Add support to secondary tables relationships

src/strawberry_sqlalchemy_mapper/exc.py

@@ -36,3 +36,11 @@ def __init__(self, model):
             f"Model `{model}` is not polymorphic or is not the base model of its "
             + "inheritance chain, and thus cannot be used as an interface."
         )
+
+
+class InvalidLocalRemotePairs(Exception):
+    def __init__(self, relationship_name):
+        super().__init__(
+            f"The `local_remote_pairs` for the relationship `{relationship_name}` is invalid or missing. "
+            + "This is likely an issue with the library. Please report this error to the maintainers."
+        )

src/strawberry_sqlalchemy_mapper/loader.py

@@ -11,6 +11,7 @@
     Tuple,
     Union,
 )
+from strawberry_sqlalchemy_mapper.exc import InvalidLocalRemotePairs
 
 from sqlalchemy import select, tuple_
 from sqlalchemy.engine.base import Connection
@@ -45,12 +46,16 @@ def __init__(
                 "One of bind or async_bind_factory must be set for loader to function properly."
             )
 
-    async def _scalars_all(self, *args, **kwargs):
+    async def _scalars_all(self, *args, disabled_optimization_to_secondary_tables=False, **kwargs):
         if self._async_bind_factory:
             async with self._async_bind_factory() as bind:
+                if disabled_optimization_to_secondary_tables is True:
+                    return (await bind.execute(*args, **kwargs)).all()
                 return (await bind.scalars(*args, **kwargs)).all()
         else:
             assert self._bind is not None
+            if disabled_optimization_to_secondary_tables is True:
+                return self._bind.execute(*args, **kwargs).all()
             return self._bind.scalars(*args, **kwargs).all()
 
     def loader_for(self, relationship: RelationshipProperty) -> DataLoader:
@@ -63,14 +68,63 @@ def loader_for(self, relationship: RelationshipProperty) -> DataLoader:
             related_model = relationship.entity.entity
 
             async def load_fn(keys: List[Tuple]) -> List[Any]:
-                query = select(related_model).filter(
-                    tuple_(
-                        *[remote for _, remote in relationship.local_remote_pairs or []]
-                    ).in_(keys)
-                )
+                if relationship.secondary is None:
+                    query = select(related_model).filter(
+                        tuple_(
+                            *[remote for _, remote in relationship.local_remote_pairs or []]
+                        ).in_(keys)
+                    )
+                else:
+                    # Use another query when relationship uses a secondary table
+                    self_model = relationship.parent.entity
+
+                    if not relationship.local_remote_pairs:
+                        raise InvalidLocalRemotePairs(
+                            f"{related_model.__name__} -- {self_model.__name__}")
+
+                    self_model_key_label = str(
+                        relationship.local_remote_pairs[0][1].key)
+                    related_model_key_label = str(
+                        relationship.local_remote_pairs[1][1].key)
+
+                    self_model_key = str(
+                        relationship.local_remote_pairs[0][0].key)
+                    related_model_key = str(
+                        relationship.local_remote_pairs[1][0].key)
+
+                    remote_to_use = relationship.local_remote_pairs[0][1]
+                    query_keys = tuple([item[0] for item in keys])
+
+                    # This query returns rows in this format -> (self_model.key, related_model)
+                    query = (
+                        select(
+                            getattr(self_model, self_model_key).label(
+                                self_model_key_label),
+                            related_model
+                        )
+                        .join(
+                            relationship.secondary,
+                            getattr(relationship.secondary.c,
+                                    related_model_key_label) == getattr(related_model, related_model_key)
+                        )
+                        .join(
+                            self_model,
+                            getattr(relationship.secondary.c,
+                                    self_model_key_label) == getattr(self_model, self_model_key)
+                        )
+                        .filter(
+                            remote_to_use.in_(query_keys)
+                        )
+                    )
+
                 if relationship.order_by:
                     query = query.order_by(*relationship.order_by)
-                rows = await self._scalars_all(query)
+
+                if relationship.secondary is not None:
+                    # We need to retrieve values from both the self_model and related_model. To achieve this, we must disable the default SQLAlchemy optimization that returns only related_model values. This is necessary because we use the keys variable to match both related_model and self_model.
+                    rows = await self._scalars_all(query, disabled_optimization_to_secondary_tables=True)
+                else:
+                    rows = await self._scalars_all(query)
 
