5. Querying the Database

We want to know which tasks we need to do, so let's list them! The primary way of interacting with entities in Wasp is by using queries and actions, collectively known as operations.

Queries are used to read an entity, while actions are used to create, modify, and delete entities. Since we want to list the tasks, we'll want to use a query.

To list tasks we have to:

1. Create a query that fetches tasks from the database.
2. Update the MainPage.tsx to use that query and display the results.

Defining the Query

We'll create a new query called getTasks. We'll need to declare the query in the Wasp file and write its implementation in .

Declaring a Query

We need to add a query declaration to main.wasp so that Wasp knows it exists:

JavaScript

main.wasp

// ...

query getTasks {
  // Specifies where the implementation for the query function is.
  // Use `@server` to import files inside the `src/server` folder.
  fn: import { getTasks } from "@server/queries.js",
  // Tell Wasp that this query reads from the `Task` entity. By doing this, Wasp
  // will automatically update the results of this query when tasks are modified.
  entities: [Task]
}

TypeScript

main.wasp

// ...

query getTasks {
  // Specifies where the implementation for the query function is.
  // Use `@server` to import files inside the `src/server` folder.
  fn: import { getTasks } from "@server/queries.js",
  // Tell Wasp that this query reads from the `Task` entity. By doing this, Wasp
  // will automatically update the results of this query when tasks are modified.
  entities: [Task]
}

Importing Typescript files

Even though you are using TypeScript and plan to implement this query in src/server/queries.ts, you still need to import it using a .js extension. Wasp internally uses esnext module resolution, which requires importing all files with a .js extension. This is only needed when importing @server@ files.

Read more about ES modules in TypeScript here. If you're interested in the discussion and the reasoning behind this, read about it in this GitHub issue.

Implementing a Query

JavaScript

src/server/queries.js

export const getTasks = async (args, context) => {
  return context.entities.Task.findMany({
    orderBy: { id: 'asc' },
  })
}

TypeScript

src/server/queries.ts

import { Task } from '@wasp/entities'
import { GetTasks } from '@wasp/queries/types'

export const getTasks: GetTasks<void, Task[]> = async (args, context) => {
  return context.entities.Task.findMany({
    orderBy: { id: 'asc' },
  })
}

Wasp automatically generates the types GetTasks and Task based the contents of main.wasp:

• Task is a type corresponding to the Task entity we've defined in main.wasp.
• GetTasks is a generic type Wasp automatically generated based the getTasks query we've defined in main.wasp.

You can use these types to specify the Query's input and output types. This query doesn't expect any arguments (its input type is void), but it does return an array of tasks (its output type is Task[]).

Annotating the queries is optional, but highly recommended because doing so enables full-stack type safety. We'll see what this means in the next step.

Query function parameters:

• args: object, arguments the query is given by the caller.
• context: object, information provided by Wasp.

Since we declared in main.wasp that our query uses the Task entity, Wasp injected a Prisma client for the Task entity as context.entities.Task - we used it above to fetch all the tasks from the database.

info

Queries and actions are NodeJS functions that are executed on the server. Therefore, we put them in the src/server folder.

Invoking the Query On the Frontend

While we implement queries on the server, Wasp generates client-side functions that automatically takes care of serialization, network calls, and chache invalidation, allowing you to call the server code like it's a regular function. This makes it easy for us to use the getTasks query we just created in our React component:

JavaScript

src/client/MainPage.jsx

import getTasks from '@wasp/queries/getTasks'
import { useQuery } from '@wasp/queries'

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

  return (
    <div>
      {tasks && <TasksList tasks={tasks} />}

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

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

const TasksList = ({ tasks }) => {
  if (!tasks?.length) return <div>No tasks</div>

  return (
    <div>
      {tasks.map((task, idx) => (
        <Task task={task} key={idx} />
      ))}
    </div>
  )
}

export default MainPage

TypeScript

src/client/MainPage.tsx

import getTasks from '@wasp/queries/getTasks'
import { useQuery } from '@wasp/queries'
import { Task } from '@wasp/entities'

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

  return (
    <div>
      {tasks && <TasksList tasks={tasks} />}

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

const Task = ({ task }: { task: Task }) => {
  return (
    <div>
      <input type="checkbox" id={String(task.id)} checked={task.isDone} />
      {task.description}
    </div>
  )
}

const TasksList = ({ tasks }: { tasks: Task[] }) => {
  if (!tasks?.length) return <div>No tasks</div>

  return (
    <div>
      {tasks.map((task, idx) => (
        <Task task={task} key={idx} />
      ))}
    </div>
  )
}

export default MainPage

Most of this code is regular React, the only exception being the special @wasp imports:

We could have called the query directly using getTasks(), but the useQuery hook makes it reactive: React will re-render the component every time the query changes. Remember that Wasp automatically refreshes queries whenever the data is modified.

With these changes, you should be seeing the text "No tasks" on the screen:

We'll create a form to add tasks in the next step 🪄