Скачать или смотреть How to Retrieve a Single Document from Firestore in Angular

Struggling with fetching a single document from Firestore in your Angular app? Discover a step-by-step solution that ensures you retrieve and log your data seamlessly, with promises and async handling!
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This video is based on the question https://stackoverflow.com/q/62629112/ asked by the user 'Nicolas HL' ( https://stackoverflow.com/u/13697423/ ) and on the answer https://stackoverflow.com/a/62638734/ provided by the user 'Ralemos' ( https://stackoverflow.com/u/12857703/ ) at 'Stack Overflow' website. Thanks to these great users and Stackexchange community for their contributions.

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Struggling to Retrieve a Single Document from Firestore in Angular?

If you're working on an Angular project integrated with Firebase and you find yourself unable to retrieve a specific document from Firestore, you're not alone. Many developers encounter this issue when they attempt to access data asynchronously. In this guide, we'll uncover why this happens and provide a clear, structured solution to help you overcome the problem.

The Problem Explained

When you attempt to get a document from Firestore, the operation is asynchronous. This means that when you call the function to retrieve the document, it doesn't pause the execution of your code while waiting for Firestore to respond. As a result, the console may log undefined before the actual data is returned.

Consider the following code snippet:

[[See Video to Reveal this Text or Code Snippet]]

In this code, the call to getOne('data_1') is executed, but it hasn't yet completed fetching the data when the console log runs. Thus, it outputs undefined.

Implementing the Solution

To ensure that your application correctly handles asynchronous data retrieval, you'll need to utilize promises effectively. Here’s how to transform your getOne method and update your component accordingly.

Step 1: Modify getOne Method

You'll want to return the promise from the getOne function to ensure that the calling function can handle the response once it's available.

Update your getOne method like this:

[[See Video to Reveal this Text or Code Snippet]]

Step 2: Handle the Promise in the Component

Next, you need to update your component’s constructor to handle the promise returned by getOne. The revised code will look like this:

[[See Video to Reveal this Text or Code Snippet]]

Why This Works

Asynchronous Handling: By returning a promise from the getOne method and handling it using then() in the constructor, you're ensuring that the console log only runs after the data has been retrieved.

Error Management: The catch block helps you manage any errors that occur during the fetch, allowing you to maintain robustness in your application.

Conclusion

Retrieving data from Firestore in an Angular application can be tricky due to asynchronous behavior, but with promises and proper handling, you can ensure that your data is fetched and displayed correctly. By following the structured approach outlined above, you can avoid the undefined issue and successfully retrieve single documents from your Firestore database.

Feel free to modify and adapt these solutions as per your application's needs!