Improve Identity server_default rendering for Decimal values (#470)

* Enhance Identity column support for Decimal values in SQLAlchemy

* Improve Identity server defaults rendering to support Decimal values

* [pre-commit.ci] auto fixes from pre-commit.com hooks

for more information, see https://pre-commit.ci

* Fix Identity server defaults to cast Decimal values to int

* Improve rendering of Identity server defaults to explicitly handle Decimal values

* Update src/sqlacodegen/generators.py

Co-authored-by: Alex Grönholm <alex.gronholm@nextday.fi>

* Refactor Identity server default handling to simplify Decimal value serialization

* Refactor Identity handling to improve Decimal value serialization

* Add test for Identity column with Decimal values in generator

* Add test for Identity column with Decimal values

* Fix Identity column Decimal value assignment using setattr

* Add test for Identity column with Decimal values serialization

* Refactor test for Identity column to directly assign Decimal values

---------

Co-authored-by: pre-commit-ci[bot] <66853113+pre-commit-ci[bot]@users.noreply.github.com>
Co-authored-by: Alex Grönholm <alex.gronholm@nextday.fi>

Author: 3 people

CHANGES.rst

@@ -1,6 +1,12 @@
 Version history
 ===============
 
+**UNRELEASED**
+
+- Improved rendering of ``Identity`` server defaults by explicitly rendering
+  non-default parameters; ``Decimal`` values (as returned by some databases) are
+  now cast to ``int`` (PR by @NotCarlosSerrano)
+
 **4.0.2**
 
 - Fixed rendering of inherited keyword arguments for dialect-specific types that use

src/sqlacodegen/generators.py

@@ -7,6 +7,7 @@
 from collections import defaultdict
 from collections.abc import Collection, Iterable, Mapping, Sequence
 from dataclasses import dataclass
+from decimal import Decimal
 from importlib import import_module
 from inspect import Parameter
 from itertools import count
@@ -521,7 +522,29 @@ def render_column(
                 render_callable("Computed", repr(expression), kwargs=computed_kwargs)
             )
         elif isinstance(column.server_default, Identity):
-            args.append(repr(column.server_default))
+            identity = column.server_default
+            identity_kwargs: dict[str, Any] = {}
+
+            for name, param in inspect.signature(Identity).parameters.items():
+                if name == "self" or param.kind in (
+                    Parameter.VAR_POSITIONAL,
+                    Parameter.VAR_KEYWORD,
+                ):
+                    continue
+
+                value = getattr(identity, name, None)
+                if value is None:
+                    continue
+
+                if isinstance(value, Decimal):
+                    value = int(value)
+
+                if param.default is not Parameter.empty and value == param.default:
+                    continue
+
+                identity_kwargs[name] = value
+
+            args.append(render_callable("Identity", kwargs=identity_kwargs))
         elif column.server_default:
             kwargs["server_default"] = repr(column.server_default)
 

tests/test_generator_tables.py

@@ -1,5 +1,6 @@
 from __future__ import annotations
 
+from decimal import Decimal
 from textwrap import dedent
 
 import pytest
@@ -1217,6 +1218,40 @@ def test_identity_column(generator: CodeGenerator) -> None:
     )
 
 
+def test_identity_column_decimal_values(generator: CodeGenerator) -> None:
+    # MSSQL reflects Identity column parameters (start, increment) as Decimal
+    # values instead of integers. This test ensures those are serialized correctly.
+    identity = Identity(start=1, increment=2)
+    # Simulate database reflection returning Decimal values (as MSSQL does)
+    identity.start = Decimal("1")  # type: ignore[assignment]
+    identity.increment = Decimal("2")  # type: ignore[assignment]
+    Table(
+        "simple_items",
+        generator.metadata,
+        Column(
+            "id",
+            INTEGER,
+            primary_key=True,
+            server_default=identity,
+        ),
+    )
+
+    validate_code(
+        generator.generate(),
+        """\
+        from sqlalchemy import Column, Identity, Integer, MetaData, Table
+
+        metadata = MetaData()
+
+
+        t_simple_items = Table(
+            'simple_items', metadata,
+            Column('id', Integer, Identity(start=1, increment=2), primary_key=True)
+        )
+        """,
+    )
+
+
 def test_multiline_column_comment(generator: CodeGenerator) -> None:
     Table(
         "simple_items",