fix(ibis): implement workaround for empty json result

ibis-server/app/model/connector.py

@@ -1,12 +1,18 @@
+import base64
 import importlib
 from functools import cache
+from json import loads
 from typing import Any
 
 import ibis
+import ibis.backends.bigquery
 import ibis.expr.datatypes as dt
 import ibis.expr.schema as sch
+import ibis.formats
 import pandas as pd
 import sqlglot.expressions as sge
+from google.cloud import bigquery
+from google.oauth2 import service_account
 from ibis import BaseBackend
 from ibis.backends.sql.compilers.postgres import compiler as postgres_compiler
 
@@ -23,6 +29,8 @@ def __init__(self, data_source: DataSource, connection_info: ConnectionInfo):
             self._connector = MSSqlConnector(connection_info)
         elif data_source == DataSource.canner:
             self._connector = CannerConnector(connection_info)
+        elif data_source == DataSource.bigquery:
+            self._connector = BigQueryConnector(connection_info)
         else:
             self._connector = SimpleConnector(data_source, connection_info)
 
@@ -100,6 +108,40 @@ def _to_ibis_type(type_name: str) -> dt.DataType:
         return postgres_compiler.type_mapper.from_string(type_name)
 
 
+class BigQueryConnector(SimpleConnector):
+    def __init__(self, connection_info: ConnectionInfo):
+        super().__init__(DataSource.bigquery, connection_info)
+        self.connection_info = connection_info
+
+    def query(self, sql: str, limit: int) -> pd.DataFrame:
+        try:
+            return super().query(sql, limit)
+        except ValueError as e:
+            # Try to match the error message from the google cloud bigquery library matching Arrow type error.
+            # If the error message matches, requries to get the schema from the result and generate a empty pandas dataframe with the mapped schema
+            #
+            # It's a workaround for the issue that the ibis library does not support empty result for some special types (e.g. JSON or Interval)
+            # see details:
+            # - https://github.com/Canner/wren-engine/issues/909
+            # - https://github.com/ibis-project/ibis/issues/10612
+            if "Must pass schema" in str(e):
+                credits_json = loads(
+                    base64.b64decode(
+                        self.connection_info.credentials.get_secret_value()
+                    ).decode("utf-8")
+                )
+                credentials = service_account.Credentials.from_service_account_info(
+                    credits_json
+                )
+                client = bigquery.Client(credentials=credentials)
+                ibis_schema_mapper = ibis.backends.bigquery.BigQuerySchema()
+                bq_fields = client.query(sql).result()
+                ibis_fields = ibis_schema_mapper.to_ibis(bq_fields.schema)
+                return pd.DataFrame(columns=ibis_fields.names)
+            else:
+                raise e
+
+
 @cache
 def _get_pg_type_names(connection: BaseBackend) -> dict[int, str]:
     cur = connection.raw_sql("SELECT oid, typname FROM pg_type")

ibis-server/tests/routers/v2/connector/test_bigquery.py

@@ -198,6 +198,38 @@ async def test_query_values(client, manifest_str):
     assert response.status_code == 204
 
 
+async def test_query_empty_json(client, manifest_str):
+    # Test the empty result with json column
+    response = await client.post(
+        url=f"{base_url}/query",
+        json={
+            "manifestStr": manifest_str,
+            "connectionInfo": connection_info,
+            "sql": "select json_object('a', 1, 'b', 2) limit 0",
+        },
+    )
+    assert response.status_code == 200
+    result = response.json()
+    assert len(result["data"]) == 0
+    assert result["dtypes"] == {"f0_": "object"}
+
+    # Test only the json column is null
+    response = await client.post(
+        url=f"{base_url}/query",
+        json={
+            "manifestStr": manifest_str,
+            "connectionInfo": connection_info,
+            "sql": "select cast(null as JSON), 1",
+        },
+    )
+    assert response.status_code == 200
+    result = response.json()
+    assert len(result["data"]) == 1
+    assert result["data"][0][0] is None
+    assert result["data"][0][1] == 1
+    assert result["dtypes"] == {"f0_": "object", "f1_": "int64"}
+
+
 async def test_interval(client, manifest_str):
     response = await client.post(
         url=f"{base_url}/query",