https://github.com/piccolo-orm/piccolo_api/discussions/265#discussion…

piccolo/__init__.py

@@ -1 +1 @@
-__VERSION__ = "1.16.0"
+__VERSION__ = "1.16.1.dev2"

piccolo/columns/column_types.py

@@ -2052,7 +2052,8 @@ class Treasurer(Table):
         if not self._meta.unique or any(
             not i._meta.unique for i in self._meta.call_chain
         ):
-            raise ValueError("Only reverse unique foreign keys.")
+            pass
+            # raise ValueError("Only reverse unique foreign keys.")
 
         foreign_keys = [*self._meta.call_chain, self]
 

piccolo/columns/m2m.py

@@ -30,6 +30,7 @@ def __init__(
         m2m: M2M,
         as_list: bool = False,
         load_json: bool = False,
+        reverse: t.Optional[bool] = None,
     ):
         """
         :param columns:
@@ -39,12 +40,15 @@ def __init__(
             flattened list will be returned, rather than a list of objects.
         :param load_json:
             If ``True``, any JSON strings are loaded as Python objects.
+        :param reverse:
+          If ``True``, make reverse query to self reference tables.
 
         """
         self.as_list = as_list
         self.columns = columns
         self.m2m = m2m
         self.load_json = load_json
+        self.reverse = reverse
 
         safe_types = (int, str)
 
@@ -74,20 +78,43 @@ def get_select_string(
         fk_2 = self.m2m._meta.secondary_foreign_key
         fk_2_name = fk_2._meta.db_column_name
         table_2 = fk_2._foreign_key_meta.resolved_references
-        table_2_name = table_2._meta.tablename
-        table_2_name_with_schema = table_2._meta.get_formatted_tablename()
-        table_2_pk_name = table_2._meta.primary_key._meta.db_column_name
-
-        inner_select = f"""
-            {m2m_table_name_with_schema}
-            JOIN {table_1_name_with_schema} "inner_{table_1_name}" ON (
-                {m2m_table_name_with_schema}."{fk_1_name}" = "inner_{table_1_name}"."{table_1_pk_name}"
-            )
-            JOIN {table_2_name_with_schema} "inner_{table_2_name}" ON (
-                {m2m_table_name_with_schema}."{fk_2_name}" = "inner_{table_2_name}"."{table_2_pk_name}"
-            )
-            WHERE {m2m_table_name_with_schema}."{fk_1_name}" = "{table_1_name}"."{table_1_pk_name}"
-        """  # noqa: E501
+        # if primary and secondary table are the same
+        if table_1 == table_2:
+            table_2_name = table_1._meta.tablename
+            table_2_name_with_schema = table_1._meta.get_formatted_tablename()
+            table_2_pk_name = table_1._meta.primary_key._meta.db_column_name
+            # check reverse argument. If True change direction in query
+            if self.reverse: 
+                inner_select = f"""
+                    {m2m_table_name_with_schema}
+                    JOIN {table_1_name_with_schema} "inner_{table_1_name}" ON (
+                        {m2m_table_name_with_schema}."{fk_1_name}" = "inner_{table_1_name}"."{table_1_pk_name}"
+                    )
+                    WHERE {m2m_table_name_with_schema}."{fk_2_name}" = "{table_2_name}"."{table_2_pk_name}"
+                """  # noqa: E501
+            else:
+                inner_select = f"""
+                    {m2m_table_name_with_schema}
+                    JOIN {table_2_name_with_schema} "inner_{table_2_name}" ON (
+                        {m2m_table_name_with_schema}."{fk_2_name}" = "inner_{table_2_name}"."{table_2_pk_name}"
+                    )
+                    WHERE {m2m_table_name_with_schema}."{fk_1_name}" = "{table_1_name}"."{table_1_pk_name}"
+                """  # noqa: E501
+        else:
+            table_2_name = table_2._meta.tablename
+            table_2_name_with_schema = table_2._meta.get_formatted_tablename()
+            table_2_pk_name = table_2._meta.primary_key._meta.db_column_name
+
+            inner_select = f"""
+                {m2m_table_name_with_schema}
+                JOIN {table_1_name_with_schema} "inner_{table_1_name}" ON (
+                    {m2m_table_name_with_schema}."{fk_1_name}" = "inner_{table_1_name}"."{table_1_pk_name}"
+                )
+                JOIN {table_2_name_with_schema} "inner_{table_2_name}" ON (
+                    {m2m_table_name_with_schema}."{fk_2_name}" = "inner_{table_2_name}"."{table_2_pk_name}"
+                )
+                WHERE {m2m_table_name_with_schema}."{fk_1_name}" = "{table_1_name}"."{table_1_pk_name}"
+            """  # noqa: E501
 
         if engine_type in ("postgres", "cockroach"):
             if self.as_list:
@@ -244,9 +271,17 @@ def secondary_foreign_key(self) -> ForeignKey:
         """
         See ``primary_foreign_key``.
         """
+        # if primary and secondary table are the same
         for fk_column in self.foreign_key_columns:
             if fk_column._foreign_key_meta.resolved_references != self.table:
                 return fk_column
+            if (
+                fk_column._foreign_key_meta.resolved_references
+                == self.primary_table
+            ):
+                return self.foreign_key_columns[-1]
+        if self.table == self.primary_table:
+            return self.foreign_key_columns[-1]
 
         raise ValueError("No matching foreign key column found!")
 
