ExistingTableSource

fhir4ds.sources.ExistingTableSource — SourceAdapter for connections that already have a resources table or view loaded via FHIRDataLoader or any other mechanism.

Purpose

ExistingTableSource provides API uniformity for users who already load data with FHIRDataLoader. It wraps pre-loaded data in the same attach()/detach() lifecycle without changing your workflow or duplicating data.

Class Signature

ExistingTableSource(table_name: str = "resources")

Parameter	Type	Default	Description
table_name	str	"resources"	Name of the existing DuckDB table or view containing FHIR resources.

Raises: SchemaValidationError — if the existing table does not conform to the required schema (missing columns or wrong types).

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Methods

register(con)

• When table_name differs from "resources": creates a CREATE OR REPLACE VIEW resources projection over the named table.
• When table_name is "resources": skips view creation and runs schema validation directly.

Always calls validate_schema() before returning.

unregister(con)

Drops the resources view only if it was created by this adapter (i.e., when table_name was not "resources"). Safe to call even if register() was never called.

supports_incremental()

Returns False. ExistingTableSource does not support incremental delta tracking.

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Examples

Wrapping the Default resources Table

import fhir4ds
from fhir4ds.cql.loader import FHIRDataLoader
from fhir4ds.sources import ExistingTableSource

con = fhir4ds.create_connection()

# Load data the traditional way
loader = FHIRDataLoader(con)
loader.load_directory('/data/fhir/')

# Wrap with the adapter API — validates schema immediately
source = ExistingTableSource()
fhir4ds.attach(con, source)

Wrapping a Custom-Named Table

# If your table is named something other than 'resources'
source = ExistingTableSource("my_fhir_table")
fhir4ds.attach(con, source)
# Now a 'resources' view exists that projects from 'my_fhir_table'

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When to Use This vs FHIRDataLoader Directly

Scenario	Recommendation
You want the simplest possible workflow	Use FHIRDataLoader directly — no adapter needed
You want a uniform API across all data sources	Wrap with ExistingTableSource
You're migrating to source adapters incrementally	ExistingTableSource is the bridge
You need to swap data sources dynamically	Use adapters with attach()/detach()