wasp/web/docs/tutorial/06-actions.md

---
title: 6. Modifying Data
---

import useBaseUrl from '@docusaurus/useBaseUrl';
import { ShowForTs, ShowForJs } from '@site/src/components/TsJsHelpers';
import Collapse from '@site/src/components/Collapse';

In the previous section, we learned about using queries to fetch data and only briefly mentioned that actions can be used to update the database. Let's learn more about actions so we can add and update tasks in the database.

We have to create:

1. A Wasp action that creates a new task.
2. A React form that calls that action when the user creates a task.

## Creating a New Action

Creating an action is very similar to creating a query.

### Declaring an Action

We must first declare the action in `main.wasp`:

<Tabs groupId="js-ts">
<TabItem value="js" label="JavaScript">

```wasp title="main.wasp"
// ...

action createTask {
  fn: import { createTask } from "@server/actions.js",
  entities: [Task]
}
```

</TabItem>
<TabItem value="ts" label="TypeScript">

```wasp title="main.wasp"
// ...

action createTask {
  fn: import { createTask } from "@server/actions.js",
  entities: [Task]
}
```

</TabItem>
</Tabs>

### Implementing an Action

Let's now define a <ShowForJs>JavaScript</ShowForJs><ShowForTs>TypeScript</ShowForTs> function for our `createTask` action:

<Tabs groupId="js-ts">
<TabItem value="js" label="JavaScript">

```js title="src/server/actions.js"
export const createTask = async (args, context) => {
  return context.entities.Task.create({
    data: { description: args.description },
  })
}
```

</TabItem>
<TabItem value="ts" label="TypeScript">

```ts title="src/server/actions.ts"
import { Task } from '@wasp/entities'
import { CreateTask } from '@wasp/actions/types'

type CreateTaskPayload = Pick<Task, 'description'>

export const createTask: CreateTask<CreateTaskPayload, Task> = async (
  args,
  context
) => {
  return context.entities.Task.create({
    data: { description: args.description },
  })
}
```

Once again, we've annotated the action with the generated `CreateTask` and `Task` types generated by Wasp. Just like with queries, defining the types on the implemention makes them available on the frontend, giving us **full-stack type safety**.

</TabItem>
</Tabs>

:::tip
We put the function in a new file `src/server/actions.{js,ts}`, but we could have put it anywhere we wanted! There are no limitations here, as long as the declaration in the Wasp file imports it correctly and the file is located within `src/server`.
:::

## Invoking the Action on the Client

First, let's define a form that the user can create new tasks with.

<Tabs groupId="js-ts">
<TabItem value="js" label="JavaScript">

```jsx {2,7-26} title="src/client/MainPage.jsx"
import getTasks from '@wasp/queries/getTasks'
import createTask from '@wasp/actions/createTask'
import { useQuery } from '@wasp/queries'

// ...

const NewTaskForm = () => {
  const handleSubmit = async (event) => {
    event.preventDefault()
    try {
      const target = event.target
      const description = target.description.value
      target.reset()
      await createTask({ description })
    } catch (err) {
      window.alert('Error: ' + err.message)
    }
  }

  return (
    <form onSubmit={handleSubmit}>
      <input name="description" type="text" defaultValue="" />
      <input type="submit" value="Create task" />
    </form>
  )
}
```

</TabItem>
<TabItem value="ts" label="TypeScript">

```tsx {1,3,9-28} title="src/client/MainPage.tsx"
import { FormEvent } from 'react'
import getTasks from '@wasp/queries/getTasks'
import createTask from '@wasp/actions/createTask'
import { useQuery } from '@wasp/queries'
import { Task } from '@wasp/entities'

// ...

const NewTaskForm = () => {
  const handleSubmit = async (event: FormEvent<HTMLFormElement>) => {
    event.preventDefault()
    try {
      const target = event.target as HTMLFormElement
      const description = target.description.value
      target.reset()
      await createTask({ description })
    } catch (err: any) {
      window.alert('Error: ' + err.message)
    }
  }

  return (
    <form onSubmit={handleSubmit}>
      <input name="description" type="text" defaultValue="" />
      <input type="submit" value="Create task" />
    </form>
  )
}
```

</TabItem>
</Tabs>

Unlike queries, you call actions directly (i.e., without wrapping it with a hook) because we don't need reactivity. The rest is just regular React code.

<ShowForTs>

Finally, because we've previously annotated the Action's backend implementation with the correct type, Wasp knows that the `createTask` action expects a value of type `{ description: string }` (try changing the argument and reading the error message). Wasp also knows that a call to the `createTask` action returns a `Task` but are not using it in this example.

