Add option for deterministic defaults (#18)

Author: giograno

src/py_avro_schema/_schemas.py

@@ -147,6 +147,10 @@ class Option(enum.Flag):
     #: Add an __id field to records to track the id of mutable objects
     ADD_REFERENCE_ID = enum.auto()
 
+    # Use deterministic default values for volatile types like datetime or strings like UUIDs. Non-deterministic
+    # factories might a problem when comparing schemas, as they change every time a schema is generated by definition.
+    DETERMINISTIC_DEFAULTS = enum.auto()
+
 
 JSON_OPTIONS = [opt for opt in Option if opt.name and opt.name.startswith("JSON_")]
 
@@ -221,6 +225,7 @@ def _schema_obj(py_type: Type, namespace: Optional[str] = None, options: Option
 
 # See https://avro.apache.org/docs/1.11.1/specification/#names
 _AVRO_NAME_PATTERN = re.compile(r"^[A-Za-z]([A-Za-z0-9_])*$")
+_UUID_PATTERN = re.compile(r"^[0-9a-f]{8}(?:-[0-9a-f]{4}-[0-9a-f]{4}-[0-9a-f]{4}-[0-9a-f]{12})?$", re.IGNORECASE)
 
 
 def validate_name(value: str) -> str:
@@ -487,6 +492,8 @@ def data(self, names: NamesType) -> JSONObj:
 
     def make_default(self, py_default: datetime.date) -> int:
         """Return an Avro schema compliant default value for a given Python value"""
+        if Option.DETERMINISTIC_DEFAULTS in self.options:
+            return 0
         return (py_default - datetime.date(1970, 1, 1)).days
 
 
@@ -510,6 +517,8 @@ def data(self, names: NamesType) -> JSONObj:
 
     def make_default(self, py_default: datetime.time) -> int:
         """Return an Avro schema compliant default value for a given Python value"""
+        if Option.DETERMINISTIC_DEFAULTS in self.options:
+            return 0
         # Force UTC as we're concerned only about time diffs
         dt1 = datetime.datetime(1, 1, 1, tzinfo=datetime.timezone.utc)
         dt2 = datetime.datetime.combine(datetime.datetime(1, 1, 1), py_default, tzinfo=datetime.timezone.utc)
@@ -532,6 +541,8 @@ def data(self, names: NamesType) -> JSONObj:
 
     def make_default(self, py_default: datetime.datetime) -> int:
         """Return an Avro schema compliant default value for a given Python value"""
+        if Option.DETERMINISTIC_DEFAULTS in self.options:
+            return 0
         if not py_default.tzinfo:
             raise TypeError(f"Default {py_default!r} must be timezone-aware")
         return int((py_default - datetime.datetime.fromtimestamp(0, tz=datetime.timezone.utc)).total_seconds() * 1e6)
@@ -1079,7 +1090,18 @@ def data(self, names: NamesType) -> JSONObj:
         if self.aliases:
             field_data["aliases"] = sorted(self.aliases)
         if self.default != dataclasses.MISSING:
-            field_data["default"] = self.schema.make_default(self.default)
+            default_value = self.schema.make_default(self.default)
+
+            # When a field is a string, but it's default value produces a UUID-like, we do not pass through the UUID
+            # schema (which already sets an empty default). We need to catch here the strings that look like a UUID
+            # and set a deterministic default.
+            if (
+                Option.DETERMINISTIC_DEFAULTS in self.options
+                and isinstance(default_value, str)
+                and _UUID_PATTERN.match(default_value)
+            ):
+                default_value = ""
+            field_data["default"] = default_value
         if self.docs and Option.NO_DOC not in self.options:
             field_data["doc"] = self.docs
         return field_data

tests/test_dataclass.py

@@ -887,3 +887,57 @@ class PyType:
         ],
     }
     assert_schema(PyType, expected, options=Option.ADD_REFERENCE_ID)
+
+
+def test_deterministic_defaults_datetime():
+    @dataclasses.dataclass
+    class PyType:
+        field_a: datetime.datetime = dataclasses.field(
+            default_factory=lambda: datetime.datetime.now(tz=datetime.timezone.utc)
+        )
+
+    expected = {
+        "type": "record",
+        "name": "PyType",
+        "fields": [
+            {
+                "name": "field_a",
+                "type": {"type": "long", "logicalType": "timestamp-micros"},
+                "default": 0,
+            }
+        ],
+    }
+    assert_schema(PyType, expected, options=pas.Option.DETERMINISTIC_DEFAULTS)
+
+
+def test_deterministic_defaults_uuid_str():
+    import uuid
+
+    def short_uid() -> str:
+        return str(uuid.uuid4())[0:8]
+
+    def long_uid() -> str:
+        return str(uuid.uuid4())
+
+    @dataclasses.dataclass
+    class PyType:
+        _long_uid: str = dataclasses.field(default_factory=long_uid)
+        _short_uid: str = dataclasses.field(default_factory=short_uid)
+
+    expected = {
+        "type": "record",
+        "name": "PyType",
+        "fields": [
+            {
+                "name": "_long_uid",
+                "type": "string",
+                "default": "",
+            },
+            {
+                "name": "_short_uid",
+                "type": "string",
+                "default": "",
+            },
+        ],
+    }
+    assert_schema(PyType, expected, options=pas.Option.DETERMINISTIC_DEFAULTS)