Python list to PostgreSQL HSTORE via SQLAlchemy

Question

I'd like to store Python dicts containing lists as HSTORE object in a PostgreSQL database using SQLAlchemy. Following my table class.

from sqlalchemy.dialects.postgresql import HSTORE
from sqlalchemy import Column, String
from sqlalchemy.ext.declarative import declarative_base

Base = declarative_base()

class Data(Base):
    id = Column(String, primary_key=True)
    data = Column(HSTORE)

I insert my items in the following matter.

data = Data(
    id='fancy_id',
    data={
        'foo': ['bar', 'bar']
    },
)

db.Session.add(scan)
db.Session.commit()

This causes a ROLLBACK to happen and the following exception raises.

sqlalchemy.exc.DataError: (psycopg2.errors.ArraySubscriptError) wrong number of array subscripts

[SQL: INSERT INTO data (id, data) VALUES (%(id)s, %(data)s)]
[parameters: {'id': 'fancy_id', 'data': {'foo': ['bar', 'bar']}}]

However, the insertion works without the list.

data = Data(
    id='fancy_id',
    data={
        'foo': 'bar'
    },
)

I followed the PostgreSQL SQLAlchemy 1.4 documentation and can't spot a note indicating this limitation. Am I missing something? How can I store Python lists inside PostgreSQL HSTORE objects via SQLAlchemy?

Thanks in advance.

user7070613 · Accepted Answer · 2021-10-15 14:24:38Z

4

Honestly for this sort of thing json/jsonb would be a better option. Then you would have a direct mapping of Python dict with list to JSON object with array. If you want to use hstore then:

create table hstore_test(id int, hs_fld hstore);
insert into hstore_test values (1, 'a=>1');
insert into hstore_test values (1, 'b=>"[1,2]"'::hstore);
select * from hstore_test ;
 id |    hs_fld    
----+--------------
  1 | "a"=>"1"
  1 | "b"=>"[1,2]"

--So for your example

data={
        'foo': "['bar', 'bar']"
    },

answered Oct 15, 2021 at 14:24

user7070613

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