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我正在开发一个小工具，它能够读取文件的低级数据，即映射等，并将结果存储到 sqlite DB，使用 python 的内置 sqlite API。

对于解析的文件数据，我有 3 个类：

class GenericFile: # general file class 
    # bunch of methods here
    ...
class SomeFileObject_A: # low level class for storing objects of kind SomeFileObject_A
    # bunch of methods here
    ...
class SomeFileObject_B: # low level cass for storing objects of kind SomeFileObject_A
    # bunch of methods here
    ...

sqlite 接口被实现为一个单独的类：

class Database:
    def insert(self, object_to_insert):
    ...
    def _insert_generic_file_object(self, object_to_insert):
    ...
    def _insert_file_object_a(self, object_to_insert):
    ...
    def _insert_file_object_b(self, object_to_insert):
    ...
    # bunch of sqlite related methods

当我需要向 DB 插入一些对象时，我正在使用db.insert(object).

现在我认为isinstance在我的insert方法中使用它可能是个好主意，因为它可以处理任何插入的对象，而无需为每个对象显式调用合适的方法，这看起来更优雅。但是在阅读更多内容后isinstance，我开始怀疑我的设计不是那么好。

这是通用insert方法的实现：

class Database:
    def insert(self, object_to_insert):
        self._logger.info("inserting %s object", object_to_insert.__class__.__name__)
        if isinstance(object_to_insert, GenericFile):
            self._insert_generic_file_object(object_to_insert)
        elif isinstance(object_to_insert, SomeFileObject_A):
            self._insert_file_object_a(object_to_insert)
        elif isinstance(object_to_insert, SomeFileObject_B):
            self._insert_file_object_b(object_to_insert)
        else:
            self._logger.error("Insert Failed. Bad object type %s" % type(object_to_insert))
            raise Exception
        self._db_connection.commit()

所以，isinstace在我的情况下应该避免，如果应该，这里有什么更好的解决方案？

谢谢

4

1 回答 1

1

OO 中的基本原则之一是用多态调度替换显式开关。在您的情况下，解决方案是使用双重调度，因此FileObect知道要调用哪个Database方法是 ' 的责任，即：

class GenericFile: # general file class 
    # bunch of methods here
    ...
    def insert(self, db):
        return db.insert_generic_file_object(self)


class SomeFileObject_A: # low level class for storing objects of kind SomeFileObject_A
    # bunch of methods here
    ...
    def insert(self, db):
        return db.insert_file_object_a(self)


class SomeFileObject_B: # low level cass for storing objects of kind SomeFileObject_A
    # bunch of methods here
    ...
    def insert(self, db):
        return db.insert_file_object_b(self)


class Database:
    def insert(self, obj):
        return obj.insert(self)
于 2015-12-29T08:57:51.553 回答