How do I get the name of an SQLAlchemy object's primary key?

Question

I just want to programatically determine the name of an SQLalchemy model\'s primary key.

Answer 1

Assuming the declarative model class is User,

>>> list(User.__table__.primary_key)[0].name
'id'

Or for Membership which has a composite primary key

>>> [pk.name for pk in Membership.__table__.primary_key]
['user_id', 'group_id']

Answer 2

If using SQLAlchemy version 0.8 or later, you should use the runtime inspection API.

If the model class is User and the sole primary key is id,

>>> from sqlalchemy.inspection import inspect
>>> inspect(User).primary_key[0].name
'id'

If the model class is User and there are many primary keys,

>>> from sqlalchemy.inspection import inspect
>>> [key.name for key in inspect(User).primary_key]
['id', 'name']

If using SQLAlchemy version less than 0.8, you should use the class_mapper() function instead.

>>> from sqlalchemy.orm import class_mapper
>>> class_mapper(User).primary_key[0].name
'id'

In this case, the inspect() function and the class_mapper() function return the same object, but using inspect() is more future-proof.

Answer 3

If class is "User", and there is just 1 primary key, do this*:

User.__mapper__.primary_key._list[0].name

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^*_{Moved from the question.}