SQLAlchemy Postgres 查询是 JSON 中存在的关键

Question

I have a model Definition :

class Definition:
    meta = Column(MutableDict.as_mutable(JSON))

It stores any JSON so I want to query if a given key exists in this field.

I need something like:

defs = db.query(Definition).filter(
    Definition.meta.has_key('translation')).all()

MySQL for example has a function named json_contains and I could use it:

defs = db.query(Definition).filter(
    func.json_contains(
        Definition.meta, 'translation') == 1).all()

How can I achieve this in PostgreSQL

Answer 1

Whenever I am unsure of how to use the sqlalchemy bits, I hack a version together, and go from there:

json_select = '''SELECT jdoc->'key_name1', jdoc->'translation'
FROM Definition 
WHERE jdoc @> '{"translation": 1, "key_name1": "hello there"}'
;
'''

print([x for x in db.engine.execute(json_select)])

note:

psycopg2 changed in version 2.5.4: added jsonb support.

Referenced:

• http://initd.org/psycopg/docs/extras.html#json-adaptation
• https://www.postgresql.org/docs/9.4/static/datatype-json.html