Mutation and update cache

Now let's do the integration part. Open src/app/Todo/TodoItem.ts and add the following code below the other imports:

+ import { Apollo, gql } from 'apollo-angular';

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

src/app/Todo/TodoItem.ts

import { Component, Input } from '@angular/core';
import { Apollo, gql } from 'apollo-angular';

+  const TOGGLE_TODO = gql`
+    mutation toggleTodo ($id: Int!, $isCompleted: Boolean!) {
+      update_todos(where: {id: {_eq: $id}}, _set: {is_completed: $isCompleted}) {
+        affected_rows
+      }
+    }
+  `;

Apollo apollo.mutate

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

  import { Component, Input } from '@angular/core';
+ import { Apollo,gql } from 'apollo-angular';

  export class TodoItem {
    @Input() todo: any;

+   constructor(private apollo: Apollo) {}
    ...
  }

We already have the onChange handler toggleTodo for the input. Let's update the function to make a mutation.

  const toggleTodo = () => {
+    this.apollo.mutate({
+          mutation: TOGGLE_TODO,
+          variables: {id: this.todo.id, isCompleted: !this.todo.is_completed},
+        }).subscribe(({ data }) => {
+          console.log('got data', data);
+        },(error) => {
+          console.log('there was an error sending the query', error);
+        });
+      };

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.

+ import { GET_MY_TODOS } from './TodoPrivateList';

Now let's add the code for update function.

  toggleTodo() {
    this.apollo.mutate({
      mutation: TOGGLE_TODO,
      variables: { id: this.todo.id, isCompleted: !this.todo.is_completed },
+       update: (cache) => {
+          const existingTodos : any = cache.readQuery({ query: GET_MY_TODOS });
+          const newTodos = existingTodos.todos.map(t => {
+            if (t.id === this.todo.id) {
+              return { ...t, is_completed: !t.is_completed };
+            } else {
+              return t;
+            }
+          });
+          cache.writeQuery({
+            query: GET_MY_TODOS,
+            data: {todos: newTodos}
+          });
+        },
    }).subscribe(({ data }) => {
      console.log('got data', data);
    },(error) => {
      console.log('there was an error sending the query', error);
    });
  }