What is the best way to retrieve a value from $http or $resource using this filter?

Question

What is the best way to retrieve a value from $http or $resource using this filter?

Within my HTML, I have a structure that looks like {{ i.userId | userName }}. Essentially, I am attempting to convert this into a name by utilizing a filter. However, I am encountering numerous challenges with the asynchronous function required to retrieve the data.

app.filter('userName', function($http) {
    return function(value) {
        if (!value) return '';
        
        var user;
        $http({
            method: 'GET',
            url: 'http://localhost:3000/api/Users?filter={"where":{"id":' + value + '}}'
        }).success(function(response) {
                user = response;
        });
        
        return user.name;
    }
});

I attempted to organize it in a callback format, but unfortunately, I was unable to make it function correctly.

javascript angularjs

Answer 1

Answer №1

It is important to note that using async calls in filters may not work as expected in Angular. Filters are typically assumed to be side effect free and are only executed when the model changes. Therefore, if an async call is made within a filter, it may not return in time before the filter has completed its operation. This means that the filter will not be called again until the model updates.

To address this issue, you can make the filter stateful by setting the $stateful property on the filter function:

function filterFunction(value) {
    if (!value) return '';

    var user;
    $http({
        method: 'GET',
        url: 'http://localhost:3000/api/Users?filter=                                                                                                      
                                 {"where":{"id":' + value + '}}'
    }).success(function (response) {
        user = response;
    });

    return user.name;

}
filterFunction.$stateful = true;
return filterFunction;

However, making the filter stateful in this way can impact performance, as it will be evaluated on each digest cycle by Angular.

For a more efficient solution, consider fetching the user list in advance and implementing a custom filter that searches through this preloaded list.

For more information on filters, please refer to the Angular developer guide.

Answer 2

It is important to note that using async calls in filters may not work as expected in Angular. Filters are typically assumed to be side effect free and are only executed when the model changes. Therefore, if an async call is made within a filter, it may not return in time before the filter has completed its operation. This means that the filter will not be called again until the model updates.

To address this issue, you can make the filter stateful by setting the $stateful property on the filter function:

function filterFunction(value) {
    if (!value) return '';

    var user;
    $http({
        method: 'GET',
        url: 'http://localhost:3000/api/Users?filter=                                                                                                      
                                 {"where":{"id":' + value + '}}'
    }).success(function (response) {
        user = response;
    });

    return user.name;

}
filterFunction.$stateful = true;
return filterFunction;

However, making the filter stateful in this way can impact performance, as it will be evaluated on each digest cycle by Angular.

For a more efficient solution, consider fetching the user list in advance and implementing a custom filter that searches through this preloaded list.

For more information on filters, please refer to the Angular developer guide.

What is the best way to retrieve a value from $http or $resource using this filter?

Answer №1

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