Make an instance available
A library instance is registered under its key-type path, such as ["user"] or ["address","user"], plus optional scopes.
Composition / @fjell/registry
Why does the registry exist?
Because an application has more than one Item instance. The registry gives Fjell a shared place to name, create, register, and find the right User, Address, Company, Team, and Membership services by coordinate and scope.
It is the framework's directory.
Imagine a large application with separate operations for Users, Companies, Addresses, Teams, and Team memberships—and sometimes multiple implementations of the same coordinate for different scopes or databases. Passing every instance manually through every constructor becomes fragile. The registry centralizes discovery.
Find the matching instance
Callers ask for the coordinate and scope they need. The registry returns the matching instance or a clear miss.
Resolve the right level
User and Company are primary coordinates. Address and Membership coordinates include their parent type, preserving the graph's hierarchy.
Connect without hard-wiring
Lib, routers, and adapters can discover neighbors through the registry instead of importing concrete implementations everywhere.
What it looks up.
User
PItem operations
[user]PItem operations
↔
Company
PItem operations
[company]PItem operations
Address
CItem operations
[address,user]CItem operations
↔
Membership
role-aware child
[membership,team]role-aware child
The registry does not store Alex's data. It stores the services/instances that know how to operate on each Item coordinate.
Why not just import everything?
Direct imports couple the HTTP layer to a specific storage implementation, make alternate scopes awkward, and make circular dependencies more likely. A registry provides an explicit composition boundary. It also gives Fjell one place to instrument lookups and understand which coordinate is being requested.
const registry = createRegistry("application");
const users = registry.createInstance(
["user"],
userCoordinate,
userFactory,
{ scopes: ["postgres"] }
);
const addresses = registry.createInstance(
["address", "user"],
addressCoordinate,
addressFactory,
{ scopes: ["postgres"] }
);
const userService = registry.get(["user"], { scopes: ["postgres"] });The registry's place in the story.
Core defines coordinates and operation contracts. The registry composes instances built on those contracts. Lib uses that composition point to build domain libraries, and routers/adapters consume the resulting instances.
Previous: core →Next: lib →Return to the graph →