@@ -366,29 +401,54 @@ def __await__(self):
 class M2MGetRelated:
     row: Table
     m2m: M2M
+    reverse: t.Optional[bool] = False
 
     async def run(self):
+
         joining_table = self.m2m._meta.resolved_joining_table
 
         secondary_table = self.m2m._meta.secondary_table
+        if self.reverse: 
+            try:
+                ids = (
+                    await joining_table.select(
+                                                getattr(
+                                                    self.m2m._meta.primary_foreign_key,
+                                                    secondary_table._meta.primary_key._meta.name,
+                                                )
+                    )
+                    .where(self.m2m._meta.secondary_foreign_key == self.row)
+                    .output(as_list=True)
+                )
 
-        # TODO - replace this with a subquery in the future.
-        ids = (
-            await joining_table.select(
-                getattr(
-                    self.m2m._meta.secondary_foreign_key,
-                    secondary_table._meta.primary_key._meta.name,
+                results = await secondary_table.objects().where(
+                    secondary_table._meta.primary_key.is_in(ids)
                 )
-            )
-            .where(self.m2m._meta.primary_foreign_key == self.row)
-            .output(as_list=True)
-        )
+            except ValueError:
+                results = []
 
-        results = await secondary_table.objects().where(
-            secondary_table._meta.primary_key.is_in(ids)
-        )
+            return results
+        else:
+            try:
+                # TODO - replace this with a subquery in the future.
+                ids = (
+                    await joining_table.select(
+                                                getattr(
+                                                    self.m2m._meta.secondary_foreign_key,
+                                                    secondary_table._meta.primary_key._meta.name,
+                                                )
+                    )
+                    .where(self.m2m._meta.primary_foreign_key == self.row)
+                    .output(as_list=True)
+                )
+
+                results = await secondary_table.objects().where(
+                    secondary_table._meta.primary_key.is_in(ids)
+                )
+            except ValueError:
+                results = []
 
-        return results
+            return results
 
     def run_sync(self):
         return run_sync(self.run())
@@ -427,6 +487,7 @@ def __call__(
         *columns: t.Union[Column, t.List[Column]],
         as_list: bool = False,
         load_json: bool = False,
+        reverse: t.Optional[bool] = None,
     ) -> M2MSelect:
         """
         :param columns:
@@ -437,6 +498,7 @@ def __call__(
             flattened list will be returned, rather than a list of objects.
         :param load_json:
             If ``True``, any JSON strings are loaded as Python objects.
+
         """
         columns_ = flatten(columns)
 
@@ -449,5 +511,5 @@ def __call__(
             )
 
         return M2MSelect(
-            *columns_, m2m=self, as_list=as_list, load_json=load_json
+            *columns_, m2m=self, as_list=as_list, load_json=load_json, reverse=reverse
         )

piccolo/table.py

@@ -574,14 +574,14 @@ def refresh(
 
     @t.overload
     def get_related(
-        self, foreign_key: ForeignKey[ReferencedTable]
+        self, foreign_key: ForeignKey[ReferencedTable], many: bool = False
     ) -> First[ReferencedTable]: ...
 
     @t.overload
-    def get_related(self, foreign_key: str) -> First[Table]: ...
+    def get_related(self, foreign_key: str, many: bool = False) -> First[Table]: ...
 
     def get_related(
-        self, foreign_key: t.Union[str, ForeignKey[ReferencedTable]]
+        self, foreign_key: t.Union[str, ForeignKey[ReferencedTable]], many: bool = False
     ) -> t.Union[First[Table], First[ReferencedTable]]:
         """
         Used to fetch a ``Table`` instance, for the target of a foreign key.
@@ -612,16 +612,16 @@ def get_related(
 
         references = foreign_key._foreign_key_meta.resolved_references
 
-        return (
-            references.objects()
-            .where(
+        insts = references.objects().where(
                 foreign_key._foreign_key_meta.resolved_target_column
                 == getattr(self, column_name)
             )
-            .first()
-        )
+        if many:
+            return insts
+        return insts.first()
+
 
-    def get_m2m(self, m2m: M2M) -> M2MGetRelated:
+    def get_m2m(self, m2m: M2M, reverse: t.Optional[bool] = None) -> M2MGetRelated:
         """
         Get all matching rows via the join table.
 
@@ -632,7 +632,7 @@ def get_m2m(self, m2m: M2M) -> M2MGetRelated:
             [<Genre: 1>, <Genre: 2>]
 
         """
-        return M2MGetRelated(row=self, m2m=m2m)
+        return M2MGetRelated(row=self, m2m=m2m, reverse=reverse)
 
     def add_m2m(
         self,