Sign up for Hasura Newsletter
Loading...

Fetch and Sync Public Todos - Live Notifications

Let's write some code that will:

  • Fetch the last N number of public todos
  • Listen for new public todos to be created, realtime
  • Push new todos into a queue of received todos, which we can display by clicking a button
  • Allow us to ask for the next N older todos

Open src/components/TodoPublicList.vue and add the following:

githubsrc/components/TodoPublicList.vue
<script setup lang="ts">
import TodoItem from "../components/TodoItem.vue"
- import { reactive } from "vue"
+ import { computed, reactive } from "vue"
+ import { useSubscription } from "@vue/apollo-composable"
const { type } = defineProps({ type: String })
+ const SUBSCRIPTION_TODOS_WITH_USER = gql`
+ subscription todos_with_user(
+ $where: todos_bool_exp!
+ $order_by: [todos_order_by!]
+ $limit: Int = 10
+ $offset: Int
+ ) {
+ todos(where: $where, order_by: $order_by, limit: $limit, offset: $offset) {
+ id
+ title
+ is_completed
+ created_at
+ is_public
+ user {
+ id
+ name
+ }
+ }
+ }
+ `
+ const { onResult } = useSubscription(
+ SUBSCRIPTION_TODOS_WITH_USER,
+ computed(() => ({
+ limit: state.limit,
+ where: {
+ is_public: { _eq: true },
+ },
+ order_by: {
+ created_at: "desc",
+ },
+ }))
+ )
+ onResult(({ data }) => {
+ // If this is the first subscription result and we've not loaded initial todos
+ // Then we should just set the initial state.todos value and stop
+ if (!initialTodosSet) {
+ state.todos = data.todos
+ initialTodosSet = true
+ } else {
+ // Else, if the change is because of a change in the "limit" value (due to the "load more" button being clicked)
+ // Then we should add the new todos to the existing todos and clear the "receivedTodos" array
+ if (state.limit != previousLimit) {
+ state.todos = [...data.todos, ...state.receivedTodos]
+ state.receivedTodos = []
+ previousLimit = state.limit
+ } else {
+ // Else, if the change is because of a new todo being created
+ state.receivedTodos.push(data.todos[0])
+ }
+ }
+ })
const state = reactive({
limit: 5,
type: "public",
+ receivedTodos: [],
+ todos: [],
- todos: [
- {
- id: "1",
- title: "This is public todo 1",
- is_public: true,
- user: {
- name: "someUser1",
- },
- },
- {
- id: "2",
- title: "This is public todo 2",
- is_completed: false,
- is_public: true,
- user: {
- name: "someUser2",
- },
- },
- {
- id: "3",
- title: "This is public todo 3",
- is_public: true,
- user: {
- name: "someUser3",
- },
- },
- {
- id: "4",
- title: "This is public todo 4",
- is_public: true,
- user: {
- name: "someUser4",
- },
- },
- ],
})
function loadMoreClicked() {
+ state.todos = [...state.receivedTodos, ...state.todos]
+ state.receivedTodos = []
}
function loadOlderClicked() {
+ state.limit += 5
}
</script>

What does the Subscription do?

The subscription fetches todos with a simple condition; is_public must be true. It is also a computed subscription, this is because we want it to be reactive. We need the reactivity so that we can model the following logic:

  • If state.todos is empty and hasn't been set, then run a subscription with the variables:
{
where: {
is_public: { _eq: true },
}
}
  • After state.todos has a value set, instead modify and re-start the subscription to watch for ID's created that are greater than the most recent todo's ID. This powers the realtime todo-received notification:
{
where: {
is_public: { _eq: true },
id: { _gte: state.todos[0].id }
}
}
Did you find this page helpful?
Start with GraphQL on Hasura for Free
  • ArrowBuild apps and APIs 10x faster
  • ArrowBuilt-in authorization and caching
  • Arrow8x more performant than hand-rolled APIs
Promo
footer illustration
Brand logo
© 2022 Hasura Inc. All rights reserved
Github
Titter
Discord
Facebook
Instagram
Youtube
Linkedin