Business logic in any language. One kernel.

import { Kernable, Rejected, domain } from "@kernable/sdk";

const cart = domain("shop").aggregate("cart", { items: 0, checkedOut: false });

cart.apply("ItemAdded", (state, data: { qty: number }) => { state.items += data.qty; });
cart.apply("CheckedOut", (state) => { state.checkedOut = true; });

cart.command("AddItem", (state, data: { sku: string; qty: number }) => {
  if (state.checkedOut) throw new Rejected("Cart is checked out");
  return [{ type: "ItemAdded", data }];
});

cart.command("CheckOut", (state, _data, _cmd, ctx) => {
  if (state.items === 0) throw new Rejected("Cart is empty");
  // ctx.now() and ctx.id() stay the same if the command runs again.
  return [{ type: "CheckedOut", data: { at: ctx.now().toISOString(), orderId: ctx.id() } }];
});

await new Kernable({ key: "app.key" }).worker(cart).run();

import { Kernable, Rejected, domain } from "@kernable/sdk";

const carts = domain("shop").readModel("carts");
const rows = new Map<string, { items: number; order?: string }>();

carts.on("ItemAdded", (data: { qty: number }, evt) => {
  const row = rows.get(evt.aggregateId) ?? { items: 0 };
  row.items += data.qty;
  rows.set(evt.aggregateId, row);
});

carts.on("CheckedOut", (data: { orderId: string }, evt) => {
  rows.get(evt.aggregateId)!.order = data.orderId;
});

carts.query("GetCart", (data: { id: string }) => {
  const row = rows.get(data.id);
  if (!row) throw new Rejected("no such cart", "not_found");
  return row;
});

await new Kernable({ key: "app.key" }).listener(carts).run();

import { Kernable } from "@kernable/sdk";

const kernable = new Kernable({ key: "app.key" });
const cartC1 = { domain: "shop", aggregateType: "cart", aggregateId: "c1" };

await kernable.submit({ ...cartC1, type: "AddItem", data: { sku: "apple", qty: 2 } });
// submit returned only after every listener processed the event: no polling needed.
let cart = await kernable.query({ domain: "shop", type: "GetCart", data: { id: "c1" } });
// { items: 2 }

await kernable.submit({ ...cartC1, type: "CheckOut" });
const outcome = await kernable.submit({ ...cartC1, type: "AddItem", data: { sku: "pear", qty: 1 } });
// { committed: false, code: "rejected", message: "Cart is checked out" }