feat: Add BigQuery ML CREATE MODEL support

- Refactor `bigframes.core.sql` to a package.
- Add `bigframes.core.sql.ml` for DDL generation.
- Add `bigframes.bigquery.ml` module with `create_model` function.
- Add unit tests for SQL generation.
- Use `_start_query_ml_ddl` for execution.
- Return the created model object using `read_gbq_model`.
- Remove `query` argument, simplify SQL generation logic.
- Fix linting and mypy errors.

Author: google-labs-jules[bot]

bigframes/bigquery/_operations/ml.py

@@ -17,8 +17,8 @@
 import typing
 from typing import Mapping, Optional, Union
 
-import bigframes.core.sql.ml
 import bigframes.core.log_adapter as log_adapter
+import bigframes.core.sql.ml
 import bigframes.dataframe as dataframe
 import bigframes.ml.base
 import bigframes.session
@@ -59,7 +59,11 @@ def create_model(
     # Determine session from DataFrames if not provided
     if session is None:
         # Try to get session from inputs
-        dfs = [obj for obj in [training_data, custom_holiday] if hasattr(obj, "_session")]
+        dfs = [
+            obj
+            for obj in [training_data, custom_holiday]
+            if isinstance(obj, dataframe.DataFrame)
+        ]
         if dfs:
             session = dfs[0]._session
 

bigframes/core/sql/ml.py

@@ -20,6 +20,7 @@
 import bigframes.core.compile.googlesql as googlesql
 import bigframes.core.sql
 
+
 def create_model_ddl(
     model_name: str,
     *,
@@ -63,9 +64,9 @@ def create_model_ddl(
     # [REMOTE WITH CONNECTION {connection_name | DEFAULT}]
     if connection_name:
         if connection_name.upper() == "DEFAULT":
-             ddl += "REMOTE WITH CONNECTION DEFAULT\n"
+            ddl += "REMOTE WITH CONNECTION DEFAULT\n"
         else:
-             ddl += f"REMOTE WITH CONNECTION {googlesql.identifier(connection_name)}\n"
+            ddl += f"REMOTE WITH CONNECTION {googlesql.identifier(connection_name)}\n"
 
     # [OPTIONS(model_option_list)]
     if options:
@@ -77,7 +78,7 @@ def create_model_ddl(
                 # if value is list, it is [val1, val2]
                 rendered_val = bigframes.core.sql.simple_literal(list(option_value))
             else:
-                 rendered_val = bigframes.core.sql.simple_literal(option_value)
+                rendered_val = bigframes.core.sql.simple_literal(option_value)
 
             rendered_options.append(f"{option_name} = {rendered_val}")
 
@@ -93,7 +94,7 @@ def create_model_ddl(
             parts.append(f"custom_holiday AS ({custom_holiday})")
             ddl += f"AS (\n  {', '.join(parts)}\n)"
         else:
-             # Just training_data is treated as the query_statement
-             ddl += f"AS {training_data}"
+            # Just training_data is treated as the query_statement
+            ddl += f"AS {training_data}"
 
     return ddl