JSON Schema validation in PostgreSQL?

Question

I can't find any information about JSON schema validation in PostgreSQL, is there any way to implement JSON Schema validation on PostgreSQL JSON data type?

Answer 1

There is a PostgreSQL extension that implements JSON Schema validation in PL/PgSQL.

It is used like this (taken from the project README file):

CREATE TABLE example (id serial PRIMARY KEY, data jsonb);
ALTER TABLE example ADD CONSTRAINT data_is_valid CHECK (validate_json_schema('{"type": "object"}', data));

INSERT INTO example (data) VALUES ('{}');
-- INSERT 0 1

INSERT INTO example (data) VALUES ('1');
-- ERROR:  new row for relation "example" violates check constraint "data_is_valid"
-- DETAIL:  Failing row contains (2, 1).

Answer 2

There is another PostgreSQL extension that implements json validation. The usage is almost the same as "Postgres-JSON-schema"

CREATE TABLE example (id serial PRIMARY KEY, data jsonb);
-- do is_jsonb_valid instead of validate_json_schema
ALTER TABLE example ADD CONSTRAINT data_is_valid CHECK (is_jsonb_valid('{"type": "object"}', data));

INSERT INTO example (data) VALUES ('{}');
-- INSERT 0 1

INSERT INTO example (data) VALUES ('1');
-- ERROR:  new row for relation "example" violates check constraint "data_is_valid"
-- DETAIL:  Failing row contains (2, 1).

I've done some benchmarking validating tweets and it is 20x faster than "Postgres-JSON-schema", mostly because it is written in C instead of SQL.

Disclaimer, I've written this extension.

Answer 3

What you need is something to translate JSON Schema constraints into PostgreSQL ones, e.g.:

{
    "properties": {
        "age": {"minimum": 21}
    },
    "required": ["age"]
}

to:

SELECT FROM ...
WHERE (elem->>'age' >= 21)

I'm not aware of any existing tools. I know of something similar for MySQL which might be useful for writing your own, but nothing for using the JSON type in PostgreSQL.