Composing Stores

Composing stores is about having stores that use each other, and this is supported in Pinia. There is one rule to follow:

If two or more stores use each other, they cannot create an infinite loop through getters or actions. They cannot both directly read each other state in their setup function:

const useX = defineStore('x', () => {
  const y = useY()

  // ❌ This is not possible because y also tries to read x.name
  y.name

  function doSomething() {
    // ✅ Read y properties in computed or actions
    const yName = y.name
    // ...
  }

  return {
    name: ref('I am X'),
  }
})

const useY = defineStore('y', () => {
  const x = useX()

  // ❌ This is not possible because x also tries to read y.name
  x.name

  function doSomething() {
    // ✅ Read x properties in computed or actions
    const xName = x.name
    // ...
  }

  return {
    name: ref('I am Y'),
  }
})

Nested Stores

Note that if one store uses another store, you can directly import and call the useStore() function within actions and getters. Then you can interact with the store just like you would from within a Vue component. See Shared Getters and Shared Actions.

When it comes to setup stores, you can simply use one of the stores at the top of the store function:

import { useUserStore } from './user'

export const useCartStore = defineStore('cart', () => {
  const user = useUserStore()
  const list = ref([])

  const summary = computed(() => {
    return `Hi ${user.name}, you have ${list.value.length} items in your cart. It costs ${price.value}.`
  })

  function purchase() {
    return apiPurchase(user.id, this.list)
  }

  return { summary, purchase }
})

Shared Getters

You can simply call useUserStore() inside a getter:

import { defineStore } from 'pinia'
import { useUserStore } from './user'

export const useCartStore = defineStore('cart', {
  getters: {
    summary(state) {
      const user = useUserStore()

      return `Hi ${user.name}, you have ${state.list.length} items in your cart. It costs ${state.price}.`
    },
  },
})

Shared Actions

The same applies to actions:

import { defineStore } from 'pinia'
import { useUserStore } from './user'

export const useCartStore = defineStore('cart', {
  actions: {
    async orderCart() {
      const user = useUserStore()

      try {
        await apiOrderCart(user.token, this.items)
        // another action
        this.emptyCart()
      } catch (err) {
        displayError(err)
      }
    },
  },
})

Since actions can be asynchronous, make sure all of your useStore() calls appear before any await. Otherwise, this could lead to using the wrong pinia instance in SSR apps:

import { defineStore } from 'pinia'
import { useUserStore } from './user'

export const useCartStore = defineStore('cart', {
  actions: {
    async orderCart() {
      // ✅ call at the top of the action before any `await`
      const user = useUserStore()

      try {
        await apiOrderCart(user.token, this.items)
        // ❌ called after an `await` statement
        const otherStore = useOtherStore()
        // another action
        this.emptyCart()
      } catch (err) {
        displayError(err)
      }
    },
  },
})