369 lines
17 KiB
Markdown
369 lines
17 KiB
Markdown
# Managing Data
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At the end of [Routing](start/routing "Getting Started: Routing"), the online store application has a product catalog with two views: a product list and product details.
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Users can click on a product name from the list to see details in a new view, with a distinct URL, or route.
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This page guides you through creating the shopping cart in three phases:
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* Update the product details page to include a "Buy" button, which adds the current product to a list of products that a cart service manages.
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* Add a cart component, which displays the items in the cart.
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* Add a shipping component, which retrieves shipping prices for the items in the cart by using Angular's `HttpClient` to retrieve shipping data from a `.json` file.
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{@a services}
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## Services
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Services are an integral part of Angular applications. In Angular, a service is an instance of a class that you can make available to any part of your application using Angular's [dependency injection system](guide/glossary#dependency-injection-di "dependency injection definition").
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Services are the place where you share data between parts of your application. For the online store, the cart service is where you store your cart data and methods.
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{@a create-cart-service}
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## Create the shopping cart service
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Up to this point, users can view product information, and
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simulate sharing and being notified about product changes.
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They cannot, however, buy products.
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In this section, you add a "Buy" button to the product
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details page and set up a cart service to store information
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about products in the cart.
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<div class="alert is-helpful">
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Later, the [Forms](start/forms "Getting Started: Forms") part of
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this tutorial guides you through accessing this cart service
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from the page where the user checks out.
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Later, the [Forms](start/forms "Getting Started: Forms") part of this tutorial guides you through accessing this cart service from the page where the user checks out.
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</div>
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{@a generate-cart-service}
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### Define a cart service
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1. Generate a cart service.
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1. Right click on the `app` folder, choose `Angular Generator`, and choose `Service`. Name the new service `cart`.
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<code-example header="src/app/cart.service.ts" path="getting-started/src/app/cart.service.1.ts"></code-example>
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1. StackBlitz might generate the `@Injectable()` decorator without the `{ providedIn: 'root' }` statement as above. Instead, the generator provides the cart service in `app.module.ts` by default. For the purposes
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of this tutorial, either way works. The `@Injectable()` `{ providedIn: 'root' }` syntax allows [tree shaking](/guide/dependency-injection-providers#tree-shakable-providers), which is beyond the scope of this guide.
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1. In the `CartService` class, define an `items` property to store the array of the current products in the cart.
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<code-example path="getting-started/src/app/cart.service.ts" header="src/app/cart.service.ts" region="props"></code-example>
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1. Define methods to add items to the cart, return cart items, and clear the cart items:
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<code-example path="getting-started/src/app/cart.service.ts" header="src/app/cart.service.ts" region="methods"></code-example>
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* The `addToCart()` method appends a product to an array of `items`.
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* The `getItems()` method collects the items users add to the cart and returns each item with its associated quantity.
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* The `clearCart()` method returns an empty array of items.
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{@a product-details-use-cart-service}
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### Use the cart service
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This section walks you through using the cart service to add a product to the cart with a "Buy" button.
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1. Open `product-details.component.ts`.
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1. Configure the component to use the cart service.
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1. Import the cart service.
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<code-example header="src/app/product-details/product-details.component.ts" path="getting-started/src/app/product-details/product-details.component.ts" region="cart-service">
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</code-example>
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1. Inject the cart service by adding it to the `constructor()`.
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<code-example path="getting-started/src/app/product-details/product-details.component.ts" header="src/app/product-details/product-details.component.ts" region="inject-cart-service">
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</code-example>
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<!--
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To do: Consider defining "inject" and describing the concept of "dependency injection"
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-->
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1. Define the `addToCart()` method, which adds the current product to the cart.
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The `addToCart()` method does the following three things:
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* Receives the current `product`.
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* Uses the cart service's `addToCart()` method to add the product the cart.
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* Displays a message that you've added a product to the cart.
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<code-example path="getting-started/src/app/product-details/product-details.component.ts" header="src/app/product-details/product-details.component.ts" region="add-to-cart"></code-example>
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1. Update the product details template with a "Buy" button that adds the current product to the cart.
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1. Open `product-details.component.html`.
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1. Add a button with the label "Buy", and bind the `click()` event to the `addToCart()` method:
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<code-example header="src/app/product-details/product-details.component.html" path="getting-started/src/app/product-details/product-details.component.html">
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</code-example>
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1. To see the new "Buy" button, refresh the application and click on a product's name to display its details.
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<div class="lightbox">
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<img src='generated/images/guide/start/product-details-buy.png' alt="Display details for selected product with a Buy button">
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</div>
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1. Click the "Buy" button to add the product to the stored list of items in the cart and display a confirmation message.
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<div class="lightbox">
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<img src='generated/images/guide/start/buy-alert.png' alt="Display details for selected product with a Buy button">
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</div>
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## Create the cart page
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At this point, users can put items in the cart by clicking "Buy", but they can't yet see their cart.
