schema: Continue

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

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

@@ -20,10 +20,27 @@ class Column(abc.ABC): # export
         self.__default_value_cached: bool = False
         self.__is_auto_increment: Optional[bool] = None
         self.__data_type: DataType = data_type
+        self.__foreign_keys: Optional[Any] = None
+        self.__foreign_keys_cached: bool = False
+        self.__foreign_keys_by_table: Optional[dict[str, Any]] = None
 
     def __repr__(self):
         return f'{self.__table.name}.{self.__name}: {self.__data_type}'
 
+    def __eq__(self, rhs) -> bool:
+        if isinstance(rhs, Column):
+            if self.__table != rhs.__table:
+                return False
+            if self.__name != rhs.__name:
+                return False
+            return True
+        elif isinstance(rhs, str):
+            if self.__name != rhs:
+                return False
+            return True
+        throw(ERR, f'Tried to compare column {self} to type {type(rhs)}: {rhs}')
+        return False # Unreachable but requested by mypy
+
     @property
     def name(self) -> str:
         return self.__name
@@ -73,3 +90,25 @@ class Column(abc.ABC): # export
             self.__default_value = self.__table.column_default(self.name)
             self.__default_value_cached = True
         return self.__default_value
+
+    # Returns Column object on parent table
+    @property
+    def foreign_keys(self) -> Optional[Any]:
+        if not self.__foreign_keys_cached:
+            fks: list[Any] = []
+            for cfk in self.__table.foreign_key_constraints:
+                for fk in cfk:
+                    if fk.child_column == self:
+                        fks.append(fk.parent_column)
+            self.__foreign_keys_cached = True
+            self.__foreign_keys = fks if fks else None
+        return self.__foreign_keys
+
+    def foreign_key(self, table) -> Optional[Any]:
+        if self.__foreign_keys_by_table is None:
+            self.__foreign_keys_by_table = dict()
+            for col in self.foreign_keys: # type: ignore # Any not iterable
+                assert(col.table.name not in self.__foreign_keys_by_table)
+                self.__foreign_keys_by_table[col.table.name] = col
+        table_name = table if isinstance(table, str) else table.name
+        return self.__foreign_keys_by_table.get(table_name)