Add db.schema framework

jw.db.schema is a set of classes meant as an interface to describe a database schema.

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

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

@@ -0,0 +1,78 @@
+# -*- coding: utf-8 -*-
+
+from typing import Optional, List, Any
+
+from .ColumnSet import ColumnSet
+from .SingleForeignKey import SingleForeignKey
+
+class CompositeForeignKey: # export
+
+    def __init__(self, child_col_set: ColumnSet, parent_col_set: ColumnSet): # TODO: Implement alternative ways to construct
+
+        def __table(s):
+            ret = None
+            for c in s:
+                if ret is None:
+                    ret = c.table
+                else:
+                    assert(ret == c.table)
+            assert(ret is not None)
+            return ret
+
+        self.__child_col_set = child_col_set
+        self.__parent_col_set = parent_col_set
+        self.__child_table = __table(child_col_set)
+        self.__parent_table = __table(parent_col_set)
+
+        assert(len(self.__child_col_set) == len(self.__parent_col_set))
+        self.__len = len(self.__child_col_set)
+        self.__column_relations: Optional[List[SingleForeignKey]] = None
+
+    def __table_rel_str(self):
+        return f'{self.__child_table.name} => {self.__parent_table.name}'
+
+    def __cols_rel_str(self, child, parent):
+        return f'{child.name} -> {parent.name}'
+
+    def __len__(self):
+        return self.__len
+
+    def __iter__(self):
+        yield from self.column_relations
+
+    def __repr__(self):
+        ret = self.__table_rel_str()
+        ret += '|| ' + ' | '.join([self.__cols_rel_str(rel.child_col, rel.parent_col) for rel in self.column_relations])
+        return ret
+
+    def __eq__(self, rhs):
+        if rhs.__child_col_set != self.__child_col_set:
+            return False
+        if rhs.__parent_col_set != self.__parent_col_set:
+            return False
+        return True
+
+    @property
+    def child_table(self) -> Any:
+        return self.__child_table
+
+    @property
+    def parent_table(self) -> Any:
+        return self.__parent_table
+
+    @property
+    def child_columns(self) -> ColumnSet:
+        return self.__child_col_set
+
+    @property
+    def parent_columns(self) -> ColumnSet:
+        return self.__parent_col_set
+
+    @property
+    def column_relations(self) -> List[Any]:
+        ret = []
+        if self.__column_relations is None:
+            for i in range(0, self.__len):
+                ret.append(SingleForeignKey(self.__child_col_set[i], self.__parent_col_set[i]))
+            self.__column_relations = ret
+        return self.__column_relations