Registries: how Odoo finds the code you added

Your module is loaded, but nothing calls it. The registry is how Odoo discovers what you added.

import { registry } from "@web/core/registry";

registry.category("systray").add("my_module.clock", { Component: Clock });

It is a map of named sub-maps. Odoo reads them when it needs the things inside.

The categories you will use

Category	Holds	Covered in
services	Services	Next lesson
fields	Field widgets	Part 6
views	View types	Part 6
actions	Client actions	Part 6
systray	Top right icons	Part 1
main_components	Components mounted at the root	Below
user_menuitems	Items in the user dropdown
favoriteMenu	Items in the search Favourites menu
formatters / parsers	Value display and input
view_widgets	<widget> tags inside a view
error_handlers	Handling specific server errors
error_dialogs	Dialog per error type
command_provider	Entries in the command palette
cogMenu	Items in the cog menu of a view

add, and its options

registry.category("systray").add(
    "my_module.clock",         // key, namespace it
    { Component: Clock },      // value, shape depends on the category
    { sequence: 10, force: true },
);

The key must be unique within the category. Prefix it with your module name. Two modules both adding clock is a real collision, and the failure is one module silently not appearing.

sequence orders entries. Lower comes first. Categories that care about order read it; others ignore it.

force: true replaces an existing key instead of throwing. Without it, adding a key that exists is an error. Use force deliberately: it means overriding another module, and if that module is reinstalled or reordered the result depends on load order.

Reading and reacting

const systray = registry.category("systray");

systray.get("my_module.clock");          // throws if absent
systray.get("my_module.clock", null);    // default if absent
systray.contains("my_module.clock");     // boolean
systray.getAll();                        // values, sequence ordered
systray.getEntries();                    // [key, value] pairs
systray.remove("my_module.clock");

Registries emit events, which is how the client picks up something added after boot:

registry.category("services").addEventListener("UPDATE", (ev) => {
    console.log("service registry changed", ev.detail);
});

You rarely need this. It matters when something registers lazily.

main_components

For a component that must exist on screen regardless of the current view: a global banner, an overlay, a connection indicator.

import { registry } from "@web/core/registry";
import { OfflineBanner } from "./offline_banner";

registry.category("main_components").add("my_module.offline_banner", {
    Component: OfflineBanner,
    props: {},
});

Mounted once at the root, outside the action manager, so it survives navigation. Keep these few and keep them cheap: they render for every user on every page.

Registering at module scope

// Runs when the file loads
registry.category("systray").add("my_module.clock", { Component: Clock });

This is the normal pattern and it is fine. The caveat is doing anything beyond registering at module scope. Do not read a registry at module scope, because whether the entry you want is there depends on bundle order:

// Fragile
const existing = registry.category("fields").get("char");

Read it inside setup or a function, by which time everything has loaded.

Inspecting at runtime

In developer mode, in the console:

odoo.loader.modules.get("@web/core/registry").registry.category("fields").getEntries()

That lists every registered field widget with its key. It is the fastest way to find the exact name of a widget you want to extend, and to confirm your own registration actually happened.

Shorter, if you are inside a component in the debugger:

odoo.__WOWL_DEBUG__.root.env.services

When registering silently does nothing

Three causes, in order.

The file never loaded. Check it:

Object.keys(odoo.loader.modules).filter(m => m.includes("my_module"))

Nothing listed means a bundle problem. Back to Part 1.

The key already existed and threw. Look for the error at boot. It appears early and scrolls away.

Wrong category name. registry.category("systrays") creates a new, empty category called systrays rather than erroring. Nothing reads it, nothing complains, nothing appears. Spelling matters and there is no safety net.

What is next

Writing a service of your own, which is where shared state and shared behaviour belong.