How can I retrieve information from a Behavior Subject within an Angular service?

Question

How can I retrieve information from a Behavior Subject within an Angular service?

My goal in using BehaviouSubject was to streamline API calls and share the data with multiple components within the same route. While I've successfully achieved this, I'm facing challenges when trying to filter the received data.

Here is a stackblitz example that I have put together:

https://stackblitz.com/edit/angular-xtne5y

One of my components displays a table, while the other component needs to extract specific information based on individual object key values (e.g., counting complete/incomplete todos). Due to the necessity of using the async pipe throughout the template, performing operations like filtering becomes impractical. Is there a more efficient way to tackle this issue?

It's crucial for me to maintain reusability of the extracted data.

javascript angular typescript rxjs

Answer 1

Answer №1

If you want to achieve the desired outcome, consider incorporating another custom pipe alongside the async pipe to extract specific properties from your data.

I have made modifications to your stackblitz example and implemented the solution. You can view the updated code in action here.

The key is to apply a custom pipe, as demonstrated below:

{{ todos$ | async | myCustomFilter }}

In the provided example (on stackblitz), I have utilized the following:

    <p>
      Number of Completed Todos: {{ (todos$ | async | filterByCondition: {property: 'completed', value: true}).length }}
    </p>

    <p>
      Number of Incomplete Todos: {{ (todos$ | async | filterByCondition: {property: 'completed', value: false}).length }}
    </p>

Update based on feedback

You have two options to achieve your objective: 1) Implement a custom pipe, where you can customize the conditions similar to what has been demonstrated, or create your own logic for evaluation by passing parameters to the pipe (as shown in the example with the args property).

For instance:

    <div>{{$todos | async | filterTodo: 'byDate'}}</div>

You can then handle the logic within your pipe filterTodo based on the 'byDate' value.

2) Utilize different observables for distinct data sets.

  class MyComponent {
    todos$;
    completedTodos$;
    constructor() {
        this.todos$ = this.someService.getTodos(); // from behavior subject
        this.completedTodos$ = this.todos$.pipe(
            filter((item) => {
                // Add your filtering logic here
            })
        )
    }

  }

Answer 2

If you want to achieve the desired outcome, consider incorporating another custom pipe alongside the async pipe to extract specific properties from your data.

I have made modifications to your stackblitz example and implemented the solution. You can view the updated code in action here.

The key is to apply a custom pipe, as demonstrated below:

{{ todos$ | async | myCustomFilter }}

In the provided example (on stackblitz), I have utilized the following:

    <p>
      Number of Completed Todos: {{ (todos$ | async | filterByCondition: {property: 'completed', value: true}).length }}
    </p>

    <p>
      Number of Incomplete Todos: {{ (todos$ | async | filterByCondition: {property: 'completed', value: false}).length }}
    </p>

Update based on feedback

You have two options to achieve your objective: 1) Implement a custom pipe, where you can customize the conditions similar to what has been demonstrated, or create your own logic for evaluation by passing parameters to the pipe (as shown in the example with the args property).

For instance:

    <div>{{$todos | async | filterTodo: 'byDate'}}</div>

You can then handle the logic within your pipe filterTodo based on the 'byDate' value.

2) Utilize different observables for distinct data sets.

  class MyComponent {
    todos$;
    completedTodos$;
    constructor() {
        this.todos$ = this.someService.getTodos(); // from behavior subject
        this.completedTodos$ = this.todos$.pipe(
            filter((item) => {
                // Add your filtering logic here
            })
        )
    }

  }

Answer 3

Answer №2

In my experience working on projects involving creating TODO lists, I have found that subscribing to the URL to fetch data and setting up a Redux Store is an effective approach. You can find more information about this approach in this article.

interface ProductTodos {
    product: {title:string,iscompleted:boolean,id:string/number},
    todos?: any[]
}

By dispatching actions like "PUSH" when fetching Todos, you can append each TODO as an object of type product to the todos array in the interface.

When instantiating the redux Store in the Component Class, loop through the "todos" array to check for id and isCompleted status.

This allows you to iterate through each object and populate your tables according to their completion status.

You can also view my ReduxDemo in Angular 4 by visiting this link.

Answer 4

In my experience working on projects involving creating TODO lists, I have found that subscribing to the URL to fetch data and setting up a Redux Store is an effective approach. You can find more information about this approach in this article.

interface ProductTodos {
    product: {title:string,iscompleted:boolean,id:string/number},
    todos?: any[]
}

By dispatching actions like "PUSH" when fetching Todos, you can append each TODO as an object of type product to the todos array in the interface.

When instantiating the redux Store in the Component Class, loop through the "todos" array to check for id and isCompleted status.

This allows you to iterate through each object and populate your tables according to their completion status.

You can also view my ReduxDemo in Angular 4 by visiting this link.

How can I retrieve information from a Behavior Subject within an Angular service?

Answer №1

Update based on feedback

Answer №2

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