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/Column.py

@@ -0,0 +1,75 @@
+# -*- coding: utf-8 -*-
+
+from typing import Optional, Any
+
+import abc
+
+from ...log import *
+
+from .DataType import DataType
+
+class Column(abc.ABC): # export
+
+    def __init__(self, table, name, data_type: DataType):
+        self.__name: str = name
+        self.__table: Any = table
+        self.__is_nullable: Optional[bool] = None
+        self.__is_null_insertible: Optional[bool] = None
+        self.__is_primary_key: Optional[bool] = None
+        self.__default_value: Optional[Any] = None
+        self.__default_value_cached: bool = False
+        self.__is_auto_increment: Optional[bool] = None
+        self.__data_type: DataType = data_type
+
+    def __repr__(self):
+        return f'{self.__table.name}.{self.__name}: {self.__data_type}'
+
+    @property
+    def name(self) -> str:
+        return self.__name
+
+    @property
+    def data_type(self):
+        return self.__data_type
+
+    @property
+    def table(self) -> str:
+        return self.__table
+
+    @property
+    def is_nullable(self) -> bool:
+        if self.__is_nullable is None:
+            self.__is_nullable = self.__name in self.__table.nullable_columns
+        return self.__is_nullable
+
+    @property
+    def is_null_insertible(self):
+        if self.__is_null_insertible is None:
+            ret = False
+            if self.is_nullable:
+                ret = True
+            elif self.is_auto_increment:
+                ret = True
+            elif self.default_value is not None:
+                ret = True
+            self.__is_null_insertible = ret
+        return self.__is_null_insertible
+
+    @property
+    def is_primary_key(self) -> bool:
+        if self.__is_primary_key is None:
+            self.__is_primary_key = self.__name in self.__table.primary_keys
+        return self.__is_primary_key
+
+    @property
+    def is_auto_increment(self) -> bool:
+        if self.__is_auto_increment is None:
+            self.__is_auto_increment = self.__name in self.__table.auto_increment_columns
+        return self.__is_auto_increment
+
+    @property
+    def default_value(self) -> Optional[Any]:
+        if self.__default_value_cached is False:
+            self.__default_value = self.__table.column_default(self.name)
+            self.__default_value_cached = True
+        return self.__default_value