Returning Postgres JSON view as JSON string without serialization

[Stephan Hügel]

I’m querying a Postgres view which returns JSON (SELECT json_build_object(…)) which I’ve declared as a view in my db:

allinfra = Table("allinfra", db.metadata, autoload_with=db.engine)

res = db.session.query(allinfra).scalar()

But this gives me a Python dict, when what I want is the JSON string returned by the view - serializing it with json.dumps() on the Python side defeats the point (getting Postgres to do the heavy lifting). Apologies if this question has an obvious answer, but I’ve found it impossible to search for.

[Mike Bayer]

psycopg2 driver (if that's what you're using) jumps in to do the JSON so if you dont want json you need to cast as a string, like cast(table.c.json_col, String).

if you are using a Table with autoload you'd want to override this type using the technique detailed at https://docs.sqlalchemy.org/en/14/core/reflection.html#overriding-reflected-columns .

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[Mike Bayer]

oh also, if this is a view, much easier, just put the CAST to TEXT in your CREATE VIEW statement.  that way you will definitely get strings back and nothing json related will kick in client side.

[Stephan Hügel]

Thanks Mike, wrapping the view declaration with ()::TEXT worked perfectly, but good to know I can do it from SQLA at load time if need be.