Mutation and update cache

Now let's do the integration part. Open components/Todo/TodoItem.js and add the following code to define the delete mutation

components/Todo/TodoItem.js

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const TodoItem = ({index, todo, client}) => {

+  const REMOVE_TODO = gql`
+    mutation removeTodo ($id: Int!) {
+      delete_todos(where: {id: {_eq: $id}}) {
+        affected_rows
+      }
+    }
+  `;

+  const [removeTodoMutation] = useMutation(REMOVE_TODO);

We have a function defined to handle the button click to remove a todo. Let's update the function to use removeTodoMutation mutate function.

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  const removeTodo = (e) => {
    e.preventDefault();
    e.stopPropagation();
+   removeTodoMutation({
+     variables: {id: todo.id},
+     optimisticResponse: true,
+     update: (cache) => {
+       const existingTodos = cache.readQuery({ query: GET_MY_TODOS });
+       const newTodos = existingTodos.todos.filter(t => (t.id !== todo.id));
+       cache.writeQuery({
+         query: GET_MY_TODOS,
+         data: {todos: newTodos}
+       });
+     }
+   });
  };