python - 高效查询多列 SQLAlchemy ORM

Question

我正在尝试使用 SQL Alchemy 进行查询，但我想从包含大约 57 列的表中“选择”20 列，我知道执行此操作的方法是

session.query(Table.col1, Table.col2, Table.col3, Table.col4......).all()

但是效率太低了，而且肯定有更好的方法来做到这一点。

我尝试过但不成功，但已经非常接近的是:

# "columns" is a dictionary that contains all the column names, it looks more or less like this (shorter version

columns = {"Account ID": "AR3",
         "Account Origination Month": "AR55",
         "Origination balance": "AR66",
         "Product": "AR10",
         "Repayment Type": "AR69",
         "Original Loan Term (in months)": "AR61",
         "Initial Product Term (in months)": "AR106",
         "Initial rate/margin": "AR109",
         "Initial Rate Type": "AR107",
         "Reversion margin": "AR119",}



columns_sqla = ", ".join(["Table."+str(value) for key, value in columns.items()])

>>> columns_sqla

'BoE.AR3, BoE.AR55, BoE.AR66, BoE.AR10, BoE.AR69, BoE.AR61, BoE.AR106, BoE.AR109, BoE.AR107, BoE.AR119'

然后我这样做:

session.query(columns_sqla)

但是它会抛出错误，因为它是一个字符串并且它无法识别它。

Answer 1

您可以尝试如下所述的变量解包机制:

session.query(*columns.values()).all()

还可以运行以下代码以进行更简单的说明。

Tuple = lambda *args: args
Dict = lambda **kwargs: kwargs
Print(Tuple(*columns))# PRINT KEYS
Print(columns.Keys())# PRINT KEYS
Print(Dict(**columns))# PRINT DICT ITEMS
Print(columns)# PRINT DICT ITEMS