schema.Table: Add property relationships

Signed-off-by: Jan Lindemann <jan@janware.com>

tools/python/jwutils/db/schema/Table.py

@@ -1,6 +1,6 @@
 # -*- coding: utf-8 -*-
 
-from typing import Optional, Iterable, Any # TODO: Need any for many things, as I can't figure out how to avoid circular imports from here
+from typing import Optional, Union, Iterable, Self, Any # TODO: Need any for many things, as I can't figure out how to avoid circular imports from here
 
 import abc
 from collections import OrderedDict
@@ -38,7 +38,9 @@ class Table(abc.ABC): # export
         self.__location_rule: Optional[Iterable[str]]  = None
         self.__row_location_rule: Optional[Iterable[str]]  = None
         self.__foreign_keys_to_parent_table: Optional[OrderedDict[str, Any]] = None
+        self.__relationships: Optional[list[tuple[str, Self]]] = None
         self.__model_class: Optional[Any] = None
+        self.__relationship_by_foreign_table: Optional[dict[str, Self]] = None
 
     @property
     def __columns(self) -> OrderedDict[str, Any]:
@@ -134,6 +136,9 @@ class Table(abc.ABC): # export
     def _query_name(self) -> str:
         return 'tbl/' + self.__name
 
+    def _relationships(self) -> list[Self]:
+        return []
+
     @abc.abstractmethod
     def _row_query_name(self) -> str:
         return 'row/' + self.__name
@@ -336,3 +341,22 @@ class Table(abc.ABC): # export
                 self.__foreign_keys_to_parent_table[pt].append(cfk)
         parent_table_name = parent_table if isinstance(parent_table, str) else parent_table.name
         return self.__foreign_keys_to_parent_table[parent_table_name]
+
+    @property
+    def relationships(self) -> list[tuple[str, Self]]:
+        if self.__relationships is None:
+            ret = []
+            for member_name, table_name in self._relationships():
+                ret.append((member_name, self.schema[table_name]))
+            self.__relationships = ret
+        return self.__relationships
+
+    def relationship(self, table: Union[Self, str]) -> bool:
+        if isinstance(table, Table):
+            table = table.name
+        if self.__relationship_by_foreign_table is None:
+            ret: dict[str, Self] = dict()
+            for member_name, table_name in self.relationships:
+                ret[member_name] = self.schema[table_name]
+            self.__relationship_by_foreign_table = ret
+        return self.__relationship_by_foreign_table.get(table)