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Create the cart page in two steps:
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1. Create a cart component and configure routing to the new component. At this point, the cart page will only have default text.
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1. Display the cart items.
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### Set up the component
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To create the cart page, begin by following the same steps you did to create the product details component and configure routing for the new component.
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1. Generate a cart component, named `cart`.
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Reminder: In the file list, right-click the `app` folder, choose `Angular Generator` and `Component`.
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<code-example header="src/app/cart/cart.component.ts" path="getting-started/src/app/cart/cart.component.1.ts"></code-example>
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1. Add routing (a URL pattern) for the cart component.
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Open `app.module.ts` and add a route for the component `CartComponent`, with a `path` of `cart`:
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<code-example header="src/app/app.module.ts" path="getting-started/src/app/app.module.ts" region="cart-route">
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</code-example>
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1. To see the new cart component, click the "Checkout" button. You can see the "cart works!" default text, and the URL has the pattern `https://getting-started.stackblitz.io/cart`, where `getting-started.stackblitz.io` may be different for your StackBlitz project.
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<div class="alert is-helpful">
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The starter code for the "Checkout" button already includes a `routerLink` for `/cart` the top-bar component.
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</div>
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<div class="lightbox">
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<img src='generated/images/guide/start/cart-works.png' alt="Display cart page before customizing">
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</div>
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### Display the cart items
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You can use services to share data across components:
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* The product details component already uses the cart service to add products to the cart.
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* This section shows you how to use the cart service to display the products in the cart.
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1. Open `cart.component.ts`.
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1. Configure the component to use the cart service.
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1. Import the `CartService` from the `cart.service.ts` file.
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<code-example header="src/app/cart/cart.component.ts" path="getting-started/src/app/cart/cart.component.2.ts" region="imports">
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</code-example>
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1. Inject the `CartService` so that the cart component can use it.
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<code-example path="getting-started/src/app/cart/cart.component.2.ts" header="src/app/cart/cart.component.ts" region="inject-cart">
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</code-example>
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1. Define the `items` property to store the products in the cart.
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<code-example path="getting-started/src/app/cart/cart.component.2.ts" header="src/app/cart/cart.component.ts" region="items">
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</code-example>
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1. Set the items using the cart service's `getItems()` method. Recall that you defined this method [when you generated `cart.service.ts`](#generate-cart-service).
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The resulting `CartComponent` class is as follows:
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<code-example path="getting-started/src/app/cart/cart.component.3.ts" header="src/app/cart/cart.component.ts" region="props-services">
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</code-example>
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1. Update the template with a header, and use a `<div>` with an `*ngFor` to display each of the cart items with its name and price.
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The resulting `CartComponent` template is as follows:
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<code-example header="src/app/cart/cart.component.html" path="getting-started/src/app/cart/cart.component.2.html" region="prices">
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</code-example>
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1. Test your cart component.
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1. Click on "My Store" to go to the product list page.
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1. Click on a product name to display its details.
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1. Click "Buy" to add the product to the cart.
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1. Click "Checkout" to see the cart.
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1. To add another product, click "My Store" to return to the product list.
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Repeat to add more items to the cart.
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<div class="lightbox">
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<img src='generated/images/guide/start/cart-page-full.png' alt="Cart page with products added">
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</div>
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<div class="alert is-helpful">
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StackBlitz tip: Any time the preview refreshes, the cart is cleared. If you make changes to the app, the page refreshes, so you'll need to buy products again to populate the cart.
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</div>
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<div class="alert is-helpful">
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For more information about services, see [Introduction to Services and Dependency Injection](guide/architecture-services "Architecture > Intro to Services and DI").
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</div>
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## Retrieve shipping prices
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<!-- Accessing data with the HTTP client -->
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Servers often return data in the form of a stream.
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Streams are useful because they make it easy to transform the returned data and make modifications to the way you request that data.
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The Angular HTTP client, `HttpClient`, is a built-in way to fetch data from external APIs and provide them to your app as a stream.
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This section shows you how to use the HTTP client to retrieve shipping prices from an external file.
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### Predefined shipping data
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The app StackBlitz generates for this guide comes with predefined shipping data in `assets/shipping.json`.
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Use this data to add shipping prices for items in the cart.
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<code-example header="src/assets/shipping.json" path="getting-started/src/assets/shipping.json">
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</code-example>
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### Use `HttpClient` in the `AppModule`
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Before you can use Angular's HTTP client, you must configure your app to use `HttpClientModule`.
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Angular's `HttpClientModule` registers the providers your app needs to use a single instance of the `HttpClient` service throughout your app.
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1. Open `app.module.ts`.
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This file contains imports and functionality that is available to the entire app.
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1. Import `HttpClientModule` from the `@angular/common/http` package at the top of the file with the other imports. As there are a number of other imports, this code snippet omits them for brevity. Be sure to leave the existing imports in place.
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<code-example header="src/app/app.module.ts" path="getting-started/src/app/app.module.ts" region="http-client-module-import">
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</code-example>
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1. Add `HttpClientModule` to the `AppModule` `@NgModule()` `imports` array to register Angular's `HttpClient` providers globally.
