Repository: googleapis/python-bigquery (python)

Issue:
BigQuery: complex repeated schema fields are slow
When converting rows to JSON, repeated schema fields are deepcopied causing noticeable slowdowns in complex schemas.
Since conversion is performed recursively, complex schemas containing multiple levels of repeated fields (e.g. repeated list of structs each containing multiple fields of repeated structs) are copied multiple times when converting a single row - causing even further slowdown due to redundant copying. 

I've created a proposal for removing the deepcopy operation. Will reference relevant PR.

Pull request description:
feat: preserve unknown fields from the REST API representaton in `SchemaField`
Thank you for opening a Pull Request! Before submitting your PR, there are a few things you can do to make sure it goes smoothly:
- [ ] Make sure to open an issue as a [bug/issue](https://github.com/googleapis/python-bigquery/issues/new/choose) before writing your code!  That way we can discuss the change, evaluate designs, and agree on the general idea
- [ ] Ensure the tests and linter pass
- [ ] Code coverage does not decrease (if any source code was changed)
- [ ] Appropriate docs were updated (if necessary)

Towards simplifying https://github.com/googleapis/python-bigquery/pull/2081
Fixes #6 even more than it already was by avoiding even more copy operations.
🦕


Patch:
diff --git a/google/cloud/bigquery/schema.py b/google/cloud/bigquery/schema.py
index f5b03cbe..b062396c 100644
--- a/google/cloud/bigquery/schema.py
+++ b/google/cloud/bigquery/schema.py
@@ -16,8 +16,9 @@
 
 import collections
 import enum
-from typing import Any, Dict, Iterable, Optional, Union, cast
+from typing import Any, cast, Dict, Iterable, Optional, Union
 
+from google.cloud.bigquery import _helpers
 from google.cloud.bigquery import standard_sql
 from google.cloud.bigquery.enums import StandardSqlTypeNames
 
@@ -203,15 +204,8 @@ class SchemaField(object):
             self._properties["rangeElementType"] = {"type": range_element_type}
         if isinstance(range_element_type, FieldElementType):
             self._properties["rangeElementType"] = range_element_type.to_api_repr()
-
-        self._fields = tuple(fields)
-
-    @staticmethod
-    def __get_int(api_repr, name):
-        v = api_repr.get(name, _DEFAULT_VALUE)
-        if v is not _DEFAULT_VALUE:
-            v = int(v)
-        return v
+        if fields:  # Don't set the property if it's not set.
+            self._properties["fields"] = [field.to_api_repr() for field in fields]
 
     @classmethod
     def from_api_repr(cls, api_repr: dict) -> "SchemaField":
@@ -225,43 +219,19 @@ class SchemaField(object):
         Returns:
             google.cloud.bigquery.schema.SchemaField: The ``SchemaField`` object.
         """
-        field_type = api_repr["type"].upper()
-
-        # Handle optional properties with default values
-        mode = api_repr.get("mode", "NULLABLE")
-        description = api_repr.get("description", _DEFAULT_VALUE)
-        fields = api_repr.get("fields", ())
-        policy_tags = api_repr.get("policyTags", _DEFAULT_VALUE)
+        placeholder = cls("this_will_be_replaced", "PLACEHOLDER")
 
-        default_value_expression = api_repr.get("defaultValueExpression", None)
+        # Note: we don't make a copy of api_repr because this can cause
+        # unnecessary slowdowns, especially on deeply nested STRUCT / RECORD
+        # fields. See https://github.com/googleapis/python-bigquery/issues/6
+        placeholder._properties = api_repr
 
-        if policy_tags is not None and policy_tags is not _DEFAULT_VALUE:
-            policy_tags = PolicyTagList.from_api_repr(policy_tags)
-
-        if api_repr.get("rangeElementType"):
-            range_element_type = cast(dict, api_repr.get("rangeElementType"))
-            element_type = range_element_type.get("type")
-        else:
-            element_type = None
-
-        return cls(
-            field_type=field_type,
-            fields=[cls.from_api_repr(f) for f in fields],
-            mode=mode.upper(),
-            default_value_expression=default_value_expression,
-            description=description,
-            name=api_repr["name"],
-            policy_tags=policy_tags,
-            precision=cls.__get_int(api_repr, "precision"),
-            scale=cls.__get_int(api_repr, "scale"),
-            max_length=cls.__get_int(api_repr, "maxLength"),
-            range_element_type=element_type,
-        )
+        return placeholder
 
