Problem
I want to add a comment to a number of columns from Python in a PostgreSQL database.
If I run the statement that my Python script produces in a database client manually everything works as it should.
If I let Python run the statement via an sqlalchemy engine, nothing is updated.
Details
I have a dictionary in Python of the form { 'column name': 'column comment with some text'}.
I want to add this comments to an existing table in a Postgres database.
Manually I would run the following command in Postgres:
comment on column schema.table."column name" is 'column comment with some text'
Now in Python I want to run the same, but then looping over the dictionary. This is the code I use:
from sqlalchemy import create_engine, text
db = create_engine(f"postgresql://PGUSER:PGPASSWORD@PGHOST/PGDATABASE")
coldict = {'col1': 'col1 contains this data, etc... some more comments', 'col2': 'col2 shows something.'}
with db.connect() as con:
for key in coldict:
colname = key
# Convert a single quote to two single quotes as that is what SQL likes.
colcomm = coldict[key].translate(str.maketrans({"'": "''"}))
stmt = f"comment on column schema.table.\"{colname}\" is '{colcomm}';"
# print the statement that will be run for debugging
print(stmt)
# execute statement in database
con.execute(text(stmt))
This prints out:
comment on column schema.table."col1" is 'col1 contains this data, etc... some more comments';
comment on column schema.table."col2" is 'col2 shows something.';
When I check the column comments with the query from this answer no comments are actually set.
If I copy-paste what is printed out into a database client and run it there, the column comment is updated as it should.
How can I update the column comment via a loop in Python?