I am trying to write a bulk upsert in python using the SQLAlchemy module (not in SQL!).
I am getting the following error on a SQLAlchemy add:
sqlalchemy.exc.IntegrityError: (IntegrityError) duplicate key value violates unique constraint "posts_pkey"
DETAIL: Key (id)=(TEST1234) already exists.
I have a table called posts
with a primary key on the id
column.
In this example, I already have a row in the db with id=TEST1234
. When I attempt to db.session.add()
a new posts object with the id
set to TEST1234
, I get the error above. I was under the impression that if the primary key already exists, the record would get updated.
How can I upsert with Flask-SQLAlchemy based on primary key alone? Is there a simple solution?
If there is not, I can always check for and delete any record with a matching id, and then insert the new record, but that seems expensive for my situation, where I do not expect many updates.
There is an upsert-esque operation in SQLAlchemy:
db.session.merge()
After I found this command, I was able to perform upserts, but it is worth mentioning that this operation is slow for a bulk "upsert".
The alternative is to get a list of the primary keys you would like to upsert, and query the database for any matching ids:
# Imagine that post1, post5, and post1000 are posts objects with ids 1, 5 and 1000 respectively
# The goal is to "upsert" these posts.
# we initialize a dict which maps id to the post object
my_new_posts = {1: post1, 5: post5, 1000: post1000}
for each in posts.query.filter(posts.id.in_(my_new_posts.keys())).all():
# Only merge those posts which already exist in the database
db.session.merge(my_new_posts.pop(each.id))
# Only add those posts which did not exist in the database
db.session.add_all(my_new_posts.values())
# Now we commit our modifications (merges) and inserts (adds) to the database!
db.session.commit()