♻️ Refactor generate select template to isolate templated code to the minimum

pyproject.toml

@@ -90,7 +90,7 @@ exclude_lines = [
 strict = true
 
 [[tool.mypy.overrides]]
-module = "sqlmodel.sql.expression"
+module = "sqlmodel.sql._expression_select_gen"
 warn_unused_ignores = false
 
 [[tool.mypy.overrides]]

scripts/generate_select.py

@@ -7,8 +7,10 @@
 from jinja2 import Template
 from pydantic import BaseModel
 
-template_path = Path(__file__).parent.parent / "sqlmodel/sql/expression.py.jinja2"
-destiny_path = Path(__file__).parent.parent / "sqlmodel/sql/expression.py"
+template_path = (
+    Path(__file__).parent.parent / "sqlmodel/sql/_expression_select_gen.py.jinja2"
+)
+destiny_path = Path(__file__).parent.parent / "sqlmodel/sql/_expression_select_gen.py"
 
 
 number_of_types = 4
@@ -48,7 +50,7 @@ class Arg(BaseModel):
 
 result = (
     "# WARNING: do not modify this code, it is generated by "
-    "expression.py.jinja2\n\n" + result
+    "_expression_select_gen.py.jinja2\n\n" + result
 )
 
 result = black.format_str(result, mode=black.Mode())

sqlmodel/sql/_expression_select_cls.py

@@ -0,0 +1,43 @@
+from typing import (
+    Tuple,
+    TypeVar,
+    Union,
+)
+
+from sqlalchemy.sql._typing import (
+    _ColumnExpressionArgument,
+)
+from sqlalchemy.sql.expression import Select as _Select
+from typing_extensions import Self
+
+_T = TypeVar("_T")
+
+
+# Separate this class in SelectBase, Select, and SelectOfScalar so that they can share
+# where and having without having type overlap incompatibility in session.exec().
+class SelectBase(_Select[Tuple[_T]]):
+    inherit_cache = True
+
+    def where(self, *whereclause: Union[_ColumnExpressionArgument[bool], bool]) -> Self:
+        """Return a new `Select` construct with the given expression added to
+        its `WHERE` clause, joined to the existing clause via `AND`, if any.
+        """
+        return super().where(*whereclause)  # type: ignore[arg-type]
+
+    def having(self, *having: Union[_ColumnExpressionArgument[bool], bool]) -> Self:
+        """Return a new `Select` construct with the given expression added to
+        its `HAVING` clause, joined to the existing clause via `AND`, if any.
+        """
+        return super().having(*having)  # type: ignore[arg-type]
+
+
+class Select(SelectBase[_T]):
+    inherit_cache = True
+
+
+# This is not comparable to sqlalchemy.sql.selectable.ScalarSelect, that has a different
+# purpose. This is the same as a normal SQLAlchemy Select class where there's only one
+# entity, so the result will be converted to a scalar by default. This way writing
+# for loops on the results will feel natural.
+class SelectOfScalar(SelectBase[_T]):
+    inherit_cache = True