Mutation and update cache

Now let's do the integration part. Open src/components/TodoItem.vue and add the following code below:

src/components/TodoItem.vue

<script>
+ import gql from 'graphql-tag';
  export default {
    ...
  }
</script>

Let's define the graphql mutation to update the completed status of the todo

<script>
  import gql from 'graphql-tag';
+ const TOGGLE_TODO = gql`
+   mutation update_todos($id: Int!, $isCompleted: Boolean!) {
+    update_todos(where: { id: { _eq: $id } }, _set: { is_completed: $isCompleted }) {
+       affected_rows
+     }
+   }
+ `;
  export default {
    ...
  }
</script>

We need to call this.$apollo.mutate to make the mutation.

  export default {
    props: ['todos', 'type'],
    methods: {
      handleTodoToggle: function (todo) {
        // update todo data in db here
+       this.$apollo.mutate({
+         mutation: TOGGLE_TODO,
+         variables: {
+          id: todo.id,
+          isCompleted: !todo.is_completed
+         },
+         update: (store, { data: { update_todos } }) => {
+           if (update_todos.affected_rows) {
+             // eslint-disable-next-line
+             console.log(update_todos);
+           }
+         },
+       });
     },

The above code will just make a mutation, updating the todo's is_completed property in the database. To update the cache, we will be using the update function again to modify the cache. We need to fetch the current list of todos from the cache before modifying it. So let's import the query.

<script>
  import gql from 'graphql-tag';
+ import { GET_MY_TODOS } from "./TodoPrivateList.vue";
  const TOGGLE_TODO = gql`
    mutation update_todos($id: Int!, $isCompleted: Boolean!) {
      update_todos(where: { id: { _eq: $id } }, _set: { is_completed: $isCompleted }) {
        affected_rows
      }
    }
  `;

Now let's add the code for update function.

  methods: {
    handleTodoToggle: function (todo) { // eslint-disable-line
      // update todo data in db here
      this.$apollo.mutate({
        mutation: TOGGLE_TODO,
        variables: {
         id: todo.id,
         isCompleted: !todo.is_completed
        },
        update: (store, { data: { update_todos } }) => {
          if (update_todos.affected_rows) {
-           // eslint-disable-next-line
-           console.log(update_todos);
+           if (this.type === "private") {
+             // Read the data from our cache for this query.
+             const data = store.readQuery({
+               query: GET_MY_TODOS,
+             });
+             const toggledTodo = data.todos.find(t => t.id === todo.id);
+             toggledTodo.is_completed = !todo.is_completed;
+             store.writeQuery({
+               query: GET_MY_TODOS,
+               data
+             });
+           } 
          }
        },
      });
    },

We are fetching the existing todos from the cache using cache.readQuery and updating the is_completed value for the todo that has been updated.

Finally we are writing the updated todo list to the cache using cache.writeQuery.

Optimistic response

Now let's remove the input lag by adding optimisticResponse. This adds a fake result as soon as the network request is made so that the UI can render quickly.

  handleTodoToggle: function (todo) { // eslint-disable-line
    // update todo data in db here
    this.$apollo.mutate({
      mutation: TOGGLE_TODO,
      variables: {
       id: todo.id,
       isCompleted: !todo.is_completed
      },
      update: (store, { data: { update_todos } }) => {
        if (update_todos.affected_rows) {
          if (this.type === "private") {
            // Read the data from our cache for this query.
            const data = store.readQuery({
              query: GET_MY_TODOS,
            });
            const toggledTodo = data.todos.find(t => t.id === todo.id);
            toggledTodo.is_completed = !todo.is_completed;
            store.writeQuery({
              query: GET_MY_TODOS,
              data
            });
          } 
        }
      },
+     optimisticResponse: {
+       __typename: 'Mutation',
+       update_todos: {
+         __typename: 'todos',
+         id: todo.id,
+         is_completed: !todo.is_completed,
+         affected_rows: 1
+       },
+     }
    });
  },

Now the fake result should appear quickly in case the network request takes more time. This should trigger a call to update function which will update the todo temporarily till the actual response from the server is received.

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