                 def group_by_remote_key(row: Any) -> Tuple:
                     return tuple(
@@ -82,8 +136,13 @@ def group_by_remote_key(row: Any) -> Tuple:
                     )
 
                 grouped_keys: Mapping[Tuple, List[Any]] = defaultdict(list)
-                for row in rows:
-                    grouped_keys[group_by_remote_key(row)].append(row)
+                if relationship.secondary is None:
+                    for row in rows:
+                        grouped_keys[group_by_remote_key(row)].append(row)
+                else:
+                    for row in rows:
+                        grouped_keys[(row[0],)].append(row[1])
+
                 if relationship.uselist:
                     return [grouped_keys[key] for key in keys]
                 else:

src/strawberry_sqlalchemy_mapper/mapper.py

@@ -82,6 +82,7 @@
 from strawberry_sqlalchemy_mapper.exc import (
     HybridPropertyNotAnnotated,
     InterfaceModelNotPolymorphic,
+    InvalidLocalRemotePairs,
     UnsupportedAssociationProxyTarget,
     UnsupportedColumnType,
     UnsupportedDescriptorType,
@@ -154,7 +155,8 @@ def from_type(cls, type_: type, *, strict: Literal[True]) -> Self: ...
 
     @overload
     @classmethod
-    def from_type(cls, type_: type, *, strict: bool = False) -> Optional[Self]: ...
+    def from_type(cls, type_: type, *,
+                  strict: bool = False) -> Optional[Self]: ...
 
     @classmethod
     def from_type(
@@ -165,7 +167,8 @@ def from_type(
     ) -> Optional[Self]:
         definition = getattr(type_, cls.TYPE_KEY_NAME, None)
         if strict and definition is None:
-            raise TypeError(f"{type_!r} does not have a StrawberrySQLAlchemyType in it")
+            raise TypeError(
+                f"{type_!r} does not have a StrawberrySQLAlchemyType in it")
         return definition
 
 
@@ -228,11 +231,12 @@ class StrawberrySQLAlchemyMapper(Generic[BaseModelType]):
 
     def __init__(
         self,
-        model_to_type_name: Optional[Callable[[Type[BaseModelType]], str]] = None,
-        model_to_interface_name: Optional[Callable[[Type[BaseModelType]], str]] = None,
-        extra_sqlalchemy_type_to_strawberry_type_map: Optional[
-            Mapping[Type[TypeEngine], Type[Any]]
-        ] = None,
+        model_to_type_name: Optional[Callable[[
+            Type[BaseModelType]], str]] = None,
+        model_to_interface_name: Optional[Callable[[
+            Type[BaseModelType]], str]] = None,
+        extra_sqlalchemy_type_to_strawberry_type_map: Optional[Mapping[Type[TypeEngine], Type[Any]]
+                                                               ] = None,
     ) -> None:
         if model_to_type_name is None:
             model_to_type_name = self._default_model_to_type_name
@@ -295,7 +299,8 @@ def _edge_type_for(self, type_name: str) -> Type[Any]:
         """
         edge_name = f"{type_name}Edge"
         if edge_name not in self.edge_types:
-            lazy_type = StrawberrySQLAlchemyLazy(type_name=type_name, mapper=self)
+            lazy_type = StrawberrySQLAlchemyLazy(
+                type_name=type_name, mapper=self)
             self.edge_types[edge_name] = edge_type = strawberry.type(
                 dataclasses.make_dataclass(
                     edge_name,
@@ -314,14 +319,15 @@ def _connection_type_for(self, type_name: str) -> Type[Any]:
         connection_name = f"{type_name}Connection"
         if connection_name not in self.connection_types:
             edge_type = self._edge_type_for(type_name)
-            lazy_type = StrawberrySQLAlchemyLazy(type_name=type_name, mapper=self)
+            lazy_type = StrawberrySQLAlchemyLazy(
+                type_name=type_name, mapper=self)
             self.connection_types[connection_name] = connection_type = strawberry.type(
                 dataclasses.make_dataclass(
                     connection_name,
                     [
                         ("edges", List[edge_type]),  # type: ignore[valid-type]
                     ],
-                    bases=(relay.ListConnection[lazy_type],),  # type: ignore[valid-type]
+                    bases=(relay.ListConnection[lazy_type],), # type: ignore[valid-type]
                 )
             )
             setattr(connection_type, _GENERATED_FIELD_KEYS_KEY, ["edges"])
@@ -387,7 +393,7 @@ def _convert_relationship_to_strawberry_type(
         if relationship.uselist:
             # Use list if excluding relay pagination
             if use_list:
-                return List[ForwardRef(type_name)] # type: ignore
+                return List[ForwardRef(type_name)]  # type: ignore
 
