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/Schema.py

@@ -0,0 +1,78 @@
+# -*- coding: utf-8 -*-
+
+from typing import Optional, List, Iterable
+
+import abc
+
+from ...log import *
+
+from .Table import Table
+from .Column import Column
+from .DataType import DataType
+from .CompositeForeignKey import CompositeForeignKey
+
+class Schema(abc.ABC): # export
+
+    def __init__(self) -> None:
+        self.___tables: Optional[List[Table]] = None
+        self.__foreign_keys: Optional[List[CompositeForeignKey]] = None
+
+    @property
+    def __tables(self):
+        if self.___tables is None:
+            ret = dict()
+            for name in self._table_names():
+                slog(WARNING, f'Caching metadata for table "{name}"')
+                assert(isinstance(name, str))
+                ret[name] = self._table(name)
+            self.___tables = ret
+        return self.___tables
+
+    # ------ API to be implemented
+
+    @abc.abstractmethod
+    def _table_names(self) -> Iterable[str]:
+        throw(ERR, "Called pure virtual base class method")
+        return []
+
+    @abc.abstractmethod
+    def _table(self, name: str) -> Table:
+        throw(ERR, "Called pure virtual base class method")
+        return None # type: ignore
+
+    @abc.abstractmethod
+    def _foreign_keys(self) -> List[CompositeForeignKey]:
+        pass
+
+    # ------ API to be called
+
+    @property
+    def table_names(self) -> Iterable[str]:
+        return self.__tables.keys()
+
+    @property
+    def tables(self) -> Iterable[Table]:
+        return self.__tables.values()
+
+    @property
+    def foreign_key_constraints(self) -> List[CompositeForeignKey]:
+        if self.__foreign_keys is None:
+            self.__foreign_keys = self._foreign_keys()
+        return self.__foreign_keys
+
+    def table(self, name: str) -> Table:
+        return self.__tables[name]
+
+    def table_by_model_name(self, name: str, throw=False) -> Table:
+        for table in self.__tables.values():
+            if table.model_name == name:
+                return table
+        if throw:
+            raise Exception(f'Table "{name}" not found in database metadata')
+        return None # type: ignore
+
+    def primary_keys(self, table_name: str) -> Iterable[str]:
+        return self.__tables[table_name].primary_keys
+
+    def columns(self, table_name: str) -> Iterable[Column]:
+        return self.__tables[table_name].columns