当sqlalchemy ORM class 属性与数据库列不同时，如何获取ORM class 属性列表？

Question

假设您想在 sqlalchemy 中迭代 ORM class 的 ORM 属性。因此，您需要一个 ORM 属性列表。您如何获得该列表？

如果 ORM class 没有重命名属性，因此 ORM 属性与数据库列匹配，那么您可以使用以下解决方案：（顺便说一下，源代码文件 /lib/sqlalchemy/orm/base.py 中还有一个内置（私有）函数 _orm_columns() 似乎提供了此功能）

但是如果 python ORM class 与数据库列的名称不同（例如在这 3 个 ORM 属性中）：

>>> class User(Base):
...     __tablename__ = 'users'
...
...     id = Column('pkey', Integer, primary_key=True)
...     name = Column('user_name', String)
...     fullname = Column('human_name', String)

那这个方法就不行了。那么，如何获得 ORM 属性的 python 版本呢？

Answer 1

我定义了一个 mixin class 来扩充

Base = declarative_base()

使用 mixin class 定义为：

import inspect
import sqlalchemy as sqla 

class orm_mixin_class(object):
    """Additional functionality wanted in orm classes (that inherit from Base)."""

    @classmethod
    def orm_class_info(cls):
        """
        Get info about the orm class (as opposed to the database table it is mapped to).

        Returns:
            list of dict where each dict describes a orm class attribute.  
            Keys: s_class_attribute_name
        """
        o_leaf_level_class = cls   # this turns out the be the leaf class instead of this mixin class
        l_orm_attribute_pairs = inspect.getmembers(o_leaf_level_class)

        l_orm_class_info_dicts = []
        for (s_class_attribute_name, o_attr_type) in l_orm_attribute_pairs:
            d_attr_info = {}
            b_orm_attribute = False
            try:
                o_inspect = sqla.inspection.inspect(o_attr_type) 

                if isinstance(o_inspect, sqla.orm.attributes.QueryableAttribute):
                    b_orm_attribute = True
                    d_attr_info['s_class_attribute_name'] = s_class_attribute_name
            except:
                pass            

            if b_orm_attribute:
                # only orm attributes have an entry in the output list
                l_orm_class_info_dicts.append(d_attr_info)

        return(l_orm_class_info_dicts)

因此可以从方法调用中轻松获取 ORM 属性列表。

ORM class 声明现在是：

class User(Base, orm_mixin_class):

Answer 2

这已经使用 inspection system:

实现

from sqlalchemy import *
from sqlalchemy.orm import *
from sqlalchemy.ext.declarative import declarative_base
from sqlalchemy import inspect

Base = declarative_base()

class A(Base):
    __tablename__ = 'a'
    id = Column(Integer, primary_key=True)
    x = Column(Integer)
    y = Column(Integer)

print inspect(A).c
print inspect(A).c.x
print inspect(A).column_attrs
print inspect(A).column_attrs.x
print inspect(A).column_attrs.x.expression

http://docs.sqlalchemy.org/en/latest/core/inspection.html

http://docs.sqlalchemy.org/en/latest/orm/mapping_api.html#sqlalchemy.orm.mapper.Mapper.all_orm_descriptors

http://docs.sqlalchemy.org/en/latest/orm/mapping_api.html#sqlalchemy.orm.mapper.Mapper.columns

http://docs.sqlalchemy.org/en/latest/orm/mapping_api.html#sqlalchemy.orm.mapper.Mapper.column_attrs

http://docs.sqlalchemy.org/en/latest/orm/mapping_api.html#sqlalchemy.orm.mapper.Mapper.c

当sqlalchemy ORM class 属性与数据库列不同时，如何获取ORM class 属性列表？

When the sqlalchemy ORM class attributes are different from database columns, how to get a list of the ORM class attributes?

python

sqlalchemy