Fix remote_side for composite self-referential FK targeting a UNIQUE constraint (#484)

CHANGES.rst

@@ -1,6 +1,13 @@
 Version history
 ===============
 
+**UNRELEASED**
+
+- Fixed ``remote_side`` in a self-referential relationship pointing at the primary key
+  when the foreign key targets other columns (such as a ``UNIQUE`` constraint), which
+  made mapper configuration fail with ``ArgumentError``
+  (`#484 <https://github.com/agronholm/sqlacodegen/issues/484>`_; PR by @NixBiks)
+
 **4.0.4**
 
 - Added autoincrement to primary key columns to prevent missing field errors.

src/sqlacodegen/generators.py

@@ -1271,8 +1271,8 @@ def generate_relationships(
                 # For self referential relationships, remote_side needs to be set
                 if source is target:
                     relationship.remote_side = [
-                        source.get_column_attribute(col.name)
-                        for col in constraint.referred_table.primary_key
+                        source.get_column_attribute(element.column.name)
+                        for element in constraint.elements
                     ]
 
                 # If the two tables share more than one foreign key constraint,

tests/test_generator_declarative.py

@@ -483,6 +483,56 @@ class SimpleItems(Base):
     )
 
 
+def test_onetomany_selfref_composite_unique_target(generator: CodeGenerator) -> None:
+    Table(
+        "simple_items",
+        generator.metadata,
+        Column("id", INTEGER, primary_key=True),
+        Column("scheme", VARCHAR, nullable=False),
+        Column("code", VARCHAR, nullable=False),
+        Column("parent_scheme", VARCHAR),
+        Column("parent_code", VARCHAR),
+        UniqueConstraint("scheme", "code"),
+        ForeignKeyConstraint(
+            ["parent_scheme", "parent_code"],
+            ["simple_items.scheme", "simple_items.code"],
+        ),
+    )
+
+    validate_code(
+        generator.generate(),
+        """\
+from typing import Optional
+
+from sqlalchemy import ForeignKeyConstraint, Integer, String, UniqueConstraint
+from sqlalchemy.orm import DeclarativeBase, Mapped, mapped_column, relationship
+
+class Base(DeclarativeBase):
+    pass
+
+
+class SimpleItems(Base):
+    __tablename__ = 'simple_items'
+    __table_args__ = (
+        ForeignKeyConstraint(['parent_scheme', 'parent_code'], \
+['simple_items.scheme', 'simple_items.code']),
+        UniqueConstraint('scheme', 'code')
+    )
+
+    id: Mapped[int] = mapped_column(Integer, primary_key=True)
+    scheme: Mapped[str] = mapped_column(String, nullable=False)
+    code: Mapped[str] = mapped_column(String, nullable=False)
+    parent_scheme: Mapped[Optional[str]] = mapped_column(String)
+    parent_code: Mapped[Optional[str]] = mapped_column(String)
+
+    simple_items: Mapped[Optional['SimpleItems']] = relationship('SimpleItems', \
+remote_side=[scheme, code], back_populates='simple_items_reverse')
+    simple_items_reverse: Mapped[list['SimpleItems']] = relationship('SimpleItems', \
+remote_side=[parent_scheme, parent_code], back_populates='simple_items')
+""",
+    )
+
+
 def test_onetomany_composite(generator: CodeGenerator) -> None:
     Table(
         "simple_items",