meteor/v3-docs/docs/tutorials/react/2.collections.md

## 2: Collections

Meteor already sets up MongoDB for you. In order to use our database, we need to create a _collection_, which is where we will store our _documents_, in our case our `tasks`.

> You can read more about collections [here](https://v3-docs.meteor.com/api/collections.html).

In this step, we will implement all the necessary code to have a basic collection for our tasks up and running using React hooks.

### 2.1: Create Tasks Collection {#create-tasks-collection}

We can create a new collection to store our tasks by creating a new file at `imports/api/TasksCollection.js` which instantiates a new Mongo collection and exports it.

::: code-group

```js [imports/api/TasksCollection.js]
import { Mongo } from "meteor/mongo";

export const TasksCollection = new Mongo.Collection("tasks");
```

:::

Notice that we stored the file in the `imports/api` directory, which is a place to store API-related code, like publications and methods. You can name this folder as you want, this is just a choice.

You can delete the `links.js` file in this folder as we are not going to use this collection.

> You can read more about app structure and imports/exports [here](http://guide.meteor.com/structure.html).

### 2.2: Initialize Tasks Collection {#initialize-tasks-collection}

For our collection to work, you need to import it in the server so it sets some plumbing up.

You can either use `import "/imports/api/TasksCollection"` or `import { TasksCollection } from "/imports/api/TasksCollection"` if you are going to use on the same file, but make sure it is imported.

Now it is easy to check if there is data or not in our collection, otherwise, we can insert some sample data easily as well.

You don't need to keep the old content of `server/main.js`.

::: code-group

```js [server/main.js]
import { Meteor } from "meteor/meteor";
import { TasksCollection } from "/imports/api/TasksCollection";

const insertTask = (taskText) =>
  TasksCollection.insertAsync({ text: taskText });

Meteor.startup(async () => {
  if ((await TasksCollection.find().countAsync()) === 0) {
    [
      "First Task",
      "Second Task",
      "Third Task",
      "Fourth Task",
      "Fifth Task",
      "Sixth Task",
      "Seventh Task",
    ].forEach(insertTask);
  }
});
```

:::

So you are importing the `TasksCollection` and adding a few tasks to it iterating over an array of strings and for each string calling a function to insert this string as our `text` field in our `task` document.

### 2.3: Render Tasks Collection {#render-tasks-collection}

Now comes the fun part, you will render the tasks using a React Function Component and a Hook called `useTracker` from a package called [react-meteor-data](https://atmospherejs.com/meteor/react-meteor-data).

> Meteor works with Meteor packages and NPM packages, usually, Meteor packages are using Meteor internals or other Meteor packages.

This package is already included in the React skeleton (`meteor create yourproject`) so you don't need to add it but you can always add Meteor packages running `meteor add package-name`:

```shell
meteor add react-meteor-data
```

Now you are ready to import code from this package, when importing code from a Meteor package the only difference from NPM modules is that you need to prepend `meteor/` in the from part of your import.

The `useTracker` function exported by `react-meteor-data` is a React Hook that allows you to have reactivity in your React components. Every time the data changes through reactivity your component will re-render. Cool, right?

> For more information about React Hooks read [here](https://reactjs.org/docs/hooks-faq.html).

::: code-group

```javascript [imports/ui/App.jsx]
import React from "react";
import { useTracker } from "meteor/react-meteor-data";
import { TasksCollection } from "/imports/api/TasksCollection";
import { Task } from "./Task";

export const App = () => {
  const tasks = useTracker(() => TasksCollection.find({}).fetch());

  return (
    <div>
      <h1>Welcome to Meteor!</h1>

      <ul>
        {tasks.map((task) => (
          <Task key={task._id} task={task} />
        ))}
      </ul>
    </div>
  );
};
```

:::

But wait! Something is missing. If you run your app now, you'll see that you don't render any tasks.

That's because we need to publish our data to the client.

Fist, create a publication for our tasks:

`imports/api/TasksPublications.js`

```javascript
import { Meteor } from "meteor/meteor";
import { TasksCollection } from "./TasksCollection";

Meteor.publish("tasks", () => {
  return TasksCollection.find();
});
```

Now, we need to import this file in our server:

::: code-group

```js [server/main.js]
...
import { TasksCollection } from '/imports/api/TasksCollection';

import "../imports/api/TasksPublications"; // [!code highlight]

const insertTask = taskText => TasksCollection.insertAsync({ text: taskText });
...
```

:::

The only thing left is subscribe to this publication:

`imports/ui/App.jsx`

```javascript
import React from 'react';
import { useTracker, useSubscribe } from 'meteor/react-meteor-data'; // [!code highlight]
import { TasksCollection } from '/imports/api/TasksCollection';
import { Task } from './Task';

export const App = () => {

  const isLoading = useSubscribe("tasks");  // [!code highlight]
  const tasks = useTracker(() => TasksCollection.find({}).fetch());

  if (isLoading()) {
    return <div>Loading...</div>;
  }
  ...
}
```

As you can see, when subscribing to a publication using `useSubscribe` you'll get a `isLoading` function, that you can use to render some loading component before the data is ready.

> For more information on Publications/Subscriptions, please check our [docs](https://v3-docs.meteor.com/api/meteor.html#pubsub).

See how your app should look like now:

<img width="200px" src="/tutorials/react/assets/collections-tasks-list.png"/>

You can change your data on MongoDB in the server and your app will react and re-render for you.

You can connect to your MongoDB running `meteor mongo` in the terminal from your app folder or using a Mongo UI client, like [NoSQLBooster](https://nosqlbooster.com/downloads). Your embedded MongoDB is running in port `3001`.

See how to connect:

<img width="500px" src="/tutorials/react/assets/collections-connect-db.png"/>

See your database:

<img width="500px" src="/tutorials/react/assets/collections-see-database.png"/>

You can double-click your collection to see the documents stored on it:

<img width="500px" src="/tutorials/react/assets/collections-documents.png"/>

In the next step, we are going to create tasks using a form.