如何在SQLAlchemy（PostgreSQL / Python）中的右外部联接样式查询中更新一列？

Question

I have two tables, Table A and Table B . I have added one column to Table A , record_id . Table B has record_id and the primary ID for Table A , table_a_id . I am looking to deprecate Table B .

Relationships exist between Table B 's table_a_id and Table A 's id , if that helps.

Currently, my solution is:

db.execute("UPDATE table_a t 
   SET record_id = b.record_id 
   FROM table_b b 
   WHERE t.id = b.table_a_id")

This is my first time using this ORM -- I'd like to see if there is a way I can use my Python models and the actual functions SQLAlchemy gives me to be more 'Pythonic' rather than just dumping a Postgres statement that I know works in an execute call.

Answer 1

My solution ended up being as follows:

(db.query(TableA)
        .filter(TableA.id == TableB.table_a_id,
        TableA.record_id.is_(None))
        .update({TableA.record_id: TableB.record_id}, synchronize_session=False))

This leverages the ability of PostgreSQL to do updates based on implicit references of other tables, which I did in my .filter() call (this is analogous to a WHERE in a JOIN query). The solution was deceivingly simple.