# 7. Queries and Data Sync

### Queries

In the previous section, we created `open_punches` as the variable which will contain all of our open punches. In order to populate that variable with data, we need to use a **Query**, which pulls data from the database in your app. Queries are defined in the **JavaScript** file of the relevant view. Before we define our query, a word about the `init()` and `resume()` functions in JavaScript:

### The `init()` and `resume()` Functions

You'll notice that every View in JourneyApps has an `init()` function in its **JavaScript** file. This function is automatically called every time that the user opens the particular view (every time the view loads), and therefore its purpose is to allow you to initialize any data that you might require in the view. For example, setting default values for new objects that are created, or performing Queries are typical things that you might do in the `init()` function.

You'll also notice that every View in JourneyApps has a `resume()` function in its **JavaScript** file. This function is automatically called every time that the user goes back to the particular view using a *dismiss* or *discard* navigation action (more about that later). It is typically used for advanced business logic and workflow. It can also be used to ensure that users don't access stale data when they navigate back to a specific view by refreshing any data that is used in that view.

### A Simple Query

In the Main View of your Punch List app, in your `main.js` file, you can create a query that pulls all punch list items from the database and stores them in the view variable `open_punches` as follows:

{% code title="main.js" %}

```javascript
// This function is called when the app navigates to this view (using a link)
function init() {
    // initialize any data here that should be available when the view is shown
    view.open_punches = DB.item.all();
}
```

{% endcode %}

* You can access your view variables and parameters in the JavaScript using the `view.` prefix. This allows you to differentiate between view variables and JS variables with the same name.
* `DB.item` is automatically made available because we've defined the `item` Object Type in our Data Model.

### Filtering

The query we've now added will show all punch list items in our `<object-list>` — however, we only want to show punches that have "Open" as their *status* (as defined in our Data Model). This can be done by **filtering** the query. To retrieve only the "Open" punches, change your code to the following:

{% code title="main.js" %}

```javascript
// This function is called each time the view is loaded

function init() {
    // initialize any data here that should be available when the view is shown
    view.open_punches = DB.item.where('status = ?', 'Open');
}
```

{% endcode %}

The first argument of the `where()` function is a string specifying the condition of how we want to match objects, and the arguments thereafter are the values that we are actually matching against.

### Global Automatic Data Sync

Recall from the [Global Automatic Data Sync section of the *What is JourneyApps?*](https://docs.journeyapps.com/reference/readme#powersync-global-automatic-data-sync) page that devices running your app automatically synchronize data from the cloud database to their local storage memory for offline access. This offline locally stored data is what is queried when you run a Query. (Please note the data is securely stored in a local database that is managed by the JourneyApps Container and is only accessible through the app).

Now let's see that data sync in action. First, go to the **Data Browser** action next to the Workspace Tabs in OXIDE, and from the list of available *deployments* select `testing`.

![](https://2865107717-files.gitbook.io/~/files/v0/b/gitbook-x-prod.appspot.com/o/spaces%2F9TCHLR67eLHBOjPvHhud%2Fuploads%2Fgit-blob-0d1587797cbad3833482676f231fa5120585e037%2Foxide-pl-data-browser.png?alt=media)

This will open the select *backend deployment* a new tab/window. After the redirect, click on **Item** in the lefthand sidebar and you should see the following:

![](https://2865107717-files.gitbook.io/~/files/v0/b/gitbook-x-prod.appspot.com/o/spaces%2F9TCHLR67eLHBOjPvHhud%2Fuploads%2Fgit-blob-a06403bf41f159ee0161a61fbd2d77f1a523a0ab%2Fbackend-items.png?alt=media)

The **"Testing" App Backend** is where you manage the data for your "Testing" environment (which is the environment that is used while you're developing apps in OXIDE — recall the [Components of JourneyApps](https://docs.journeyapps.com/reference/readme#journeyapps-building-blocks) and [Environments and Staged Deployment](https://docs.journeyapps.com/reference/readme#environments-and-staged-deployment) sections of the *What is JourneyApps?* page.)

### Create Some Data

So if you add some punch list items here, they will be synchronized to your mobile device. Add a couple of items by hitting **Create New Item**:

![](https://2865107717-files.gitbook.io/~/files/v0/b/gitbook-x-prod.appspot.com/o/spaces%2F9TCHLR67eLHBOjPvHhud%2Fuploads%2Fgit-blob-d8e4601d220cadfaa1f06507ae6ce3888ff346af%2Fbackend-items-new.png?alt=media)

![](https://2865107717-files.gitbook.io/~/files/v0/b/gitbook-x-prod.appspot.com/o/spaces%2F9TCHLR67eLHBOjPvHhud%2Fuploads%2Fgit-blob-1321506326a1d424d1926dd2e27cf210235ac7ce%2Fbackend-items-new-details.png?alt=media)

After creating some items like this, your list of Items should look like this:

![](https://2865107717-files.gitbook.io/~/files/v0/b/gitbook-x-prod.appspot.com/o/spaces%2F9TCHLR67eLHBOjPvHhud%2Fuploads%2Fgit-blob-796f9971d3e2b18e3866f261a57b278a02313c86%2Fbackend-items-list.png?alt=media)

### See Synchronized Data on Device

Now, refresh your app but remember that the `init()` function, which contains your query, only runs when you open a view (when the view loads), so to run the query again, you need to re-open your Main View.

* Close the app, don't just minimize it, and open it again. (Don't use the instructions to *Leave App*, you simply need to close the app and open it again)

You should now see the punch list items that you've entered on the web portal, that were automatically synchronized to your device:

{% tabs %}
{% tab title="Desktop" %}
![](https://2865107717-files.gitbook.io/~/files/v0/b/gitbook-x-prod.appspot.com/o/spaces%2F9TCHLR67eLHBOjPvHhud%2Fuploads%2Fgit-blob-9d281f88bcf81578e2188b05687af73f87362e66%2Fdesktop-pl-main-items.png?alt=media)
{% endtab %}

{% tab title="Mobile" %}
![](https://2865107717-files.gitbook.io/~/files/v0/b/gitbook-x-prod.appspot.com/o/spaces%2F9TCHLR67eLHBOjPvHhud%2Fuploads%2Fgit-blob-a93945e0fa61cfb962d29969429f98df7f3608cf%2Fmobile-pl-main-items.png?alt=media)
{% endtab %}
{% endtabs %}

In summary, you've seen how JourneyApps' built-in automatic data synchronization works, and how you can use a Query to pull data from the on device database and display it in your Views. Now let's continue to work on fleshing out the functionality of our Punch List app in the next sections.