +17,15 @@
 class SparkRefDataLoader(BaseRefDataLoader[DataFrame]):
     """A reference data loader using already existing Apache Spark Tables."""
 
-    spark: SparkSession
-    """The Spark session for the backend."""
-    dataset_config_uri: Optional[URI] = None
-    """The location of the dischema file defining business rules"""
-
     def __init__(
         self,
-        reference_entity_config: dict[EntityName, ReferenceConfig],
+        spark: SparkSession,
+        reference_data_config: dict[EntityName, ReferenceConfig],
+        dataset_config_uri: URI,
         **kwargs,
     ) -> None:
-        super().__init__(reference_entity_config, self.dataset_config_uri, **kwargs)
+        super().__init__(reference_data_config, dataset_config_uri, **kwargs)
+        self.spark = spark
         if not self.spark:
             raise AttributeError("Spark session must be provided")
 

src/dve/pipeline/duckdb_pipeline.py

@@ -5,10 +5,12 @@
 
 from duckdb import DuckDBPyConnection, DuckDBPyRelation
 
-from dve.core_engine.backends.base.reference_data import BaseRefDataLoader
+import dve.parser.file_handling as fh
+from dve.core_engine.backends.base.reference_data import ReferenceConfig
 from dve.core_engine.backends.implementations.duckdb.auditing import DDBAuditingManager
 from dve.core_engine.backends.implementations.duckdb.contract import DuckDBDataContract
 from dve.core_engine.backends.implementations.duckdb.duckdb_helpers import duckdb_get_entity_count
+from dve.core_engine.backends.implementations.duckdb.reference_data import DuckDBRefDataLoader
 from dve.core_engine.backends.implementations.duckdb.rules import DuckDBStepImplementations
 from dve.core_engine.models import SubmissionInfo
 from dve.core_engine.type_hints import URI
@@ -30,7 +32,6 @@ def __init__(
         connection: DuckDBPyConnection,
         rules_path: Optional[URI],
         submitted_files_path: Optional[URI],
-        reference_data_loader: Optional[type[BaseRefDataLoader]] = None,
         job_run_id: Optional[int] = None,
         logger: Optional[logging.Logger] = None,
     ):
@@ -42,11 +43,20 @@ def __init__(
             DuckDBStepImplementations.register_udfs(connection=self._connection),
             rules_path,
             submitted_files_path,
-            reference_data_loader,
             job_run_id,
             logger,
         )
 
+    def init_reference_data_loader(
+        self, reference_data_config: dict[str, ReferenceConfig], **kwargs
+    ) -> DuckDBRefDataLoader:
+        return DuckDBRefDataLoader(
+            connection=self._connection,
+            reference_data_config=reference_data_config,
+            dataset_config_uri=fh.get_parent(self._rules_path),  # type: ignore
+            **kwargs
+        )
+
     # pylint: disable=arguments-differ
     def write_file_to_parquet(  # type: ignore
         self, submission_file_uri: URI, submission_info: SubmissionInfo, output: URI