I looked at lots of alternatives. But I needed something that supported the actual underlying Postgresql json type. Psycopg2 converts those automatically into Python types. So we needed a JSON type that would accept: Python dicts, lists, strings, and JSON encoded objects, lists, and strings. None of them support that because they are all just storing the data as text in the backend.
I haven't looked into the postgres json field in depth yet, but it seems like you may know the answer. Is there any way of ensuring the structure / integrity of the data stored in it? Or is it currently considered to be totally freeform?
Thanks for the info - I'm thinking more along the lines of constraining the data within the valid json.
Just found this post which shows how you can do it.
CREATE TABLE products (
data JSON,
CONSTRAINT validate_id CHECK ((data->>'id')::integer >= 1 AND (data->>'id') IS NOT NULL ),
CONSTRAINT validate_name CHECK (length(data->>'name') > 0 AND (data->>'name') IS NOT NULL ),
CONSTRAINT validate_description CHECK (length(data->>'description') > 0 AND (data->>'description') IS NOT NULL ),
CONSTRAINT validate_price CHECK ((data->>'price')::decimal >= 0.0 AND (data->>'price') IS NOT NULL),
CONSTRAINT validate_currency CHECK (data->>'currency' = 'dollars' AND (data->>'currency') IS NOT NULL),
CONSTRAINT validate_in_stock CHECK ((data->>'in_stock')::integer >= 0 AND (data->>'in_stock') IS NOT NULL )
}
Why would you ever want to do this? Surely at this point you are better with a table with id, name, description, price, currency, in_stock and an extra data field for anything else - given you require the other fields.
Maybe - I need to test the performance, but for my application breaking things out into a table is a little slow. In all probability the constraints will be slower, but it's something to try.
At the moment I have all my data in mongo but over time it's fallen out of shape. There's a large chunk of it that just needs to be stores (json field) but it would be nice to constrain some of it.
Depends on how much the data is going to be altered. Changing columns is not a free operation in data stores. They require you to rewrite all the rows in many cases.
Not properly using Django's ORM. That's something I'll write when we actually start to need it. At the moment. It's more of a wholesale document store. Right now you would have to write a custom SQL query, using the Postgresql JSON functions, and the Model.objects.raw(...) interface of provided by Django.
