HotFix: PG to PG is empty bug (#130)

There was an inconsistency with the types returned from postgres and
those being passed in.

PG.fetch returned `DataFrame`
but 
PG.save expected `TypedDataFrame`

Resulted in a bug where data.is_empty did not exist. 

This PR aligns the types naively, but this will all be improved in a
follow up #129 (which assigns proper/non-empty types) to Postgres
dataframes.

config.yaml

@@ -48,3 +48,11 @@ jobs:
       ref: PG
       table_name: cow.solvers
       if_exists: replace
+
+  - name: p2p-test
+    source:
+      ref: PG
+      query_string: "SELECT 1 as number, '\\x1234'::bytea as my_bytes;"
+    destination:
+      ref: PG
+      table_name: moo.p2p-test

src/sources/postgres.py

@@ -9,7 +9,7 @@
 from sqlalchemy import create_engine, text
 from sqlalchemy.exc import SQLAlchemyError
 
-from src.interfaces import Source
+from src.interfaces import Source, TypedDataFrame
 from src.logger import log
 
 
@@ -41,7 +41,7 @@ def _convert_bytea_to_hex(df: DataFrame) -> DataFrame:
     return df
 
 
-class PostgresSource(Source[DataFrame]):
+class PostgresSource(Source[TypedDataFrame]):
     """Represent PostgreSQL as a data source for retrieving data via SQL queries.
 
     This class connects to a PostgreSQL database using SQLAlchemy and executes a query
@@ -100,7 +100,7 @@ def validate(self) -> bool:
             log.error("Invalid SQL query: %s", str(e))
             return False
 
-    async def fetch(self) -> DataFrame:
+    async def fetch(self) -> TypedDataFrame:
         """Execute the SQL query and retrieves the result as a DataFrame.
 
         Returns
@@ -121,9 +121,10 @@ async def fetch(self) -> DataFrame:
         df = await loop.run_in_executor(
             None, lambda: pd.read_sql_query(self.query_string, con=self.engine)
         )
-        return _convert_bytea_to_hex(df)
+        # TODO include types.
+        return TypedDataFrame(dataframe=_convert_bytea_to_hex(df), types={})
 
-    def is_empty(self, data: DataFrame) -> bool:
+    def is_empty(self, data: TypedDataFrame) -> bool:
         """Check if the provided DataFrame is empty.
 
         Parameters
@@ -137,7 +138,7 @@ def is_empty(self, data: DataFrame) -> bool:
             True if the DataFrame is empty, False otherwise.
 
         """
-        return data.empty
+        return data.is_empty()
 
     def _set_query_string(self, query_string: str) -> None:
         """Set the SQL query string directly or from a file if it ends with '.sql'.

tests/unit/sources_test.py

@@ -9,6 +9,7 @@
 from sqlalchemy.dialects.postgresql import BYTEA
 
 from src.config import RuntimeConfig
+from src.interfaces import TypedDataFrame
 from src.sources.dune import _reformat_varbinary_columns, dune_result_to_df
 from src.sources.postgres import PostgresSource, _convert_bytea_to_hex
 from tests import config_root, fixtures_root
@@ -136,5 +137,4 @@ def test_is_empty(self):
             db_url="postgresql://postgres:postgres@localhost:5432/postgres",
             query_string="SELECT 1",
         )
-        df = pd.DataFrame([])
-        self.assertTrue(src.is_empty(df))
+        self.assertTrue(src.is_empty(TypedDataFrame(pd.DataFrame([]), {})))