             return self._connection_type_for(type_name)
         else:
@@ -451,7 +457,8 @@ def _get_association_proxy_annotation(
                     strawberry_type.__forward_arg__
                 )
             else:
-                strawberry_type = self._connection_type_for(strawberry_type.__name__)
+                strawberry_type = self._connection_type_for(
+                    strawberry_type.__name__)
         return strawberry_type
 
     def make_connection_wrapper_resolver(
@@ -500,13 +507,29 @@ async def resolve(self, info: Info):
             if relationship.key not in instance_state.unloaded:
                 related_objects = getattr(self, relationship.key)
             else:
-                relationship_key = tuple(
-                    [
-                        getattr(self, local.key)
-                        for local, _ in relationship.local_remote_pairs or []
-                        if local.key
-                    ]
-                )
+                if relationship.secondary is None:
+                    relationship_key = tuple(
+                        [
+                            getattr(self, local.key)
+                            for local, _ in relationship.local_remote_pairs or []
+                            if local.key
+                        ]
+                    )
+                else:
+                    # If has a secondary table, gets only the first ID as additional IDs require a separate query
+                    if not relationship.local_remote_pairs:
+                        raise InvalidLocalRemotePairs(
+                            f"{relationship.entity.entity.__name__} -- {relationship.parent.entity.__name__}")
+
+                    local_remote_pairs_secondary_table_local = relationship.local_remote_pairs[
+                        0][0]
+                    relationship_key = tuple(
+                        [
+                            getattr(
+                                self, str(local_remote_pairs_secondary_table_local.key)),
+                        ]
+                    )
+
                 if any(item is None for item in relationship_key):
                     if relationship.uselist:
                         return []
@@ -536,7 +559,8 @@ def connection_resolver_for(
         if relationship.uselist and not use_list:
             return self.make_connection_wrapper_resolver(
                 relationship_resolver,
-                self.model_to_type_or_interface_name(relationship.entity.entity),  # type: ignore[arg-type]
+                self.model_to_type_or_interface_name(
+                    relationship.entity.entity),  # type: ignore[arg-type]
             )
         else:
             return relationship_resolver
@@ -554,13 +578,15 @@ def association_proxy_resolver_for(
         Return an async field resolver for the given association proxy.
         """
         in_between_relationship = mapper.relationships[descriptor.target_collection]
-        in_between_resolver = self.relationship_resolver_for(in_between_relationship)
+        in_between_resolver = self.relationship_resolver_for(
+            in_between_relationship)
         in_between_mapper: Mapper = mapper.relationships[  # type: ignore[assignment]
             descriptor.target_collection
         ].entity
         assert descriptor.value_attr in in_between_mapper.relationships
         end_relationship = in_between_mapper.relationships[descriptor.value_attr]
-        end_relationship_resolver = self.relationship_resolver_for(end_relationship)
+        end_relationship_resolver = self.relationship_resolver_for(
+            end_relationship)
         end_type_name = self.model_to_type_or_interface_name(
             end_relationship.entity.entity  # type: ignore[arg-type]
         )
@@ -587,7 +613,8 @@ async def resolve(self, info: Info):
                     if outputs and isinstance(outputs[0], list):
                         outputs = list(chain.from_iterable(outputs))
                     else:
-                        outputs = [output for output in outputs if output is not None]
+                        outputs = [
+                            output for output in outputs if output is not None]
                 else:
                     outputs = await end_relationship_resolver(in_between_objects, info)
                 if not isinstance(outputs, collections.abc.Iterable):
@@ -683,7 +710,8 @@ def convert(type_: Any) -> Any:
                     setattr(type_, key, field(resolver=val))
                     generated_field_keys.append(key)
 
