feat: expose providePinia to use multiple root stores

packages/pinia/__tests__/multipleRoots.spec.ts

@@ -0,0 +1,98 @@
+import { createPinia, defineStore, providePinia } from '../src'
+import { mount } from '@vue/test-utils'
+import { defineComponent } from 'vue'
+
+describe('Multiple Roots', () => {
+  function defineMyStore() {
+    return defineStore({
+      id: 'main',
+      state: () => ({
+        n: 0,
+      }),
+    })
+  }
+
+  it('uses the same root in child components by default', () => {
+    expect.assertions(2)
+    const pinia = createPinia()
+    const useStore = defineMyStore()
+
+    const ChildComponent = defineComponent({
+      template: 'no',
+      setup() {
+        const store = useStore()
+        expect(store.n).toBe(1)
+      },
+    })
+
+    mount(
+      {
+        template: '<ChildComponent />',
+        components: { ChildComponent },
+        setup() {
+          const store = useStore()
+          expect(store.n).toBe(0)
+          store.n++
+        },
+      },
+      { global: { plugins: [pinia] } }
+    )
+  })
+
+  it('can use a new pinia root for all child components', async () => {
+    expect.assertions(2)
+    const pinia = createPinia()
+    const useStore = defineMyStore()
+
+    const ChildComponent = defineComponent({
+      template: 'no',
+      setup() {
+        const store = useStore()
+        expect(store.n).toBe(0)
+      },
+    })
+    mount(
+      {
+        template: '<ChildComponent />',
+        components: { ChildComponent },
+        setup() {
+          providePinia(createPinia())
+          const store = useStore()
+          expect(store.n).toBe(0)
+          store.n++
+        },
+      },
+      { global: { plugins: [pinia] } }
+    )
+  })
+
+  it('state is shared between child components', async () => {
+    expect.assertions(3)
+    const pinia = createPinia()
+    const useStore = defineMyStore()
+
+    const ChildComponent = defineComponent({
+      template: 'no',
+      props: { counter: { type: Number, required: true } },
+      setup(props: { counter: number }) {
+        const store = useStore()
+        expect(store.n).toBe(props.counter)
+        store.n++
+      },
+    })
+    mount(
+      {
+        template:
+          '<ChildComponent :counter="0" /><ChildComponent :counter="1" />',
+        components: { ChildComponent },
+        setup() {
+          const store = useStore()
+          expect(store.n).toBe(0)
+          store.n++
+          providePinia(createPinia())
+        },
+      },
+      { global: { plugins: [pinia] } }
+    )
+  })
+})

packages/pinia/src/index.ts

@@ -1,7 +1,7 @@
 /**
  * @module pinia
  */
-export { setActivePinia, getActivePinia } from './rootStore'
+export { setActivePinia, getActivePinia, providePinia } from './rootStore'
 export { createPinia } from './createPinia'
 export type {
   Pinia,

packages/pinia/src/rootStore.ts

@@ -4,6 +4,7 @@ import {
   getCurrentInstance,
   inject,
   InjectionKey,
+  provide,
   Ref,
 } from 'vue-demi'
 import {
@@ -97,6 +98,13 @@ export const piniaSymbol = (
   __DEV__ ? Symbol('pinia') : /* istanbul ignore next */ Symbol()
 ) as InjectionKey<Pinia>
 
+/**
+ * Define which pinia to use in all child components.
+ */
+export function providePinia(pinia: Pinia) {
+  provide(piniaSymbol, pinia)
+}
+
 /**
  * Context argument passed to Pinia plugins.
  */