</ShowForTs>

Now, we just need to add this form to the page component:

<Tabs groupId="js-ts">
<TabItem value="js" label="JavaScript">

```jsx {10} title="src/client/MainPage.tsx"
import getTasks from '@wasp/queries/getTasks'
import createTask from '@wasp/actions/createTask'
import { useQuery } from '@wasp/queries'

const MainPage = () => {
  const { data: tasks, isLoading, error } = useQuery(getTasks)

  return (
    <div>
      <NewTaskForm />

      {tasks && <TasksList tasks={tasks} />}

      {isLoading && 'Loading...'}
      {error && 'Error: ' + error}
    </div>
  )
}
```

</TabItem>
<TabItem value="ts" label="TypeScript">

```tsx {12} title="src/client/MainPage.tsx"
import { FormEvent } from 'react'
import getTasks from '@wasp/queries/getTasks'
import createTask from '@wasp/actions/createTask'
import { useQuery } from '@wasp/queries'
import { Task } from '@wasp/entities'

const MainPage = () => {
  const { data: tasks, isLoading, error } = useQuery(getTasks)

  return (
    <div>
      <NewTaskForm />

      {tasks && <TasksList tasks={tasks} />}

      {isLoading && 'Loading...'}
      {error && 'Error: ' + error}
    </div>
  )
}
```

</TabItem>
</Tabs>

And now we have a form that creates new tasks.

Try creating a "Build a Todo App in Wasp" task and see it appear in the list below. The task is created on the server and saved in the database.

Try refreshing the page or opening it in another browser, you'll see the tasks are still there!

<img alt="Todo App - creating new task"
src={useBaseUrl('img/todo-app-new-task.png')}
style={{ border: "1px solid black" }}
/>
<br />
<br />

:::note Automatic Query Invalidation
When you create a new task, the list of tasks is automatically updated to display the new task, even though we have not written any code that would do that! These automatic updates are handled by code that Wasp generates.

When you declared the `getTasks` and `createTask` operations, you specified that they both use the `Task` entity. So when `createTask` is called, Wasp knows that the data `getTasks` fetches may have changed and automatically updates it in the background. This means that **out of the box, Wasp will make sure that all your queries are kept in-sync with changes made by any actions**.

This behavior is convenient as a default but can cause poor performance in large apps. While there is no mechanism for overriding this behavior yet, it is something that we plan to include in Wasp in the future. This feature is tracked [here](https://github.com/wasp-lang/wasp/issues/63).
:::

## A Second Action

Our Todo app isn't finished if you can't mark a task as done! We'll create a new action to update a task's status and call it from React whenever a task's checkbox is toggled.

Since we've already created one task together, try to create this one yourself. It should be an action named `updateTask` that takes a task `id` and an `isDone` in its arguments. You can check our implementation below.

<Collapse title="Solution">

The action declaration:

<Tabs groupId="js-ts">
<TabItem value="js" label="JavaScript">

```wasp title="main.wasp"
// ...

action updateTask {
  fn: import { updateTask } from "@server/actions.js",
  entities: [Task]
}
```

</TabItem>
<TabItem value="ts" label="TypeScript">

```wasp title="main.wasp"
// ...

action updateTask {
  fn: import { updateTask } from "@server/actions.js",
  entities: [Task]
}
```

</TabItem>
</Tabs>

The implementation on the server:

<Tabs groupId="js-ts">
<TabItem value="js" label="JavaScript">

```js title="src/server/actions.js"
// ...

export const updateTask = async ({ id, isDone }, context) => {
  return context.entities.Task.update({
    where: { id },
    data: {
      isDone: isDone,
    },
  })
}
```

</TabItem>
<TabItem value="ts" label="TypeScript">

```ts title="src/server/actions.ts"
// highlight-next-line
import { CreateTask, UpdateTask } from '@wasp/actions/types'

// ...

type UpdateTaskPayload = Pick<Task, 'id' | 'isDone'>

export const updateTask: UpdateTask<UpdateTaskPayload, Task> = async (
  { id, isDone },
  context
) => {
  return context.entities.Task.update({
    where: { id },
    data: {
      isDone: isDone,
    },
  })
}
```

</TabItem>
</Tabs>

</Collapse>

Now, we can call `updateTask` from the React component:

<Tabs groupId="js-ts">
<TabItem value="js" label="JavaScript">

```jsx {2,7-16,24} title="src/client/MainPage.jsx"
// ...
import updateTask from '@wasp/actions/updateTask'

// ...

const Task = ({ task }) => {
  const handleIsDoneChange = async (event) => {
    try {
      await updateTask({
        id: task.id,
        isDone: event.target.checked,
      })
    } catch (error) {
      window.alert('Error while updating task: ' + error.message)
    }
  }

  return (
    <div>
      <input
        type="checkbox"
        id={String(task.id)}
        checked={task.isDone}
        onChange={handleIsDoneChange}
      />
      {task.description}
    </div>
  )
}
// ...
```

</TabItem>
<TabItem value="ts" label="TypeScript">

```tsx {2,4,9-18,26} title="src/client/MainPage.tsx"
// ...
import { FormEvent, ChangeEvent } from 'react'
// ...
import updateTask from '@wasp/actions/updateTask'

// ...

const Task = ({ task }: { task: Task }) => {
  const handleIsDoneChange = async (event: ChangeEvent<HTMLInputElement>) => {
    try {
      await updateTask({
        id: task.id,
        isDone: event.target.checked,
      })
    } catch (error: any) {
      window.alert('Error while updating task: ' + error.message)
    }
  }

  return (
    <div>
      <input
        type="checkbox"
        id={String(task.id)}
        checked={task.isDone}
        onChange={handleIsDoneChange}
      />
      {task.description}
    </div>
  )
}
// ...
```

</TabItem>
</Tabs>

Awesome! Now we can check off this task 🙃 Let's add one more interesting feature to our app.