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Overview

Once you have defined a metric, you are ready to attach it to a resource. Each resource generated by Nova contains a cards method. To attach a metric to a resource, you should simply add it to the array of metrics / cards returned by this method: 
use App\Nova\Metrics\UsersPerDay;
use Laravel\Nova\Http\Requests\NovaRequest;

/**
 * Get the cards available for the resource.
 *
 * @param  \Laravel\Nova\Http\Requests\NovaRequest  $request
 * @return array
 */
public function cards(NovaRequest $request)
{
    return [
        new UsersPerDay
    ];
}
Alternatively, you may use the make method to instantiate your metric: 
use App\Nova\Metrics\UsersPerDay;
use Laravel\Nova\Http\Requests\NovaRequest;

/**
 * Get the cards available for the resource.
 *
 * @param  \Laravel\Nova\Http\Requests\NovaRequest  $request
 * @return array
 */
public function cards(NovaRequest $request)
{
    return [
        UsersPerDay::make()
    ];
}
Any arguments passed to the make method will be passed to the constructor of your metric.

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Detail Metrics

In addition to placing metrics on the resource index page, you may also attach a metric to the resource detail page. For example, if you are building a podcasting application, you may wish to display the total number of podcasts created by a specific user over time. To instruct a metric to be displayed on the detail page instead of the index page, invoke the onlyOnDetail method when registering your metric: 
/**
 * Get the cards available for the request.
 *
 * @param  \Laravel\Nova\Http\Requests\NovaRequest  $request
 * @return array
 */
public function cards(NovaRequest $request)
{
    return [
        (new Metrics\PodcastCount)->onlyOnDetail(),
    ];
}
Of course, you will need to modify your metric’s query to only gather metric data on the resource for which it is currently being displayed. To accomplish this, your metric’s calculate method may access the resourceId property on the incoming $request: 
use App\Models\Podcast;

return $this->count($request, Podcast::where('user_id', $request->resourceId));

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Dashboard Metrics

You are also free to add metrics to your primary Nova “dashboard”, which is the default page that Nova displays after login. By default, this page displays some helpful links to the Nova documentation via the built-in Help card. To add a metric to your dashboard, add the metric to the array of cards returned by the cards method of your app/Nova/Dashboards/Main class: 
use App\Nova\Metrics\NewUsers;

/**
 * Get the cards that should be displayed on the Nova dashboard.
 *
 * @return array
 */
protected function cards()
{
    return [
        new NewUsers,
    ];
}

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Authorization

If you would like to only expose a given metric to certain users, you may invoke the canSee method when registering your metric. The canSee method accepts a closure which should return true or false. The closure will receive the incoming HTTP request: 
use App\Models\User;
use Laravel\Nova\Http\Requests\NovaRequest;

/**
 * Get the cards available for the resource.
 *
 * @param  \Laravel\Nova\Http\Requests\NovaRequest  $request
 * @return array
 */
public function cards(NovaRequest $request)
{
    return [
        (new Metrics\UsersPerDay)->canSee(function ($request) {
            return $request->user()->can('viewUsersPerDay', User::class);
        }),
    ];
}
In the example above, we are using Laravel’s Authorizable trait’s can method on our User model to determine if the authorized user is authorized for the viewUsersPerDay action. However, since proxying to authorization policy methods is a common use-case for canSee, you may use the canSeeWhen method to achieve the same behavior. The canSeeWhen method has the same method signature as the Illuminate\Foundation\Auth\Access\Authorizable trait’s can method: 
return [
    (new Metrics\UsersPerDay)->canSeeWhen(
        'viewUsersPerDay', User::class
    ),
];

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Default Metric Range

You may wish to initially load a certain metric range by default. You can pass the range’s array key to the defaultRange method of the metric to accomplish this: 
use App\Nova\Metrics\NewUsers;

/**
 * Get the cards that should be displayed on the Nova dashboard.
 *
 * @return array
 */
protected function cards()
{
    return [
        NewUsers::make()->defaultRange('YTD'),
    ];
}

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Metric Sizes

By default, metrics take up one-third of the Nova content area. However, you are free to make them larger. To accomplish this, call the width method when registering the metric: 
/**
 * Get the cards available for the request.
 *
 * @param  \Laravel\Nova\Http\Requests\NovaRequest  $request
 * @return array
 */
public function cards(NovaRequest $request)
{
    return [
        // Two-thirds of the content area...
        (new Metrics\UsersPerDay)->width('2/3'),

        // Full width...
        (new Metrics\UsersPerDay)->width('full'),
    ];
}
When the metric width is set to full, the height of the card will become dynamic. You may explicitly define this behaviour by calling the fixedHeight or dynamicHeight methods: 
/**
 * Get the cards available for the request.
 *
 * @param  \Laravel\Nova\Http\Requests\NovaRequest  $request
 * @return array
 */
public function cards(NovaRequest $request)
{
    return [
        (new Metrics\UsersPerDay)->width('full')->fixedHeight(),
        (new Metrics\UsersPerDay)->width('full')->dynamicHeight(),
    ];
}

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Metric Help Text / Tooltips

Sometimes a metric needs to offer the user more context about how the value is calculated or other details related to the metric’s value. To provide this context, Nova allows you to define a help text “tooltip”, which can be registered similarly to Field Help Text:
Metric Help Tooltip
To enable the tooltip, invoke the help method while registering your metric. The help method receives the help text as its only argument: 
/**
 * Get the cards available for the request.
 *
 * @param  \Laravel\Nova\Http\Requests\NovaRequest  $request
 * @return array
 */
public function cards(NovaRequest $request)
{
    return [
        (new TotalUsers)
            ->help('This is calculated using all users that are active and not banned.'),
    ];
}
You may also use HTML when defining your help text. For example, you may pass a rendered Blade template to the help method: 
(new TotalUsers)
    ->help(view('nova.metrics.total-users.tooltip')->render()),

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Refreshing Metrics

Laravel Nova will automatically fetch updated results (without requiring the user to refresh the page) for metrics attached to a resource based on following events:
EventBehaviour
Resource DeletedAutomatic Update
Resource RestoredAutomatic Update
Action ExecutedOnly update if the metric’s refreshWhenActionsRun method is invoked during registration
Filter ChangeOnly update if the metric’s refreshWhenFiltersChange method is invoked during registration

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Refresh After Actions

By default, Nova does not automatically update metric results after an action is executed without the user manually refreshing the page; however, you may indicate that metrics should automatically refresh after actions have executed by invoking the refreshWhenActionsRun method when registering your metric: 
public function cards(NovaRequest $request)
{
    return [
        TotalUsers::make()->refreshWhenActionsRun(),
    ];
}

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Refresh After Filter Changes

Likewise, Laravel Nova will only automatically update a metric’s value when a page’s selected filters change if the metric’s refreshWhenFiltersChange method is invoked when the metric is registered: 
public function cards(NovaRequest $request)
{
    return [
        TotalUsers::make()->refreshWhenFiltersChange(),
    ];
}
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