fix: add missing handler for deserializing json value

google/cloud/bigquery/_helpers.py

@@ -17,6 +17,7 @@
 import base64
 import datetime
 import decimal
+import json
 import math
 import re
 import os
@@ -412,6 +413,12 @@ def _time_to_json(value):
     return value
 
 
+def _json_from_json(value, field):
+    """Coerce 'value' to a pythonic JSON representation, if set or not nullable."""
+    if _not_null(value, field):
+        return json.loads(value)
+
+
 # Converters used for scalar values marshalled as row data.
 _SCALAR_VALUE_TO_JSON_ROW = {
     "INTEGER": _int_to_json,
@@ -427,6 +434,7 @@ def _time_to_json(value):
     "DATETIME": _datetime_to_json,
     "DATE": _date_to_json,
     "TIME": _time_to_json,
+    "JSON": _json_from_json,
     # Make sure DECIMAL and BIGDECIMAL are handled, even though
     # requests for them should be converted to NUMERIC.  Better safe
     # than sorry.

google/cloud/bigquery/query.py

@@ -469,7 +469,7 @@ def to_api_repr(self) -> dict:
         value = self.value
         converter = _SCALAR_VALUE_TO_JSON_PARAM.get(self.type_)
         if converter is not None:
-            value = converter(value)
+            value = converter(value)  # type: ignore
         resource: Dict[str, Any] = {
             "parameterType": {"type": self.type_},
             "parameterValue": {"value": value},
@@ -626,7 +626,7 @@ def to_api_repr(self) -> dict:
 
             converter = _SCALAR_VALUE_TO_JSON_PARAM.get(a_type["type"])
             if converter is not None:
-                values = [converter(value) for value in values]
+                values = [converter(value) for value in values]  # type: ignore
             a_values = [{"value": value} for value in values]
 
         resource = {
@@ -775,7 +775,7 @@ def to_api_repr(self) -> dict:
                 s_types[name] = {"name": name, "type": {"type": type_}}
                 converter = _SCALAR_VALUE_TO_JSON_PARAM.get(type_)
                 if converter is not None:
-                    value = converter(value)
+                    value = converter(value)  # type: ignore
                 values[name] = {"value": value}
 
         resource = {

tests/unit/test__helpers.py

@@ -58,6 +58,24 @@ def test_w_float_value(self):
         self.assertEqual(coerced, 42)
 
 
+class Test_json_from_json(unittest.TestCase):
+    def _call_fut(self, value, field):
+        from google.cloud.bigquery._helpers import _json_from_json
+
+        return _json_from_json(value, field)
+
+    def test_w_none_nullable(self):
+        self.assertIsNone(self._call_fut(None, _Field("NULLABLE")))
+
+    def test_w_none_required(self):
+        with self.assertRaises(TypeError):
+            self._call_fut(None, _Field("REQUIRED"))
+
+    def test_w_string_value(self):
+        coerced = self._call_fut('{"foo": true}', object())
+        self.assertEqual(coerced, {"foo": True})
+
+
 class Test_float_from_json(unittest.TestCase):
     def _call_fut(self, value, field):
         from google.cloud.bigquery._helpers import _float_from_json