Fix: Handle JSON dtype in anywidget display

This commit fixes an AttributeError that occurred when displaying a
DataFrame with a JSON column in anywidget mode. The dtype check
was incorrect and has been updated. Additionally, the SQL compilation
for casting JSON to string has been corrected to use TO_JSON_STRING.

Author: shuoweil

bigframes/core/compile/ibis_compiler/scalar_op_registry.py

@@ -1036,7 +1036,7 @@ def astype_op_impl(x: ibis_types.Value, op: ops.AsTypeOp):
         if to_type == ibis_dtypes.bool:
             return cast_json_to_bool_in_safe(x) if op.safe else cast_json_to_bool(x)
         if to_type == ibis_dtypes.string:
-            return cast_json_to_string_in_safe(x) if op.safe else cast_json_to_string(x)
+            return to_json_string(x)
 
     # TODO: either inline this function, or push rest of this op into the function
     return bigframes.core.compile.ibis_types.cast_ibis_value(x, to_type, safe=op.safe)

bigframes/display/anywidget.py

@@ -62,7 +62,20 @@ def __init__(self, dataframe: bigframes.dataframe.DataFrame):
             )
 
         super().__init__()
-        self._dataframe = dataframe
+        # Workaround for Arrow bug https://github.com/apache/arrow/issues/45262
+        # JSON columns are not supported in `to_pandas_batches` and will be converted to string.
+        json_cols = [
+            col
+            for col, dtype in dataframe.dtypes.items()
+            if dtype == bigframes.dtypes.JSON_DTYPE
+        ]
+        if json_cols:
+            df_copy = dataframe.copy()
+            for col in json_cols:
+                df_copy[str(col)] = df_copy[str(col)].astype("string")
+            self._dataframe = df_copy
+        else:
+            self._dataframe = dataframe
 
         # Initialize attributes that might be needed by observers FIRST
         self._table_id = str(uuid.uuid4())
@@ -191,9 +204,6 @@ def _reset_batches_for_new_page_size(self):
 
     def _set_table_html(self):
         """Sets the current html data based on the current page and page size."""
-        # TODO (shuowei): BigFrames Series with db_dtypes.JSONArrowType column
-        # fails to convert to pandas DataFrame in anywidget environment due to
-        # missing handling in to_pandas_batches(). b/453561268
         # For empty dataframe, render empty table with headers.
         if self.row_count == 0:
             page_data = self._cached_data