Fixing InjectQueryParams Null Emission In Ngxtension

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Fixing injectQueryParams Null Emission in ngxtension

Hey guys! So, you're wrestling with injectQueryParams in your ngxtension setup, huh? Specifically, you're seeing it emit null when there are no query parameters present, and that's messing with your filtering logic. You want undefined instead, so you can differentiate between a deliberately set null value and a filter that's simply not active. Let's dive into this and see how we can sort it out. Trust me, you're not alone in this, and we'll get through it together!

Understanding the Problem

First off, let's make sure we're all on the same page. The injectQueryParams function in ngxtension is designed to inject query parameters from the URL into your Angular components or services as an Observable. This is super handy for creating reactive UIs that respond to changes in the URL. However, by default, when no query parameters are present, or a specific parameter is missing, injectQueryParams emits null. This behavior can be a bit of a pain when you're trying to use these parameters for filtering, where null and undefined have distinct meanings.

The core issue here is the semantic difference between null and undefined. In JavaScript (and therefore TypeScript), null explicitly means "no value," while undefined means a variable has been declared but has not yet been assigned a value. In the context of filtering, null might mean "show items where this property is explicitly null," whereas undefined might mean "don't filter on this property at all." This distinction is crucial for creating flexible and intuitive filtering mechanisms.

Now, you've already tried a few things, like using defaultValue and manually parsing the values to override null with undefined. The fact that these approaches didn't work suggests that the injectQueryParams function might be a bit too opinionated about how it handles missing parameters. But don't worry, we have a few more tricks up our sleeves!

Potential Solutions and Workarounds

Okay, let's explore some strategies to get injectQueryParams to play nice with your filtering logic. Here are a few options you can try:

1. Using pipe and map to Transform the Emitted Value

One of the most flexible ways to handle this is by using the pipe and map operators from RxJS. These operators allow you to transform the emitted values from the Observable returned by injectQueryParams before they reach your component or service. Here's how you can do it:

import { injectQueryParams } from '@ngxtension/platform';
import { map } from 'rxjs/operators';
import { of } from 'rxjs';

const myParam$ = injectQueryParams('myParam').pipe(
  map(value => value === null ? undefined : value)
);

In this example, we're using the map operator to check if the emitted value is null. If it is, we replace it with undefined. Otherwise, we leave the value as is. This ensures that your component or service only receives either a valid value or undefined.

Why this works: The pipe and map operators allow you to intercept and transform the data stream from injectQueryParams without modifying the original function's behavior. This is a non-invasive way to achieve the desired result.

2. Creating a Custom injectQueryParams Wrapper

If you find yourself doing this transformation in multiple places, it might be worth creating a custom wrapper around injectQueryParams. This wrapper can encapsulate the transformation logic and provide a cleaner API for your components and services. Here's how you can create such a wrapper:

import { injectQueryParams } from '@ngxtension/platform';
import { map } from 'rxjs/operators';
import { Observable } from 'rxjs';

function injectQueryParamsOrDefault<T>(paramName: string): Observable<T | undefined> {
  return injectQueryParams<T>(paramName).pipe(
    map(value => value === null ? undefined : value)
  );
}

// Usage
const myParam$ = injectQueryParamsOrDefault<string>('myParam');

In this example, we've created a function called injectQueryParamsOrDefault that takes a parameter name as input and returns an Observable. Inside this function, we call the original injectQueryParams function and then use the pipe and map operators to transform the emitted value. This wrapper function provides a more convenient way to get the desired behavior without having to repeat the transformation logic in multiple places.

Why this works: This approach promotes code reuse and reduces the risk of errors. It also makes your code more readable and maintainable.

3. Using BehaviorSubject for More Control

For even more control, you can use a BehaviorSubject to manage the query parameter. This allows you to set an initial value and explicitly control when and how the value is updated. Here's how you can do it:

import { injectQueryParams } from '@ngxtension/platform';
import { BehaviorSubject } from 'rxjs';
import { distinctUntilChanged } from 'rxjs/operators';

const myParamSubject = new BehaviorSubject<string | undefined>(undefined);

injectQueryParams<string>('myParam').pipe(
  distinctUntilChanged(),
).subscribe(value => {
  myParamSubject.next(value === null ? undefined : value);
});

const myParam$ = myParamSubject.asObservable();

In this example, we're creating a BehaviorSubject with an initial value of undefined. We then subscribe to the Observable returned by injectQueryParams and update the BehaviorSubject whenever the query parameter changes. The distinctUntilChanged operator ensures that we only update the BehaviorSubject when the value actually changes, preventing unnecessary emissions.

Why this works: This approach gives you complete control over the value of the query parameter. You can set an initial value, update the value based on the query parameters, and even manually set the value if needed.

4. Contributing to ngxtension

Now, let's talk about the bigger picture. You mentioned the possibility of submitting a pull request (PR) to ngxtension to address this issue directly. That's a fantastic idea! If you believe that the current behavior of injectQueryParams is not ideal and that it should be possible to override the null emission, then you should definitely consider contributing to the library. Your perspective as a user is valuable, and your contribution could benefit many other developers.

How to contribute:

  1. Fork the ngxtension repository: Go to the ngxtension GitHub repository and click the "Fork" button to create your own copy of the repository.
  2. Create a branch: In your forked repository, create a new branch for your changes. This helps keep your changes separate from the main codebase.
  3. Implement the changes: Modify the injectQueryParams function to allow users to specify a default value or a transformation function that is applied when the query parameter is missing or null.
  4. Write tests: Add unit tests to ensure that your changes work as expected and that they don't break any existing functionality.
  5. Submit a pull request: Once you're satisfied with your changes, submit a pull request to the main ngxtension repository. Be sure to include a detailed description of your changes and why you believe they are necessary.

Is Your Filtering Approach Wrong?

Now, let's take a step back and consider whether your filtering approach might be contributing to the problem. You mentioned that you're using null to explicitly indicate that a value should be null. While this is a valid approach, it's worth considering whether it's the most intuitive or flexible approach.

Alternative filtering approaches:

  • Using undefined for unset filters: As you've already suggested, using undefined to indicate that a filter is not set can be a more intuitive approach. This allows you to differentiate between a filter that is explicitly set to null and a filter that is simply not active.
  • Using a separate flag to indicate whether a filter is active: Another approach is to use a separate boolean flag to indicate whether a filter is active. This can be useful when you need to explicitly control whether a filter is applied, regardless of its value.
  • Using a more complex data structure to represent filters: For more complex filtering scenarios, you might consider using a more complex data structure to represent your filters. This could include information about the filter type, the filter value, and whether the filter is active.

Conclusion

Alright, guys, we've covered a lot of ground here. You're definitely not alone in facing this issue with injectQueryParams. It's a common challenge when working with reactive query parameters and filtering. Remember, the key is to transform the emitted values to match your filtering logic. Whether you choose to use pipe and map, create a custom wrapper, or use a BehaviorSubject, the goal is the same: to ensure that your components and services receive the values they expect. And don't forget, contributing to ngxtension is a great way to make a lasting impact on the library and the community. Keep up the great work, and happy coding!