     @property
     def name(self):
         """str: The name of the field."""
-        return self._properties["name"]
+        return self._properties.get("name", "")
 
     @property
     def field_type(self):
@@ -270,7 +240,10 @@ class SchemaField(object):
         See:
         https://cloud.google.com/bigquery/docs/reference/rest/v2/tables#TableFieldSchema.FIELDS.type
         """
-        return self._properties["type"]
+        type_ = self._properties.get("type")
+        if type_ is None:  # Shouldn't happen, but some unit tests do this.
+            return None
+        return cast(str, type_).upper()
 
     @property
     def mode(self):
@@ -279,7 +252,7 @@ class SchemaField(object):
         See:
         https://cloud.google.com/bigquery/docs/reference/rest/v2/tables#TableFieldSchema.FIELDS.mode
         """
-        return self._properties.get("mode")
+        return cast(str, self._properties.get("mode", "NULLABLE")).upper()
 
     @property
     def is_nullable(self):
@@ -299,17 +272,17 @@ class SchemaField(object):
     @property
     def precision(self):
         """Optional[int]: Precision (number of digits) for the NUMERIC field."""
-        return self._properties.get("precision")
+        return _helpers._int_or_none(self._properties.get("precision"))
 
     @property
     def scale(self):
         """Optional[int]: Scale (digits after decimal) for the NUMERIC field."""
-        return self._properties.get("scale")
+        return _helpers._int_or_none(self._properties.get("scale"))
 
     @property
     def max_length(self):
         """Optional[int]: Maximum length for the STRING or BYTES field."""
-        return self._properties.get("maxLength")
+        return _helpers._int_or_none(self._properties.get("maxLength"))
 
     @property
     def range_element_type(self):
@@ -329,7 +302,7 @@ class SchemaField(object):
 
         Must be empty unset if ``field_type`` is not 'RECORD'.
         """
-        return self._fields
+        return tuple(_to_schema_fields(self._properties.get("fields", [])))
 
     @property
     def policy_tags(self):
@@ -345,15 +318,10 @@ class SchemaField(object):
         Returns:
             Dict: A dictionary representing the SchemaField in a serialized form.
         """
-        answer = self._properties.copy()
-
-        # If this is a RECORD type, then sub-fields are also included,
-        # add this to the serialized representation.
-        if self.field_type.upper() in _STRUCT_TYPES:
-            answer["fields"] = [f.to_api_repr() for f in self.fields]
-
-        # Done; return the serialized dictionary.
-        return answer
+        # Note: we don't make a copy of _properties because this can cause
+        # unnecessary slowdowns, especially on deeply nested STRUCT / RECORD
+        # fields. See https://github.com/googleapis/python-bigquery/issues/6
+        return self._properties
 
     def _key(self):
         """A tuple key that uniquely describes this field.
@@ -389,7 +357,7 @@ class SchemaField(object):
             self.mode.upper(),  # pytype: disable=attribute-error
             self.default_value_expression,
             self.description,
-            self._fields,
+            self.fields,
             policy_tags,
         )
 


Test patch:
diff --git a/tests/unit/job/test_load_config.py b/tests/unit/job/test_load_config.py
index becf3e95..3a681c47 100644
--- a/tests/unit/job/test_load_config.py
+++ b/tests/unit/job/test_load_config.py
@@ -12,6 +12,7 @@
 # See the License for the specific language governing permissions and
 # limitations under the License.
 
+import copy
 import warnings
 
 import pytest
@@ -571,16 +572,34 @@ class TestLoadJobConfig(_Base):
             config._properties["load"]["schema"], {"fields": [full_name_repr, age_repr]}
         )
 
-    def test_schema_setter_invalid_mappings_list(self):
+    def test_schema_setter_allows_unknown_properties(self):
         config = self._get_target_class()()
 
         schema = [
-            {"name": "full_name", "type": "STRING", "mode": "REQUIRED"},
-            {"name": "age", "typeoo": "INTEGER", "mode": "REQUIRED"},
+            {
+                "name": "full_name",
+                "type": "STRING",
+                "mode": "REQUIRED",
+                "someNewProperty": "test-value",
+            },
+            {
+                "name": "age",
+                # Note: This type should be included, too. Avoid client-side
+                # validation, as it could prevent backwards-compatible
+                # evolution of the server-side behavior.
+                "typo": "INTEGER",
+                "mode": "REQUIRED",
+                "anotherNewProperty": "another-test",
+            },
         ]
 
-        with self.assertRaises(Exception):
-            config.schema = schema
+        # Make sure the setter doesn't mutate schema.
+        expected_schema = copy.deepcopy(schema)
+
+        config.schema = schema
+
+        # _properties should include all fields, including unknown ones.
+        assert config._properties["load"]["schema"]["fields"] == expected_schema
 
     def test_schema_setter_unsetting_schema(self):
         from google.cloud.bigquery.schema import SchemaField
diff --git a/tests/unit/test_schema.py b/tests/unit/test_schema.py
index b17cd028..4b0b2815 100644
--- a/tests/unit/test_schema.py
+++ b/tests/unit/test_schema.py
@@ -12,14 +12,16 @@
 # See the License for the specific language governing permissions and
 # limitations under the License.
 
