fix: cache DataFrames to temp tables in bigframes.bigquery.ml methods to avoid time travel (#2318)

See internal issue b/310266666 🦕

Author: tswast

bigframes/bigquery/_operations/ml.py

@@ -39,6 +39,10 @@ def _to_sql(df_or_sql: Union[pd.DataFrame, dataframe.DataFrame, str]) -> str:
 else:
 bf_df=cast(dataframe.DataFrame, df_or_sql)
 
+# Cache dataframes to make sure base table is not a snapshot.
+# Cached dataframe creates a full copy, never uses snapshot.
+# This is a workaround for internal issue b/310266666.
+bf_df.cache()
 sql, _, _=bf_df._to_sql_query(include_index=False)
 returnsql
 

bigframes/ml/core.py

@@ -436,8 +436,9 @@ def create_model(
  Returns: a BqmlModel, wrapping a trained model in BigQuery
  """
 options=dict(options)
-# Cache dataframes to make sure base table is not a snapshot
-# cached dataframe creates a full copy, never uses snapshot
+# Cache dataframes to make sure base table is not a snapshot.
+# Cached dataframe creates a full copy, never uses snapshot.
+# This is a workaround for internal issue b/310266666.
 ify_trainisNone:
 input_data=X_train.reset_index(drop=True).cache()
 else: