How to refer to columns whose names begin with a number when autoloading?

[Rob Rosenfeld]

Hi All,

I'm using SQLAlchemy to access a legacy MSSQL database.   I'm using the autoload feature to load the schema from the database.

In this example I'd like to read data out of the column named "1st_period" in the database.   The following query shows the SQL I'd need.  But trying to access a property named "1st_period" yields a SyntaxError

Thanks,

Rob

SELECT TOP 10 [1st_period] FROM Students;

class Student(Model):

__table__ = Table("Students", metadata, autoload=True, autoload_with=engine)

@property

def first_period(self):

return self.1st_period

[Richard Damon]

On 4/12/21 12:29 AM, Rob Rosenfeld wrote:
> Hi All,
>
> I'm using SQLAlchemy to access a legacy MSSQL database.   I'm using
> the autoload feature to load the schema from the database.
>
> In this example I'd like to read data out of the column named
> "1st_period" in the database.   The following query shows the SQL I'd
> need.  But trying to access a property named "1st_period" yields a
> SyntaxError
>
> Thanks,
> Rob
>

> SELECTTOP 10[1st_period] FROM Students;

>
> class Student(Model):
> __table__ = Table("Students", metadata, autoload=True,
> autoload_with=engine)
>
> @property
> def first_period(self):
> return self.1st_period

Have you tried using getattr? That might work (if SQLAlchemy isn't doing
something to quote the name to make a valid version.

getattr(self, '1st_period') would be the equivalent of self.1st_period,
but not have the name parsed by Python.

--
Richard Damon

[r...@rosenfeld.to]

Yep.  That seems fine.  Thanks.  

SQLAlchemy doesn't escape or quote the name.   I checked using

    inspection = inspect(Student)
    return [c_attr.key for c_attr in inspection.mapper.column_attrs]

[Mike Bayer]

besides the idea of using getattr(), as these are object attributes it's probably a good idea to name them differently from those columns.  See the docs at https://docs.sqlalchemy.org/en/14/orm/mapping_columns.html#naming-columns-distinctly-from-attribute-names for strategies on how to achieve this.

--

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http://www.sqlalchemy.org/

 

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[r...@rosenfeld.to]

Thanks for the documentation.  Sorry, but I'm not certain how to apply that in my case.  Since I am mapping to an existing table, how could I reference the object attribute with an illegal name in Python?   Do I combine getattr with the documentation as below?

    class Student(Model):

        __table__ = Table("Students", metadata, autoload=True, autoload_with=engine)

        first_period = getattr(__table__.c, "1st_period")

Thanks,
Rob

[Mike Bayer]

the next section at https://docs.sqlalchemy.org/en/14/orm/mapping_columns.html#automating-column-naming-schemes-from-reflected-tables shows how to automate intercepting of reflected columns, so you could do this:

from sqlalchemy import event

@event.listens_for(metadata, "column_reflect")

def column_reflect(inspector, table, column_info):

    entries = {

        "1st": "first",

        "2nd": "second",

        "3rd": "third",

        "4th": "fourth"

    }

    for prefix in entries:

        if prefix in column["name"]:

            column["key"] = column["name"].replace(prefix, entries[prefix])

            break

class Student(Model):

    __table__ = Table("Students", metadata, autoload=True, autoload_with=engine)

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[r...@rosenfeld.to]

Thanks.   That worked, too.