The json component

For advanced users, allows you to easily build an API over your database. The json component responds to the current HTTP request with a JSON object. This component must appear at the top of your SQL file, before any other data has been sent to the browser.

Send query results as a JSON array

SQL

select 'json' AS component;
select * from users;

Result

[
    {"username":"James","userid":1},
    {"username":"John","userid":2}
]

Send a single JSON object

SQL

select 'json' AS component, 'jsonlines' AS type;
select * from users where id = $user_id LIMIT 1;

Note the LIMIT 1 clause. The jsonlines type will send one JSON object per result row, separated only by a single newline character (\n). So if your query returns multiple rows, the result will not be a single valid JSON object, like most JSON parsers expect.

Result

{ "username":"James", "userid":1 }

Create a complex API endpoint

You can create an API endpoint that will return a JSON value in any format you want, to implement a complex API.

You should use the json functions provided by your database to form the value you pass to the contents property. To build a json array out of rows from the database, you can use:

• json_group_array() in SQLite,

• json_agg() in Postgres, or

• JSON_ARRAYAGG() in MySQL.

• FOR JSON PATH in SQL Server.

SELECT 'json' AS component, 
        JSON_OBJECT(
            'users', (
                SELECT JSON_GROUP_ARRAY(
                    JSON_OBJECT(
                        'username', username,
                        'userid', id
                    )
                ) FROM users
            )
        ) AS contents;

This will return a JSON response that looks like this:

{ 
    "users" : [
        { "username":"James", "userid":1 }
    ]
}

If you want to handle custom API routes, like POST /api/users/:id, you can use

• the 404.sql file to handle the request despite the URL not matching any file,
• the request_method function to differentiate between GET and POST requests,
• and the path function to extract the :id parameter from the URL.

Access query results in real-time with server-sent events

Using server-sent events, you can stream large query results to the client in real-time, row by row.

This allows building sophisticated dynamic applications that will start processing and displaying the first rows of data in the browser while the database server is still processing the end of the query.

SQL

select 'json' AS component, 'sse' AS type;
select * from users;

JavaScript

const eventSource = new EventSource("users.sql");
eventSource.onmessage = function (event) {
    const user = JSON.parse(event.data);
    console.log(user.username);
}
eventSource.onerror = function () {
    eventSource.close(); // do not reconnect after reading all the data
}