How to Extract Certain Fields from an HTTP Response Object in Angular

Описание: Learn how to efficiently `extract specific fields` from an HTTP response in Angular using the HttpClient service. This guide will guide you step-by-step with practical examples!
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This video is based on the question https://stackoverflow.com/q/69552524/ asked by the user 'Luka Reeson' ( https://stackoverflow.com/u/15743106/ ) and on the answer https://stackoverflow.com/a/69552601/ provided by the user 'DTul' ( https://stackoverflow.com/u/8731503/ ) at 'Stack Overflow' website. Thanks to these great users and Stackexchange community for their contributions.

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Extracting Certain Fields from an HTTP Response Object in Angular

When working with HTTP responses in Angular, especially from APIs that return a vast amount of data, you may find yourself needing only a small subset of this data. For instance, you might need specific fields from a weather API response but don't want to handle the entire object. If you’re new to Angular or TypeScript, don’t worry; in this guide, we’ll break down how to extract those crucial fields effectively.

Understanding the Problem

Let’s take a real-life example where you're fetching weather data for a city using the OpenWeatherMap API. You may have set up a service to make the GET request as follows:

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In your component, you might log the entire response to the console, like this:

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However, logging the response (data) shows a large object with many fields, but you’re only interested in a few of them. This is where we can apply some mapping to simplify your code and focus on the essential information.

Solution Overview

There are two main approaches to extract specific fields from the HTTP response object in Angular:

Mapping in the Service: Modify the service method to return a specific object.

Mapping in the Component: Extract the required fields directly in the component after the HTTP request.

Option 1: Mapping in the Service

Let’s update our getCity function in the CityService to return an object of type City, which only includes the fields you care about.

Step-by-Step Guide

Define the City Interface: First, ensure you have an interface that defines what fields you're interested in:

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Modify the Service: Now, restructure the getCity method to include the mapping logic using pipe and map:

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This method will now return a simplified object that contains only the fields you defined in the City interface.

Option 2: Mapping in the Component

If you prefer to keep your service method intact and want to handle the mapping in your component, here's how to do it:

Fetch Data as Usual:

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This way, you're doing the heavy lifting within your component, which provides flexibility depending on your needs.

Conclusion

Extracting specific fields from an HTTP response in Angular is straightforward with the use of the RxJS map operator. By employing this practice, you not only streamline your code but also enhance readability and maintainability. Depending on your project needs, you can choose to handle mapping within the service or component to achieve the desired result efficiently. Happy coding!