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<code-example path="getting-started/src/app/app.module.ts" header="src/app/app.module.ts" region="http-client-module">
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</code-example>
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### Use `HttpClient` in the cart service
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Now that the `AppModule` imports the `HttpClientModule`, the next step is to inject the `HttpClient` service into your service so your app can fetch data and interact with external APIs and resources.
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1. Open `cart.service.ts`.
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1. Import `HttpClient` from the `@angular/common/http` package.
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<code-example header="src/app/cart.service.ts" path="getting-started/src/app/cart.service.ts" region="import-http">
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</code-example>
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1. Inject `HttpClient` into the `CartService` constructor:
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<code-example path="getting-started/src/app/cart.service.ts" header="src/app/cart.service.ts" region="inject-http">
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</code-example>
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### Define the `get()` method
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Multiple components can leverage the same service.
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Later in this tutorial, the shipping component uses the cart service to retrieve shipping data via HTTP from the `shipping.json` file.
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First, define a `get()` method.
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1. Continue working in `cart.service.ts`.
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1. Below the `clearCart()` method, define a new `getShippingPrices()` method that uses the `HttpClient` `get()` method to retrieve the shipping data.
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<code-example header="src/app/cart.service.ts" path="getting-started/src/app/cart.service.ts" region="get-shipping"></code-example>
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<div class="alert is-helpful">
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For more information about Angular's `HttpClient`, see [HttpClient](guide/http "HttpClient guide").
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</div>
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## Define the shipping page
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Now that your app can retrieve shipping data, create a shipping component and template.
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1. Generate a new component named `shipping`.
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Reminder: In the file list, right-click the `app` folder, choose `Angular Generator` and `Component`.
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<code-example header="src/app/shipping/shipping.component.ts" path="getting-started/src/app/shipping/shipping.component.1.ts"></code-example>
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1. In `app.module.ts`, add a route for shipping. Specify a `path` of `shipping` and a component of `ShippingComponent`.
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<code-example header="src/app/app.module.ts" path="getting-started/src/app/app.module.ts" region="shipping-route"></code-example>
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There's no link to the new shipping component yet, but you can see its template in the preview pane by entering the URL its route specifies. The URL has the pattern: `https://getting-started.stackblitz.io/shipping` where the `getting-started.stackblitz.io` part may be different for your StackBlitz project.
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1. Modify the shipping component so it uses the cart service to retrieve shipping data via HTTP from the `shipping.json` file.
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1. Import the cart service.
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<code-example header="src/app/shipping/shipping.component.ts" path="getting-started/src/app/shipping/shipping.component.ts" region="imports"></code-example>
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1. Define a `shippingCosts` property.
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<code-example path="getting-started/src/app/shipping/shipping.component.ts" header="src/app/shipping/shipping.component.ts" region="props"></code-example>
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1. Inject the cart service in the `ShippingComponent` constructor:
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<code-example path="getting-started/src/app/shipping/shipping.component.ts" header="src/app/shipping/shipping.component.ts" region="inject-cart-service"></code-example>
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1. Set the `shippingCosts` property using the `getShippingPrices()` method from the cart service.
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<code-example path="getting-started/src/app/shipping/shipping.component.ts" header="src/app/shipping/shipping.component.ts" region="ctor"></code-example>
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1. Update the shipping component's template to display the shipping types and prices using the `async` pipe:
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<code-example header="src/app/shipping/shipping.component.html" path="getting-started/src/app/shipping/shipping.component.html"></code-example>
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The `async` pipe returns the latest value from a stream of data and continues to do so for the life of a given component. When Angular destroys that component, the `async` pipe automatically stops. For detailed information about the `async` pipe, see the [AsyncPipe API documentation](/api/common/AsyncPipe).
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1. Add a link from the cart page to the shipping page:
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<code-example header="src/app/cart/cart.component.html" path="getting-started/src/app/cart/cart.component.2.html"></code-example>
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1. Test your shipping prices feature:
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Click the "Checkout" button to see the updated cart. Remember that changing the app causes the preview to refresh, which empties the cart.
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<div class="lightbox">
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<img src='generated/images/guide/start/cart-empty-with-shipping-prices.png' alt="Cart with link to shipping prices">
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</div>
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Click on the link to navigate to the shipping prices.
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<div class="lightbox">
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<img src='generated/images/guide/start/shipping-prices.png' alt="Display shipping prices">
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</div>
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## Next steps
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Congratulations! You have an online store application with a product catalog and shopping cart. You can also look up and display shipping prices.
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To continue exploring Angular, choose either of the following options:
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* [Continue to the "Forms" section](start/forms "Getting Started: Forms") to finish the app by adding the shopping cart page and a checkout form.
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* [Skip ahead to the "Deployment" section](start/deployment "Getting Started: Deployment") to move to local development, or deploy your app to Firebase or your own server.
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