Improve error in dataclasses with table

Added a better error when trying to map as dataclass a class while also
manually providing the ``__table__`` attribute.
This usage is currently not supported.

Fixes: #11973
Change-Id: I54c721b3f7447b2f062fa0cfb53b6a88c381df42

diff --git a/doc/build/changelog/unreleased_20/11973.rst b/doc/build/changelog/unreleased_20/11973.rst
new file mode 100644 (file)
index 0000000..bad0f22
--- /dev/null
+++ b/doc/build/changelog/unreleased_20/11973.rst
@@ -0,0 +1,7 @@
+.. change::
+    :tags: orm, bug
+    :tickets: 11973
+
+    Improved the error message emitted when trying to map as dataclass a class
+    while also manually providing the ``__table__`` attribute.
+    This usage is currently not supported.

diff --git a/lib/sqlalchemy/orm/decl_base.py b/lib/sqlalchemy/orm/decl_base.py
index 271c61a8b6ef3551decbf937496ac3779755f5e8..8b42a32dfb08ce956c38bde5aefb201d7a6863e5 100644 (file)
--- a/lib/sqlalchemy/orm/decl_base.py
+++ b/lib/sqlalchemy/orm/decl_base.py
@@ -1067,6 +1067,16 @@ class _ClassScanMapperConfig(_MapperConfig):
                 "'@registry.mapped_as_dataclass'"
             )
 
+        # can't create a dataclass if __table__ is already there. This would
+        # fail an assertion when calling _get_arguments_for_make_dataclass:
+        # assert False, "Mapped[] received without a mapping declaration"
+        if "__table__" in self.cls.__dict__:
+            raise exc.InvalidRequestError(
+                f"Class {self.cls} already defines a '__table__'. "
+                "ORM Annotated Dataclasses do not support a pre-existing "
+                "'__table__' element"
+            )
+
         warn_for_non_dc_attrs = collections.defaultdict(list)
 
         def _allow_dataclass_field(

diff --git a/test/orm/declarative/test_dc_transforms.py b/test/orm/declarative/test_dc_transforms.py
index 8408f696176f715f49ae3eb1c257493e30c4fad5..4c4f158513fa964db7f0a43a8aa6a8a70956e446 100644 (file)
--- a/test/orm/declarative/test_dc_transforms.py
+++ b/test/orm/declarative/test_dc_transforms.py
@@ -27,6 +27,7 @@ from sqlalchemy import Integer
 from sqlalchemy import JSON
 from sqlalchemy import select
 from sqlalchemy import String
+from sqlalchemy import Table
 from sqlalchemy import testing
 from sqlalchemy.ext.associationproxy import association_proxy
 from sqlalchemy.orm import column_property
@@ -742,6 +743,21 @@ class DCTransformsTest(AssertsCompiledSQL, fixtures.TestBase):
             class Foo(Mixin):
                 bar_value: Mapped[float] = mapped_column(default=78)
 
+    def test_MappedAsDataclass_table_provided(self, registry):
+        """test #11973"""
+
+        with expect_raises_message(
+            exc.InvalidRequestError,
+            "Class .*Foo.* already defines a '__table__'. "
+            "ORM Annotated Dataclasses do not support a pre-existing "
+            "'__table__' element",
+        ):
+
+            @registry.mapped_as_dataclass
+            class Foo:
+                __table__ = Table("foo", registry.metadata)
+                foo: Mapped[float]
+
     def test_dataclass_exception_wrapped(self, dc_decl_base):
         with expect_raises_message(
             exc.InvalidRequestError,