SQLAlchemy Columns 结果处理

2022-01-14 00:00:00 python sqlalchemy field db2

问题描述

我正在使用 ibm_db2 驱动程序和 sqlalchemy 处理 IBM DB2 数据库.我的模型是:

I'm working with a IBM DB2 database using ibm_db2 driver and sqlalchemy. My model is:

class User(Model):
    id          = Column('UID', Integer, primary_key=True)
    user        = Column('USER', String(20))
    password    = Column('PASSWORD', String(10))
    name        = Column('NAME', String(30))

数据库中的字符串字段(例如 name)采用以下形式:

String fields from the database (e.g. name) comes in the form of:

>>> "John                                "

，其中值由模式填充到字段的完整长度.

, where the value is filled right with blanks to the full length of the field by schema.

我需要将此行为更改为在 query.all():

I need to change this behavior to the sqlalchemy type String (or a derivative thereof) produced follow (e.g. value.strip()) before output results by query.all():

>>> "John"

我该怎么做?

@property 装饰器不适用.我需要更改标准 sqlalchemy String 类的行为.

@property decorator is not applicable. I need to change the behavior of a standard sqlalchemy String class.

解决方案

我不想改变标准 String 的行为，而是创建一个新类型(然后你可以将它重命名为 String per module based 或其他)但是这样最干净:

I would not want to change the behaviour of the standard String but to make a new type (you can then rename it to String per module basis or whatever) but it is cleanest that way:

from sqlalchemy import types

class StrippedString(types.TypeDecorator):
    """
    Returns CHAR values with spaces stripped
    """

    impl = types.String

    def process_bind_param(self, value, dialect):
        "No-op"
        return value

    def process_result_value(self, value, dialect):
        """
        Strip the trailing spaces on resulting values.
        If value is false, we return it as-is; it might be none
        for nullable columns
        """
        return value.rstrip() if value else value

    def copy(self):
        "Make a copy of this type"
        return StrippedString(self.impl.length)

现在您可以使用 StrippedString 代替 String

Now you can use StrippedString instead of String

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