Table Extensions

An extension is a named JSON descriptor on a registered table. It switches optional behaviour on. It changes neither the data nor the schema of the table. Beacon stores an extension with the table. It survives a restart.

Beacon has one extension today:

• preset: define named filter sets. Other features use them by name.

Manage extensions

Set, inspect and remove an extension with SQL DDL. The admin REST API gives the same functions. The value is a JSON object. Each extension has its own shape.

-- Attach or replace an extension
SET EXTENSION '<name>' FOR <table> TO '<json>';

-- List the extensions on a table
SHOW EXTENSIONS FOR <table>;

-- Remove an extension
DROP EXTENSION '<name>' FOR <table>;

Beacon parses the payload strictly. It rejects an unknown key and an invalid value. It does not ignore them. A spelling error therefore gives an error. It does not switch the feature off in silence.

The preset extension

A preset is a named filter set on the table. A preset gives a caller a short name for a common query. The caller picks shallow instead of the full filter.

SET EXTENSION 'preset' FOR obs TO '{
  "presets": [
    {
      "name": "shallow",
      "description": "Surface layer only",
      "filters": [{"column": "depth", "op": "<=", "value": 10}]
    },
    {
      "name": "north_atlantic",
      "description": "North Atlantic basin",
      "filters": [
        {"column": "lat", "op": ">=", "value": 0},
        {"column": "lat", "op": "<=", "value": 70}
      ]
    }
  ]
}';

Each preset has a name, a description and a list of filters. The description says what the preset selects. A filter is {"column", "op", "value"}. Beacon combines the filters of one preset with AND.

See also

• External Tables: register the tables that take an extension.
• Access control: the identity and role grants that control what an agent reads.