pg_jsonschema: JSON Schema Validation - Supabase

JSON Schema is a language for annotating and validating JSON documents. pg_jsonschema is a Postgres extension that adds the ability to validate PostgreSQL's built-in json and jsonb data types against JSON Schema documents.

Enable the extension

<Tabs scrollable size="small" type="underlined" defaultActiveId="dashboard" queryGroup="database-method"

Go to the Database page in the Dashboard.
Click on Extensions in the sidebar.
Search for pg_jsonschema and enable the extension.

</TabPanel> <TabPanel id="sql" label="SQL"> ```sql -- Enable the "pg_jsonschema" extension create extension pg_jsonschema with schema extensions;

-- Disable the "pg_jsonschema" extension drop extension if exists pg_jsonschema;


Even though the SQL code is `create extension`, this is the equivalent of enabling the extension.
To disable an extension you can call `drop extension`.

It's good practice to create the extension within a separate schema (like `extensions`) to keep the `public` schema clean.

</TabPanel>
</Tabs>

## Functions

- [`json_matches_schema(schema json, instance json)`](https://github.com/supabase/pg_jsonschema#api): Checks if a `json` _instance_ conforms to a JSON Schema _schema_.
- [`jsonb_matches_schema(schema json, instance jsonb)`](https://github.com/supabase/pg_jsonschema#api): Checks if a `jsonb` _instance_ conforms to a JSON Schema _schema_.

## Usage

Since `pg_jsonschema` exposes its utilities as functions, we can execute them with a select statement:
```sql
select
  extensions.json_matches_schema(
    schema := '{"type": "object"}',
    instance := '{}'
  );

pg_jsonschema is generally used in tandem with a check constraint as a way to constrain the contents of a json/b column to match a JSON Schema.

sql

create table customer(
    id serial primary key,
    ...
    metadata json,

    check (
        json_matches_schema(
            '{
                "type": "object",
                "properties": {
                    "tags": {
                        "type": "array",
                        "items": {
                            "type": "string",
                            "maxLength": 16
                        }
                    }
                }
            }',
            metadata
        )
    )
);

-- Example: Valid Payload
insert into customer(metadata)
values ('{"tags": ["vip", "darkmode-ui"]}');
-- Result:
--   INSERT 0 1

-- Example: Invalid Payload
insert into customer(metadata)
values ('{"tags": [1, 3]}');
-- Result:
--   ERROR:  new row for relation "customer" violates check constraint "customer_metadata_check"
--   DETAIL:  Failing row contains (2, {"tags": [1, 3]}).

Resources

Official pg_jsonschema documentation