Cannot Query Array of Integers in Postgres - arrays

Question

Migrated column type from HSTORE to JSONB and am using this snippet of code...
from sqlalchemy.dialects.postgresql import ARRAY, JSONB
if employment_type:
base = base.filter(Candidate.bio["employment_type"].cast(ARRAY).contains(employment_type))
and am getting this error...
127.0.0.1 - - [28/Mar/2016 12:25:13] "GET /candidate_filter/?employment_type_3=true HTTP/1.1" 500 -
Traceback (most recent call last):
File "/Library/Python/2.7/site-packages/flask/app.py", line 1836, in __call__
return self.wsgi_app(environ, start_response)
File "/Library/Python/2.7/site-packages/flask/app.py", line 1820, in wsgi_app
response = self.make_response(self.handle_exception(e))
File "/Library/Python/2.7/site-packages/flask/app.py", line 1403, in handle_exception
reraise(exc_type, exc_value, tb)
File "/Library/Python/2.7/site-packages/flask/app.py", line 1817, in wsgi_app
response = self.full_dispatch_request()
File "/Library/Python/2.7/site-packages/flask/app.py", line 1477, in full_dispatch_request
rv = self.handle_user_exception(e)
File "/Library/Python/2.7/site-packages/flask/app.py", line 1381, in handle_user_exception
reraise(exc_type, exc_value, tb)
File "/Library/Python/2.7/site-packages/flask/app.py", line 1475, in full_dispatch_request
rv = self.dispatch_request()
File "/Library/Python/2.7/site-packages/flask/app.py", line 1461, in dispatch_request
return self.view_functions[rule.endpoint](**req.view_args)
File "/Users/surajkapoor/Desktop/lhv-talenttracker/app/views.py", line 660, in investor_filter
base = base.filter(Candidate.bio["employment_type"].cast(ARRAY).contains(employment_type))
File "/Library/Python/2.7/site-packages/sqlalchemy/dialects/postgresql/json.py", line 93, in cast
return self.astext.cast(type_)
File "/Library/Python/2.7/site-packages/sqlalchemy/dialects/postgresql/json.py", line 95, in cast
return sql.cast(self, type_)
File "<string>", line 2, in cast
File "/Library/Python/2.7/site-packages/sqlalchemy/sql/elements.py", line 2314, in __init__
self.type = type_api.to_instance(type_)
File "/Library/Python/2.7/site-packages/sqlalchemy/sql/type_api.py", line 1142, in to_instance
return typeobj(*arg, **kw)
TypeError: __init__() takes at least 2 arguments (1 given)
Candidate.bio["employment_type"] is an array of integers and I'm simply trying to query all the rows that contain a specific integer in them.
Also, .cast() works perfectly on the same column when calling Integer...
if internship:
base = base.filter(Candidate.bio["internship"].cast(Integer) == 1)

Answer 1

SqlAlchemy is probably having difficulty constructing the where clause because it can't figure out what type bio->'employment_type' is.
If the contains method is called from a String object, it would generate a LIKE clause, but for JSONB or ARRAY it would need to generate the #> operator.
To give SqlAlchemy the necessary hints, use explicit casting everywhere, i.e. write your query like
from sqlalchemy import cast
if employment_type:
casted_field = Candidate.bio['employment_type'].cast(JSONB)
casted_values = cast(employment_type, JSONB)
stmt = base.filter(casted_field.contains(casted_values))

Answer 2

In my example, I have a JSONB column named bio with the following data:
{"employment_type": [1, 2, 3]}
Edit: Casting to JSONB works:
>>> from sqlalchemy.dialects.postgresql import JSONB
>>> employment_type = 2
>>> query = (
... session.query(Candidate)
... .filter(Candidate.bio['employment_type'].cast(JSONB).contains(employment_type)))
>>> query.one().bio
{"employment_type": [1, 2, 3]}
Original answer:
I couldn't get .contains to work on Candidate.bio['employment_type'], but we can do the equivalent of the following SQL:
SELECT * FROM candidate WHERE candidate.bio #> '{"employment_type": [2]}';
like this:
>>> employment_type = 2
>>> test = {'employment_type': [employment_type]}
>>> query = (
... session.query(Candidate)
... .filter(Candidate.bio.contains(test)))
>>> query.one().bio
{"employment_type": [1, 2, 3]}