-from google.cloud import bigquery
-from google.cloud.bigquery.standard_sql import StandardSqlStructType
-from google.cloud.bigquery.schema import PolicyTagList
+import copy
 import unittest
 from unittest import mock
 
 import pytest
 
+from google.cloud import bigquery
+from google.cloud.bigquery.standard_sql import StandardSqlStructType
+from google.cloud.bigquery.schema import PolicyTagList
+
 
 class TestSchemaField(unittest.TestCase):
     @staticmethod
@@ -821,13 +823,32 @@ class Test_to_schema_fields(unittest.TestCase):
         result = self._call_fut(schema)
         self.assertEqual(result, schema)
 
-    def test_invalid_mapping_representation(self):
+    def test_unknown_properties(self):
         schema = [
-            {"name": "full_name", "type": "STRING", "mode": "REQUIRED"},
-            {"name": "address", "typeooo": "STRING", "mode": "REQUIRED"},
+            {
+                "name": "full_name",
+                "type": "STRING",
+                "mode": "REQUIRED",
+                "someNewProperty": "test-value",
+            },
+            {
+                "name": "age",
+                # Note: This type should be included, too. Avoid client-side
+                # validation, as it could prevent backwards-compatible
+                # evolution of the server-side behavior.
+                "typo": "INTEGER",
+                "mode": "REQUIRED",
+                "anotherNewProperty": "another-test",
+            },
         ]
-        with self.assertRaises(Exception):
-            self._call_fut(schema)
+
+        # Make sure the setter doesn't mutate schema.
+        expected_schema = copy.deepcopy(schema)
+
+        result = self._call_fut(schema)
+
+        for api_repr, field in zip(expected_schema, result):
+            assert field.to_api_repr() == api_repr
 
     def test_valid_mapping_representation(self):
         from google.cloud.bigquery.schema import SchemaField
diff --git a/tests/unit/test_table.py b/tests/unit/test_table.py
index 3824da22..e9d461e9 100644
--- a/tests/unit/test_table.py
+++ b/tests/unit/test_table.py
@@ -12,6 +12,7 @@
 # See the License for the specific language governing permissions and
 # limitations under the License.
 
+import copy
 import datetime
 import logging
 import re
@@ -711,14 +712,35 @@ class TestTable(unittest.TestCase, _SchemaBase):
         table.schema = [full_name, age]
         self.assertEqual(table.schema, [full_name, age])
 
-    def test_schema_setter_invalid_mapping_representation(self):
+    def test_schema_setter_allows_unknown_properties(self):
         dataset = DatasetReference(self.PROJECT, self.DS_ID)
         table_ref = dataset.table(self.TABLE_NAME)
         table = self._make_one(table_ref)
-        full_name = {"name": "full_name", "type": "STRING", "mode": "REQUIRED"}
-        invalid_field = {"name": "full_name", "typeooo": "STRING", "mode": "REQUIRED"}
-        with self.assertRaises(Exception):
-            table.schema = [full_name, invalid_field]
+        schema = [
+            {
+                "name": "full_name",
+                "type": "STRING",
+                "mode": "REQUIRED",
+                "someNewProperty": "test-value",
+            },
+            {
+                "name": "age",
+                # Note: This type should be included, too. Avoid client-side
+                # validation, as it could prevent backwards-compatible
+                # evolution of the server-side behavior.
+                "typo": "INTEGER",
+                "mode": "REQUIRED",
+                "anotherNewProperty": "another-test",
+            },
+        ]
+
+        # Make sure the setter doesn't mutate schema.
+        expected_schema = copy.deepcopy(schema)
+
+        table.schema = schema
+
+        # _properties should include all fields, including unknown ones.
+        assert table._properties["schema"]["fields"] == expected_schema
 
     def test_schema_setter_valid_mapping_representation(self):
         from google.cloud.bigquery.schema import SchemaField