Support alternate string formatting strategies for external sources

README.md

@@ -234,8 +234,7 @@ FROM read_parquet(['s3://my-bucket/my-sources/source2a.parquet', 's3://my-bucket
 ```
 
 Note that the value of the `external_location` property does not need to be a path-like string; it can also be a function
-call, which is helpful in the case that you have an external source that is a CSV file which requires special handling for DuckDB
-to load it correctly:
+call, which is helpful in the case that you have an external source that is a CSV file which requires special handling for DuckDB to load it correctly:
 
 ```
 sources:
@@ -244,8 +243,18 @@ sources:
       - name: flights
         meta:
           external_location: "read_csv('flights.csv', types={'FlightDate': 'DATE'}, names=['FlightDate', 'UniqueCarrier'])"
+          formatter: oldstyle
 ```
 
+Note that we need to override the default `str.format` string formatting strategy for this example
+because the `types={'FlightDate': 'DATE'}` argument to the `read_csv` function will be interpreted by
+`str.format` as a template to be matched on, which will cause a `KeyError: "'FlightDate'"` when we attempt
+to parse the source in a dbt model. The `formatter` configuration option for the source indicates whether
+we should use `newstyle` string formatting (the default), `oldstyle` string formatting, or `template` string
+formatting. You can read up on the strategies the various string formatting techniques use at this
+[Stack Overflow answer](https://stackoverflow.com/questions/13451989/pythons-many-ways-of-string-formatting-are-the-older-ones-going-to-be-depre) and see examples of their use
+in this [dbt-duckdb integration test](https://github.com/jwills/dbt-duckdb/blob/master/tests/functional/adapter/test_sources.py).
+
 #### Writing to external files
 
 We support creating dbt models that are backed by external files via the `external` materialization strategy:

dbt/adapters/duckdb/relation.py

@@ -1,4 +1,5 @@
 from dataclasses import dataclass
+from string import Template
 from typing import Any
 from typing import Optional
 from typing import Type
@@ -26,12 +27,20 @@ def create_from_source(cls: Type[Self], source: SourceDefinition, **kwargs: Any)
             if DuckDBConnectionManager._ENV is not None:
                 # No connection means we are probably in the dbt parsing phase, so don't load yet.
                 DuckDBConnectionManager.env().load_source(plugin_name, source_config)
-        elif "external_location" in source_config.meta:
-            # Call str.format with the schema, name and identifier for the source so that they
-            # can be injected into the string; this helps reduce boilerplate when all
-            # of the tables in the source have a similar location based on their name
-            # and/or identifier.
-            ext_location = source_config["external_location"].format(**source_config.as_dict())
+        elif "external_location" in source_config:
+            ext_location_template = source_config["external_location"]
+            formatter = source_config.get("formatter", "newstyle")
+            if formatter == "newstyle":
+                ext_location = ext_location_template.format_map(source_config.as_dict())
+            elif formatter == "oldstyle":
+                ext_location = ext_location_template % source_config.as_dict()
+            elif formatter == "template":
+                ext_location = Template(ext_location_template).substitute(source_config.as_dict())
+            else:
+                raise ValueError(
+                    f"Formatter {formatter} not recognized. Must be one of 'newstyle', 'oldstyle', or 'template'."
+                )
+
             # If it's a function call or already has single quotes, don't add them
             if "(" not in ext_location and not ext_location.startswith("'"):
                 ext_location = f"'{ext_location}'"

tests/functional/adapter/test_sources.py

@@ -22,14 +22,20 @@
       - name: seeds_ost
         identifier: "seeds_other_source_table"
         config:
-          external_location: "read_csv_auto('/tmp/{identifier}.csv')"
+          external_location: "read_csv_auto('/tmp/%(identifier)s.csv')"
+          formatter: oldstyle
+      - name: seeds_other_source_table
+        config:
+          external_location: "read_csv_auto('/tmp/${name}.csv')"
+          formatter: template
 """
 
 models_source_model_sql = """select * from {{ source('external_source', 'seeds_source') }}
 """
 
-models_multi_source_model_sql = """select * from {{ source('external_source', 'seeds_source') }}
-  inner join {{ source('external_source', 'seeds_ost') }} USING (id)
+models_multi_source_model_sql = """select s.* from {{ source('external_source', 'seeds_source') }} s
+  inner join {{ source('external_source', 'seeds_ost') }} oldstyle USING (id)
+  inner join {{ source('external_source', 'seeds_other_source_table') }} tmpl USING (id)
 """