docs: Update multimodal notebook to use internal runtime helper

Author: shuoweil

notebooks/multimodal/multimodal_dataframe.ipynb

@@ -92,7 +92,7 @@
     },
     {
       "cell_type": "code",
-      "execution_count": 9,
+      "execution_count": null,
       "metadata": {
         "colab": {
           "base_uri": "https://localhost:8080/"
@@ -128,6 +128,38 @@
         "import bigframes.bigquery as bbq"
       ]
     },
+    {
+      "cell_type": "code",
+      "execution_count": null,
+      "metadata": {},
+      "outputs": [],
+      "source": [
+        "import bigframes.operations as ops\n",
+        "\n",
+        "def get_runtime_json_str(series, mode=\"R\", with_metadata=False):\n",
+        "    \"\"\"\n",
+        "    Get the runtime (contains signed URL to access gcs data) and apply the\n",
+        "    ToJSONSTring transformation.\n",
+        "    \n",
+        "    Args:\n",
+        "        series: bigframes.series.Series to operate on.\n",
+        "        mode: \"R\" for read, \"RW\" for read/write.\n",
+        "        with_metadata: Whether to fetch and include blob metadata.\n",
+        "    \"\"\"\n",
+        "    # 1. Optionally fetch metadata\n",
+        "    s = (\n",
+        "        series._apply_unary_op(ops.obj_fetch_metadata_op)\n",
+        "        if with_metadata\n",
+        "        else series\n",
+        "    )\n",
+        "    \n",
+        "    # 2. Retrieve the access URL runtime object\n",
+        "    runtime = s._apply_unary_op(ops.ObjGetAccessUrl(mode=mode))\n",
+        "    \n",
+        "    # 3. Convert the runtime object to a JSON string\n",
+        "    return runtime._apply_unary_op(ops.ToJSONString())"
+      ]
+    },
     {
       "cell_type": "markdown",
       "metadata": {
@@ -1638,7 +1670,7 @@
         "\n",
         "# Generate a JSON string containing the runtime information (including signed read URLs)\n",
         "# This allows the UDF to download the images from Google Cloud Storage\n",
-        "access_urls = exif_image_df[\"blob_col\"].blob.get_runtime_json_str(mode=\"R\")\n",
+        "access_urls = get_runtime_json_str(exif_image_df[\"blob_col\"], mode=\"R\")\n",
         "\n",
         "# Apply the BigQuery Python UDF to the runtime JSON strings\n",
         "# We cast to string to ensure the input matches the UDF's signature\n",
@@ -1670,7 +1702,7 @@
       "name": "python",
       "nbconvert_exporter": "python",
       "pygments_lexer": "ipython3",
-      "version": "3.13.0"
+      "version": "3.10.15"
     }
   },
   "nbformat": 4,