-            self._handle_columns(mapper, type_, excluded_keys, generated_field_keys)
+            self._handle_columns(
+                mapper, type_, excluded_keys, generated_field_keys)
             relationship: RelationshipProperty
             for key, relationship in mapper.relationships.items():
                 if (
@@ -805,7 +833,7 @@ def convert(type_: Any) -> Any:
                         setattr(
                             type_,
                             attr,
-                            types.MethodType(func, type_),  # type: ignore[arg-type]
+                            types.MethodType(func, type_), # type: ignore[arg-type]
                         )
 
                     # Adjust types that inherit from other types/interfaces that implement Node
@@ -818,7 +846,8 @@ def convert(type_: Any) -> Any:
                         setattr(
                             type_,
                             attr,
-                            types.MethodType(cast(classmethod, meth).__func__, type_),
+                            types.MethodType(
+                                cast(classmethod, meth).__func__, type_),
                         )
 
             # need to make fields that are already in the type
@@ -846,7 +875,8 @@ def convert(type_: Any) -> Any:
                     model=model,
                 ),
             )
-            setattr(mapped_type, _GENERATED_FIELD_KEYS_KEY, generated_field_keys)
+            setattr(mapped_type, _GENERATED_FIELD_KEYS_KEY,
+                    generated_field_keys)
             setattr(mapped_type, _ORIGINAL_TYPE_KEY, type_)
             return mapped_type
 
@@ -886,14 +916,16 @@ def _fix_annotation_namespaces(self) -> None:
             self.edge_types.values(),
             self.connection_types.values(),
         ):
-            strawberry_definition = get_object_definition(mapped_type, strict=True)
+            strawberry_definition = get_object_definition(
+                mapped_type, strict=True)
             for f in strawberry_definition.fields:
                 if f.name in getattr(mapped_type, _GENERATED_FIELD_KEYS_KEY):
                     namespace = {}
                     if hasattr(mapped_type, _ORIGINAL_TYPE_KEY):
                         namespace.update(
                             sys.modules[
-                                getattr(mapped_type, _ORIGINAL_TYPE_KEY).__module__
+                                getattr(mapped_type,
+                                        _ORIGINAL_TYPE_KEY).__module__
                             ].__dict__
                         )
                     namespace.update(self.mapped_types)
@@ -924,7 +956,8 @@ def _map_unmapped_relationships(self) -> None:
                 if type_name not in self.mapped_interfaces:
                     unmapped_interface_models.add(model)
             for model in unmapped_models:
-                self.type(model)(type(self.model_to_type_name(model), (object,), {}))
+                self.type(model)(
+                    type(self.model_to_type_name(model), (object,), {}))
             for model in unmapped_interface_models:
                 self.interface(model)(
                     type(self.model_to_interface_name(model), (object,), {})